FFmpeg源代码简单分析:结构体成员管理系统-AVClass
=====================================================
FFmpeg的库函数源代码分析文章列表:
【架构图】
【通用】
FFmpeg 源代码简单分析:av_register_all()
FFmpeg 源代码简单分析:avcodec_register_all()
FFmpeg 源代码简单分析:内存的分配和释放(av_malloc()、av_free()等)
FFmpeg 源代码简单分析:常见结构体的初始化和销毁(AVFormatContext,AVFrame等)
FFmpeg 源代码简单分析:av_find_decoder()和av_find_encoder()
FFmpeg 源代码简单分析:avcodec_open2()
FFmpeg 源代码简单分析:avcodec_close()
【解码】
图解FFMPEG打开媒体的函数avformat_open_input
FFmpeg 源代码简单分析:avformat_open_input()
FFmpeg 源代码简单分析:avformat_find_stream_info()
FFmpeg 源代码简单分析:av_read_frame()
FFmpeg 源代码简单分析:avcodec_decode_video2()
FFmpeg 源代码简单分析:avformat_close_input()
【编码】
FFmpeg 源代码简单分析:avformat_alloc_output_context2()
FFmpeg 源代码简单分析:avformat_write_header()
FFmpeg 源代码简单分析:avcodec_encode_video()
FFmpeg 源代码简单分析:av_write_frame()
FFmpeg 源代码简单分析:av_write_trailer()
【其它】
FFmpeg源代码简单分析:日志输出系统(av_log()等)
FFmpeg源代码简单分析:结构体成员管理系统-AVClass
FFmpeg源代码简单分析:结构体成员管理系统-AVOption
FFmpeg源代码简单分析:libswscale的sws_getContext()
FFmpeg源代码简单分析:libswscale的sws_scale()
FFmpeg源代码简单分析:libavdevice的avdevice_register_all()
FFmpeg源代码简单分析:libavdevice的gdigrab
【脚本】
【H.264】
=====================================================
打算写两篇文章记录FFmpeg中和AVOption有关的源代码。AVOption用于在FFmpeg中描述结构体中的成员变量。它最主要的作用可以概括为两个字:“赋值”。一个AVOption结构体包含了变量名称,简短的帮助,取值等等信息。
所有和AVOption有关的数据都存储在AVClass结构体中。如果一个结构体(例如AVFormatContext或者AVCodecContext)想要支持AVOption的话,它的第一个成员变量必须是一个指向AVClass结构体的指针。该AVClass中的成员变量option必须指向一个AVOption类型的静态数组。
何为AVOption?
AVOption是用来设置FFmpeg中变量的值的结构体。可能说到这个作用有的人会奇怪:设置系统中变量的值,直接使用等于号“=”就可以,为什么还要专门定义一个结构体呢?其实AVOption的特点就在于它赋值时候的灵活性。AVOption可以使用字符串为任何类型的变量赋值。传统意义上,如果变量类型为int,则需要使用整数来赋值;如果变量为double,则需要使用小数来赋值;如果变量类型为char *,才需要使用字符串来赋值。而AVOption将这些赋值“归一化”了,统一使用字符串赋值。例如给int型变量qp设定值为20,通过AVOption需要传递进去一个内容为“20”的字符串。
此外,AVOption中变量的名称也使用字符串来表示。结合上面提到的使用字符串赋值的特性,我们可以发现使用AVOption之后,传递两个字符串(一个是变量的名称,一个是变量的值)就可以改变系统中变量的值。
上文提到的这种方法的意义在哪里?我个人感觉对于直接使用C语言进行开发的人来说,作用不是很明显:完全可以使用等于号“=”就可以进行各种变量的赋值。但是对于从外部系统中调用FFmpeg的人来说,作用就很大了:从外部系统中只可以传递字符串给内部系统。比如说对于直接调用ffmpeg.exe的人来说,他们是无法修改FFmpeg内部各个变量的数值的,这种情况下只能通过输入“名称”和“值”这样的字符串,通过AVOption改变FFmpeg内部变量的值。由此可见,使用AVOption可以使FFmpeg更加适应多种多样的外部系统。
突然想到了JavaEE开发中也有这种类似的机制。互联网上只可以传输字符串,即是没有方法传输整形、浮点型这种的数据。而Java系统中却包含整形、浮点型等各种数据类型。因此开发JSP中的Servlet的时候经常需要将整数字符串手工转化成一个整型的变量。使用最多的一个函数就是Integer.parseInt()方法。例如下面代码可以将字符串“123”转化成整数123。
int a=Integer.parseInt("123");
而在使用JavaEE中的Struts2进行开发的时候,就不需要进行手动转换处理了。Struts2中包含了类似AVOption的这种数据类型自动转换机制,可以将互联网上收到的字符串“名称”和“值”的组合自动赋值给相应名称的变量。
由此发现了一个结论:编程语言之间真的是相通的!
现在回到AVOption。其实除了可以对FFmpeg常用结构体AVFormatContext,AVCodecContext等进行赋值之外,还可以对它们的私有数据priv_data进行赋值。这个字段里通常存储了各种编码器特有的结构体。而这些结构体的定义在FFmpeg的SDK中是找不到的。例如使用libx264进行编码的时候,通过AVCodecContext的priv_data字段可以对X264Context结构体中的变量进行赋值,设置preset,profile等。使用libx265进行编码的时候,通过AVCodecContext的priv_data字段可以对libx265Context结构体中的变量进行赋值,设置preset,tune等。
何为AVClass?
AVClass最主要的作用就是给结构体(例如AVFormatContext等)增加AVOption功能的支持。换句话说AVClass就是AVOption和目标结构体之间的“桥梁”。AVClass要求必须声明为目标结构体的第一个变量。
AVClass中有一个option数组用于存储目标结构体的所有的AVOption。举个例子,AVFormatContext结构体,AVClass和AVOption之间的关系如下图所示。
图中AVFormatContext结构体的第一个变量为AVClass类型的指针av_class,它在AVFormatContext结构体初始化的时候,被赋值指向了全局静态变量av_format_context_class结构体(定义位于libavformat\options.c)。而AVClass类型的av_format_context_class结构体中的option变量指向了全局静态数组avformat_options(定义位于libavformat\options_table.h)。
AVOption
下面开始从代码的角度记录AVOption。AVOption结构体的定义如下所示。
/** * AVOption */ typedef struct AVOption { const char *name; /** * short English help text * @todo What about other languages? */ const char *help; /** * The offset relative to the context structure where the option * value is stored. It should be 0 for named constants. */ int offset; enum AVOptionType type; /** * the default value for scalar options */ union { int64_t i64; double dbl; const char *str; /* TODO those are unused now */ AVRational q; } default_val; double min; ///< minimum valid value for the option double max; ///< maximum valid value for the option int flags; #define AV_OPT_FLAG_ENCODING_PARAM 1 ///< a generic parameter which can be set by the user for muxing or encoding #define AV_OPT_FLAG_DECODING_PARAM 2 ///< a generic parameter which can be set by the user for demuxing or decoding #if FF_API_OPT_TYPE_METADATA #define AV_OPT_FLAG_METADATA 4 ///< some data extracted or inserted into the file like title, comment, ... #endif #define AV_OPT_FLAG_AUDIO_PARAM 8 #define AV_OPT_FLAG_VIDEO_PARAM 16 #define AV_OPT_FLAG_SUBTITLE_PARAM 32 /** * The option is inteded for exporting values to the caller. */ #define AV_OPT_FLAG_EXPORT 64 /** * The option may not be set through the AVOptions API, only read. * This flag only makes sense when AV_OPT_FLAG_EXPORT is also set. */ #define AV_OPT_FLAG_READONLY 128 #define AV_OPT_FLAG_FILTERING_PARAM (1<<16) ///< a generic parameter which can be set by the user for filtering //FIXME think about enc-audio, ... style flags /** * The logical unit to which the option belongs. Non-constant * options and corresponding named constants share the same * unit. May be NULL. */ const char *unit; } AVOption;
下面简单解释一下AVOption的几个成员变量:
name:名称。
help:简短的帮助。
offset:选项相对结构体首部地址的偏移量(这个很重要)。
type:选项的类型。
default_val:选项的默认值。
min:选项的最小值。
max:选项的最大值。
flags:一些标记。
unit:该选项所属的逻辑单元,可以为空。
其中,default_val是一个union类型的变量,可以根据选项数据类型的不同,取int,double,char*,AVRational(表示分数)几种类型。type是一个AVOptionType类型的变量。AVOptionType是一个枚举类型,定义如下。
enum AVOptionType{ AV_OPT_TYPE_FLAGS, AV_OPT_TYPE_INT, AV_OPT_TYPE_INT64, AV_OPT_TYPE_DOUBLE, AV_OPT_TYPE_FLOAT, AV_OPT_TYPE_STRING, AV_OPT_TYPE_RATIONAL, AV_OPT_TYPE_BINARY, ///< offset must point to a pointer immediately followed by an int for the length AV_OPT_TYPE_DICT, AV_OPT_TYPE_CONST = 128, AV_OPT_TYPE_IMAGE_SIZE = MKBETAG('S','I','Z','E'), ///< offset must point to two consecutive integers AV_OPT_TYPE_PIXEL_FMT = MKBETAG('P','F','M','T'), AV_OPT_TYPE_SAMPLE_FMT = MKBETAG('S','F','M','T'), AV_OPT_TYPE_VIDEO_RATE = MKBETAG('V','R','A','T'), ///< offset must point to AVRational AV_OPT_TYPE_DURATION = MKBETAG('D','U','R',' '), AV_OPT_TYPE_COLOR = MKBETAG('C','O','L','R'), AV_OPT_TYPE_CHANNEL_LAYOUT = MKBETAG('C','H','L','A'), #if FF_API_OLD_AVOPTIONS FF_OPT_TYPE_FLAGS = 0, FF_OPT_TYPE_INT, FF_OPT_TYPE_INT64, FF_OPT_TYPE_DOUBLE, FF_OPT_TYPE_FLOAT, FF_OPT_TYPE_STRING, FF_OPT_TYPE_RATIONAL, FF_OPT_TYPE_BINARY, ///< offset must point to a pointer immediately followed by an int for the length FF_OPT_TYPE_CONST=128, #endif };
AVClass
AVClass中存储了AVOption类型的数组option,用于存储选项信息。AVClass有一个特点就是它必须位于其支持的结构体的第一个位置。例如,AVFormatContext和AVCodecContext都支持AVClass,观察它们结构体的定义可以发现他们结构体的第一个变量都是AVClass。截取一小段AVFormatContext的定义的开头部分,如下所示。
typedef struct AVFormatContext { /** * A class for logging and @ref avoptions. Set by avformat_alloc_context(). * Exports (de)muxer private options if they exist. */ const AVClass *av_class; /** * The input container format. * * Demuxing only, set by avformat_open_input(). */ struct AVInputFormat *iformat; /** * The output container format. * * Muxing only, must be set by the caller before avformat_write_header(). */ struct AVOutputFormat *oformat; //后文略
截取一小段AVCodecContext的定义的开头部分,如下所示。
typedef struct AVCodecContext { /** * information on struct for av_log * - set by avcodec_alloc_context3 */ const AVClass *av_class; int log_level_offset; enum AVMediaType codec_type; /* see AVMEDIA_TYPE_xxx */ const struct AVCodec *codec; //后文略
下面来看一下AVClass的定义,如下所示。
/** * Describe the class of an AVClass context structure. That is an * arbitrary struct of which the first field is a pointer to an * AVClass struct (e.g. AVCodecContext, AVFormatContext etc.). */ typedef struct AVClass { /** * The name of the class; usually it is the same name as the * context structure type to which the AVClass is associated. */ const char* class_name; /** * A pointer to a function which returns the name of a context * instance ctx associated with the class. */ const char* (*item_name)(void* ctx); /** * a pointer to the first option specified in the class if any or NULL * * @see av_set_default_options() */ const struct AVOption *option; /** * LIBAVUTIL_VERSION with which this structure was created. * This is used to allow fields to be added without requiring major * version bumps everywhere. */ int version; /** * Offset in the structure where log_level_offset is stored. * 0 means there is no such variable */ int log_level_offset_offset; /** * Offset in the structure where a pointer to the parent context for * logging is stored. For example a decoder could pass its AVCodecContext * to eval as such a parent context, which an av_log() implementation * could then leverage to display the parent context. * The offset can be NULL. */ int parent_log_context_offset; /** * Return next AVOptions-enabled child or NULL */ void* (*child_next)(void *obj, void *prev); /** * Return an AVClass corresponding to the next potential * AVOptions-enabled child. * * The difference between child_next and this is that * child_next iterates over _already existing_ objects, while * child_class_next iterates over _all possible_ children. */ const struct AVClass* (*child_class_next)(const struct AVClass *prev); /** * Category used for visualization (like color) * This is only set if the category is equal for all objects using this class. * available since version (51 << 16 | 56 << 8 | 100) */ AVClassCategory category; /** * Callback to return the category. * available since version (51 << 16 | 59 << 8 | 100) */ AVClassCategory (*get_category)(void* ctx); /** * Callback to return the supported/allowed ranges. * available since version (52.12) */ int (*query_ranges)(struct AVOptionRanges **, void *obj, const char *key, int flags); } AVClass;
下面简单解释一下AVClass的几个已经理解的成员变量:
class_name:AVClass名称。
item_name:函数,获取与AVClass相关联的结构体实例的名称。
option:AVOption类型的数组(最重要)。
version:完成该AVClass的时候的LIBAVUTIL_VERSION。
category:AVClass的类型,是一个类型为AVClassCategory的枚举型变量。
其中AVClassCategory定义如下。
typedef enum { AV_CLASS_CATEGORY_NA = 0, AV_CLASS_CATEGORY_INPUT, AV_CLASS_CATEGORY_OUTPUT, AV_CLASS_CATEGORY_MUXER, AV_CLASS_CATEGORY_DEMUXER, AV_CLASS_CATEGORY_ENCODER, AV_CLASS_CATEGORY_DECODER, AV_CLASS_CATEGORY_FILTER, AV_CLASS_CATEGORY_BITSTREAM_FILTER, AV_CLASS_CATEGORY_SWSCALER, AV_CLASS_CATEGORY_SWRESAMPLER, AV_CLASS_CATEGORY_DEVICE_VIDEO_OUTPUT = 40, AV_CLASS_CATEGORY_DEVICE_VIDEO_INPUT, AV_CLASS_CATEGORY_DEVICE_AUDIO_OUTPUT, AV_CLASS_CATEGORY_DEVICE_AUDIO_INPUT, AV_CLASS_CATEGORY_DEVICE_OUTPUT, AV_CLASS_CATEGORY_DEVICE_INPUT, AV_CLASS_CATEGORY_NB, ///< not part of ABI/API }AVClassCategory;
上面解释字段还是比较抽象的,下面通过具体的例子看一下AVClass这个结构体。我们看几个具体的例子:
- AVFormatContext中的AVClass
- AVCodecContext中的AVClass
- AVFrame中的AVClass
- 各种组件(libRTMP,libx264,libx265)里面特有的AVClass。
AVFormatContext
AVFormatContext 中的AVClass定义位于libavformat\options.c中,是一个名称为av_format_context_class的静态结构体。如下所示。
static const AVClass av_format_context_class = { .class_name = "AVFormatContext", .item_name = format_to_name, .option = avformat_options, .version = LIBAVUTIL_VERSION_INT, .child_next = format_child_next, .child_class_next = format_child_class_next, .category = AV_CLASS_CATEGORY_MUXER, .get_category = get_category, };
从源代码可以看出以下几点
(1)class_name
该AVClass名称是“AVFormatContext”。
(2)item_name
item_name指向一个函数format_to_name(),该函数定义如下所示。
static const char* format_to_name(void* ptr) { AVFormatContext* fc = (AVFormatContext*) ptr; if(fc->iformat) return fc->iformat->name; else if(fc->oformat) return fc->oformat->name; else return "NULL"; }
从函数的定义可以看出,如果AVFormatContext结构体中的AVInputFormat结构体不为空,则返回AVInputFormat的name,然后尝试返回AVOutputFormat的name,如果AVOutputFormat也为空,则返回“NULL”。
(3)option
option字段则指向一个元素个数很多的静态数组avformat_options。该数组单独定义于libavformat\options_table.h中。其中包含了AVFormatContext支持的所有的AVOption,如下所示。
/* * 雷霄骅 * leixiaohua1020@126.com * 中国传媒大学/数字电视技术 * http://blog.csdn.net/leixiaohua1020 * */ #ifndef AVFORMAT_OPTIONS_TABLE_H #define AVFORMAT_OPTIONS_TABLE_H #include <limits.h> #include "libavutil/opt.h" #include "avformat.h" #include "internal.h" #define OFFSET(x) offsetof(AVFormatContext,x) #define DEFAULT 0 //should be NAN but it does not work as it is not a constant in glibc as required by ANSI/ISO C //these names are too long to be readable #define E AV_OPT_FLAG_ENCODING_PARAM #define D AV_OPT_FLAG_DECODING_PARAM static const AVOption avformat_options[] = { {"avioflags", NULL, OFFSET(avio_flags), AV_OPT_TYPE_FLAGS, {.i64 = DEFAULT }, INT_MIN, INT_MAX, D|E, "avioflags"}, {"direct", "reduce buffering", 0, AV_OPT_TYPE_CONST, {.i64 = AVIO_FLAG_DIRECT }, INT_MIN, INT_MAX, D|E, "avioflags"}, {"probesize", "set probing size", OFFSET(probesize2), AV_OPT_TYPE_INT64, {.i64 = 5000000 }, 32, INT64_MAX, D}, {"formatprobesize", "number of bytes to probe file format", OFFSET(format_probesize), AV_OPT_TYPE_INT, {.i64 = PROBE_BUF_MAX}, 0, INT_MAX-1, D}, {"packetsize", "set packet size", OFFSET(packet_size), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, 0, INT_MAX, E}, {"fflags", NULL, OFFSET(flags), AV_OPT_TYPE_FLAGS, {.i64 = AVFMT_FLAG_FLUSH_PACKETS }, INT_MIN, INT_MAX, D|E, "fflags"}, {"flush_packets", "reduce the latency by flushing out packets immediately", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_FLUSH_PACKETS }, INT_MIN, INT_MAX, E, "fflags"}, {"ignidx", "ignore index", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_IGNIDX }, INT_MIN, INT_MAX, D, "fflags"}, {"genpts", "generate pts", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_GENPTS }, INT_MIN, INT_MAX, D, "fflags"}, {"nofillin", "do not fill in missing values that can be exactly calculated", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_NOFILLIN }, INT_MIN, INT_MAX, D, "fflags"}, {"noparse", "disable AVParsers, this needs nofillin too", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_NOPARSE }, INT_MIN, INT_MAX, D, "fflags"}, {"igndts", "ignore dts", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_IGNDTS }, INT_MIN, INT_MAX, D, "fflags"}, {"discardcorrupt", "discard corrupted frames", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_DISCARD_CORRUPT }, INT_MIN, INT_MAX, D, "fflags"}, {"sortdts", "try to interleave outputted packets by dts", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_SORT_DTS }, INT_MIN, INT_MAX, D, "fflags"}, {"keepside", "don't merge side data", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_KEEP_SIDE_DATA }, INT_MIN, INT_MAX, D, "fflags"}, {"latm", "enable RTP MP4A-LATM payload", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_MP4A_LATM }, INT_MIN, INT_MAX, E, "fflags"}, {"nobuffer", "reduce the latency introduced by optional buffering", 0, AV_OPT_TYPE_CONST, {.i64 = AVFMT_FLAG_NOBUFFER }, 0, INT_MAX, D, "fflags"}, {"seek2any", "allow seeking to non-keyframes on demuxer level when supported", OFFSET(seek2any), AV_OPT_TYPE_INT, {.i64 = 0 }, 0, 1, D}, {"bitexact", "do not write random/volatile data", 0, AV_OPT_TYPE_CONST, { .i64 = AVFMT_FLAG_BITEXACT }, 0, 0, E, "fflags" }, {"analyzeduration", "specify how many microseconds are analyzed to probe the input", OFFSET(max_analyze_duration2), AV_OPT_TYPE_INT64, {.i64 = 0 }, 0, INT64_MAX, D}, {"cryptokey", "decryption key", OFFSET(key), AV_OPT_TYPE_BINARY, {.dbl = 0}, 0, 0, D}, {"indexmem", "max memory used for timestamp index (per stream)", OFFSET(max_index_size), AV_OPT_TYPE_INT, {.i64 = 1<<20 }, 0, INT_MAX, D}, {"rtbufsize", "max memory used for buffering real-time frames", OFFSET(max_picture_buffer), AV_OPT_TYPE_INT, {.i64 = 3041280 }, 0, INT_MAX, D}, /* defaults to 1s of 15fps 352x288 YUYV422 video */ {"fdebug", "print specific debug info", OFFSET(debug), AV_OPT_TYPE_FLAGS, {.i64 = DEFAULT }, 0, INT_MAX, E|D, "fdebug"}, {"ts", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_FDEBUG_TS }, INT_MIN, INT_MAX, E|D, "fdebug"}, {"max_delay", "maximum muxing or demuxing delay in microseconds", OFFSET(max_delay), AV_OPT_TYPE_INT, {.i64 = -1 }, -1, INT_MAX, E|D}, {"start_time_realtime", "wall-clock time when stream begins (PTS==0)", OFFSET(start_time_realtime), AV_OPT_TYPE_INT64, {.i64 = AV_NOPTS_VALUE}, INT64_MIN, INT64_MAX, E}, {"fpsprobesize", "number of frames used to probe fps", OFFSET(fps_probe_size), AV_OPT_TYPE_INT, {.i64 = -1}, -1, INT_MAX-1, D}, {"audio_preload", "microseconds by which audio packets should be interleaved earlier", OFFSET(audio_preload), AV_OPT_TYPE_INT, {.i64 = 0}, 0, INT_MAX-1, E}, {"chunk_duration", "microseconds for each chunk", OFFSET(max_chunk_duration), AV_OPT_TYPE_INT, {.i64 = 0}, 0, INT_MAX-1, E}, {"chunk_size", "size in bytes for each chunk", OFFSET(max_chunk_size), AV_OPT_TYPE_INT, {.i64 = 0}, 0, INT_MAX-1, E}, /* this is a crutch for avconv, since it cannot deal with identically named options in different contexts. * to be removed when avconv is fixed */ {"f_err_detect", "set error detection flags (deprecated; use err_detect, save via avconv)", OFFSET(error_recognition), AV_OPT_TYPE_FLAGS, {.i64 = AV_EF_CRCCHECK }, INT_MIN, INT_MAX, D, "err_detect"}, {"err_detect", "set error detection flags", OFFSET(error_recognition), AV_OPT_TYPE_FLAGS, {.i64 = AV_EF_CRCCHECK }, INT_MIN, INT_MAX, D, "err_detect"}, {"crccheck", "verify embedded CRCs", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_CRCCHECK }, INT_MIN, INT_MAX, D, "err_detect"}, {"bitstream", "detect bitstream specification deviations", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_BITSTREAM }, INT_MIN, INT_MAX, D, "err_detect"}, {"buffer", "detect improper bitstream length", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_BUFFER }, INT_MIN, INT_MAX, D, "err_detect"}, {"explode", "abort decoding on minor error detection", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_EXPLODE }, INT_MIN, INT_MAX, D, "err_detect"}, {"ignore_err", "ignore errors", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_IGNORE_ERR }, INT_MIN, INT_MAX, D, "err_detect"}, {"careful", "consider things that violate the spec, are fast to check and have not been seen in the wild as errors", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_CAREFUL }, INT_MIN, INT_MAX, D, "err_detect"}, {"compliant", "consider all spec non compliancies as errors", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_COMPLIANT }, INT_MIN, INT_MAX, D, "err_detect"}, {"aggressive", "consider things that a sane encoder shouldn't do as an error", 0, AV_OPT_TYPE_CONST, {.i64 = AV_EF_AGGRESSIVE }, INT_MIN, INT_MAX, D, "err_detect"}, {"use_wallclock_as_timestamps", "use wallclock as timestamps", OFFSET(use_wallclock_as_timestamps), AV_OPT_TYPE_INT, {.i64 = 0}, 0, INT_MAX-1, D}, {"avoid_negative_ts", "shift timestamps so they start at 0", OFFSET(avoid_negative_ts), AV_OPT_TYPE_INT, {.i64 = -1}, -1, 2, E, "avoid_negative_ts"}, {"auto", "enabled when required by target format", 0, AV_OPT_TYPE_CONST, {.i64 = -1 }, INT_MIN, INT_MAX, E, "avoid_negative_ts"}, {"disabled", "do not change timestamps", 0, AV_OPT_TYPE_CONST, {.i64 = 0 }, INT_MIN, INT_MAX, E, "avoid_negative_ts"}, {"make_zero", "shift timestamps so they start at 0", 0, AV_OPT_TYPE_CONST, {.i64 = 2 }, INT_MIN, INT_MAX, E, "avoid_negative_ts"}, {"make_non_negative", "shift timestamps so they are non negative", 0, AV_OPT_TYPE_CONST, {.i64 = 1 }, INT_MIN, INT_MAX, E, "avoid_negative_ts"}, {"skip_initial_bytes", "set number of bytes to skip before reading header and frames", OFFSET(skip_initial_bytes), AV_OPT_TYPE_INT64, {.i64 = 0}, 0, INT64_MAX-1, D}, {"correct_ts_overflow", "correct single timestamp overflows", OFFSET(correct_ts_overflow), AV_OPT_TYPE_INT, {.i64 = 1}, 0, 1, D}, {"flush_packets", "enable flushing of the I/O context after each packet", OFFSET(flush_packets), AV_OPT_TYPE_INT, {.i64 = 1}, 0, 1, E}, {"metadata_header_padding", "set number of bytes to be written as padding in a metadata header", OFFSET(metadata_header_padding), AV_OPT_TYPE_INT, {.i64 = -1}, -1, INT_MAX, E}, {"output_ts_offset", "set output timestamp offset", OFFSET(output_ts_offset), AV_OPT_TYPE_DURATION, {.i64 = 0}, -INT64_MAX, INT64_MAX, E}, {"max_interleave_delta", "maximum buffering duration for interleaving", OFFSET(max_interleave_delta), AV_OPT_TYPE_INT64, { .i64 = 10000000 }, 0, INT64_MAX, E }, {"f_strict", "how strictly to follow the standards (deprecated; use strict, save via avconv)", OFFSET(strict_std_compliance), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, D|E, "strict"}, {"strict", "how strictly to follow the standards", OFFSET(strict_std_compliance), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, D|E, "strict"}, {"strict", "strictly conform to all the things in the spec no matter what the consequences", 0, AV_OPT_TYPE_CONST, {.i64 = FF_COMPLIANCE_STRICT }, INT_MIN, INT_MAX, D|E, "strict"}, {"normal", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = FF_COMPLIANCE_NORMAL }, INT_MIN, INT_MAX, D|E, "strict"}, {"experimental", "allow non-standardized experimental variants", 0, AV_OPT_TYPE_CONST, {.i64 = FF_COMPLIANCE_EXPERIMENTAL }, INT_MIN, INT_MAX, D|E, "strict"}, {"max_ts_probe", "maximum number of packets to read while waiting for the first timestamp", OFFSET(max_ts_probe), AV_OPT_TYPE_INT, { .i64 = 50 }, 0, INT_MAX, D }, {NULL}, }; #undef E #undef D #undef DEFAULT #undef OFFSET #endif /* AVFORMAT_OPTIONS_TABLE_H */
AVCodecContext
AVFormatContext 中的AVClass定义位于libavcodec\options.c中,是一个名称为av_codec_context_class的静态结构体。如下所示。
static const AVClass av_codec_context_class = { .class_name = "AVCodecContext", .item_name = context_to_name, .option = avcodec_options, .version = LIBAVUTIL_VERSION_INT, .log_level_offset_offset = offsetof(AVCodecContext, log_level_offset), .child_next = codec_child_next, .child_class_next = codec_child_class_next, .category = AV_CLASS_CATEGORY_ENCODER, .get_category = get_category, };
从源代码可以看出:
(1)class_name
该AVClass名称是“AVCodecContext”。
(2)item_name
item_name指向一个函数context_to_name (),该函数定义如下所示。
static const char* context_to_name(void* ptr) { AVCodecContext *avc= ptr; if(avc && avc->codec && avc->codec->name) return avc->codec->name; else return "NULL"; }
从函数的定义可以看出,如果AVCodecContext中的Codec结构体不为空,则返回Codec的name,否则返回“NULL”。
(3)category
option字段则指向一个元素个数极多的静态数组avcodec_options。该数组单独定义于libavcodec\options_table.h中。其中包含了AVCodecContext支持的所有的AVOption。由于该数组定义实在是太多了,在这里仅贴出它前面的一小部分。
/* * 雷霄骅 * leixiaohua1020@126.com * 中国传媒大学/数字电视技术 * http://blog.csdn.net/leixiaohua1020 * */ #ifndef AVCODEC_OPTIONS_TABLE_H #define AVCODEC_OPTIONS_TABLE_H #include <float.h> #include <limits.h> #include <stdint.h> #include "libavutil/opt.h" #include "avcodec.h" #include "version.h" #define OFFSET(x) offsetof(AVCodecContext,x) #define DEFAULT 0 //should be NAN but it does not work as it is not a constant in glibc as required by ANSI/ISO C //these names are too long to be readable #define V AV_OPT_FLAG_VIDEO_PARAM #define A AV_OPT_FLAG_AUDIO_PARAM #define S AV_OPT_FLAG_SUBTITLE_PARAM #define E AV_OPT_FLAG_ENCODING_PARAM #define D AV_OPT_FLAG_DECODING_PARAM #define AV_CODEC_DEFAULT_BITRATE 200*1000 static const AVOption avcodec_options[] = { {"b", "set bitrate (in bits/s)", OFFSET(bit_rate), AV_OPT_TYPE_INT, {.i64 = AV_CODEC_DEFAULT_BITRATE }, 0, INT_MAX, A|V|E}, {"ab", "set bitrate (in bits/s)", OFFSET(bit_rate), AV_OPT_TYPE_INT, {.i64 = 128*1000 }, 0, INT_MAX, A|E}, {"bt", "Set video bitrate tolerance (in bits/s). In 1-pass mode, bitrate tolerance specifies how far " "ratecontrol is willing to deviate from the target average bitrate value. This is not related " "to minimum/maximum bitrate. Lowering tolerance too much has an adverse effect on quality.", OFFSET(bit_rate_tolerance), AV_OPT_TYPE_INT, {.i64 = AV_CODEC_DEFAULT_BITRATE*20 }, 1, INT_MAX, V|E}, {"flags", NULL, OFFSET(flags), AV_OPT_TYPE_FLAGS, {.i64 = DEFAULT }, 0, UINT_MAX, V|A|S|E|D, "flags"}, {"unaligned", "allow decoders to produce unaligned output", 0, AV_OPT_TYPE_CONST, { .i64 = CODEC_FLAG_UNALIGNED }, INT_MIN, INT_MAX, V | D, "flags" }, {"mv4", "use four motion vectors per macroblock (MPEG-4)", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_4MV }, INT_MIN, INT_MAX, V|E, "flags"}, {"qpel", "use 1/4-pel motion compensation", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_QPEL }, INT_MIN, INT_MAX, V|E, "flags"}, {"loop", "use loop filter", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_LOOP_FILTER }, INT_MIN, INT_MAX, V|E, "flags"}, {"qscale", "use fixed qscale", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_QSCALE }, INT_MIN, INT_MAX, 0, "flags"}, #if FF_API_GMC {"gmc", "use gmc", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_GMC }, INT_MIN, INT_MAX, V|E, "flags"}, #endif #if FF_API_MV0 {"mv0", "always try a mb with mv=<0,0>", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_MV0 }, INT_MIN, INT_MAX, V|E, "flags"}, #endif #if FF_API_INPUT_PRESERVED {"input_preserved", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_INPUT_PRESERVED }, INT_MIN, INT_MAX, 0, "flags"}, #endif {"pass1", "use internal 2-pass ratecontrol in first pass mode", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_PASS1 }, INT_MIN, INT_MAX, 0, "flags"}, {"pass2", "use internal 2-pass ratecontrol in second pass mode", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_PASS2 }, INT_MIN, INT_MAX, 0, "flags"}, {"gray", "only decode/encode grayscale", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_GRAY }, INT_MIN, INT_MAX, V|E|D, "flags"}, #if FF_API_EMU_EDGE {"emu_edge", "do not draw edges", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_EMU_EDGE }, INT_MIN, INT_MAX, 0, "flags"}, #endif {"psnr", "error[?] variables will be set during encoding", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_PSNR }, INT_MIN, INT_MAX, V|E, "flags"}, {"truncated", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_TRUNCATED }, INT_MIN, INT_MAX, 0, "flags"}, #if FF_API_NORMALIZE_AQP {"naq", "normalize adaptive quantization", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_NORMALIZE_AQP }, INT_MIN, INT_MAX, V|E, "flags"}, #endif {"ildct", "use interlaced DCT", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_INTERLACED_DCT }, INT_MIN, INT_MAX, V|E, "flags"}, {"low_delay", "force low delay", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_LOW_DELAY }, INT_MIN, INT_MAX, V|D|E, "flags"}, {"global_header", "place global headers in extradata instead of every keyframe", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_GLOBAL_HEADER }, INT_MIN, INT_MAX, V|A|E, "flags"}, {"bitexact", "use only bitexact functions (except (I)DCT)", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_BITEXACT }, INT_MIN, INT_MAX, A|V|S|D|E, "flags"}, {"aic", "H.263 advanced intra coding / MPEG-4 AC prediction", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_AC_PRED }, INT_MIN, INT_MAX, V|E, "flags"}, {"ilme", "interlaced motion estimation", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_INTERLACED_ME }, INT_MIN, INT_MAX, V|E, "flags"}, {"cgop", "closed GOP", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_CLOSED_GOP }, INT_MIN, INT_MAX, V|E, "flags"}, {"output_corrupt", "Output even potentially corrupted frames", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG_OUTPUT_CORRUPT }, INT_MIN, INT_MAX, V|D, "flags"}, {"fast", "allow non-spec-compliant speedup tricks", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG2_FAST }, INT_MIN, INT_MAX, V|E, "flags2"}, {"noout", "skip bitstream encoding", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG2_NO_OUTPUT }, INT_MIN, INT_MAX, V|E, "flags2"}, {"ignorecrop", "ignore cropping information from sps", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG2_IGNORE_CROP }, INT_MIN, INT_MAX, V|D, "flags2"}, {"local_header", "place global headers at every keyframe instead of in extradata", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG2_LOCAL_HEADER }, INT_MIN, INT_MAX, V|E, "flags2"}, {"chunks", "Frame data might be split into multiple chunks", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG2_CHUNKS }, INT_MIN, INT_MAX, V|D, "flags2"}, {"showall", "Show all frames before the first keyframe", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG2_SHOW_ALL }, INT_MIN, INT_MAX, V|D, "flags2"}, {"export_mvs", "export motion vectors through frame side data", 0, AV_OPT_TYPE_CONST, {.i64 = CODEC_FLAG2_EXPORT_MVS}, INT_MIN, INT_MAX, V|D, "flags2"}, {"me_method", "set motion estimation method", OFFSET(me_method), AV_OPT_TYPE_INT, {.i64 = ME_EPZS }, INT_MIN, INT_MAX, V|E, "me_method"}, {"zero", "zero motion estimation (fastest)", 0, AV_OPT_TYPE_CONST, {.i64 = ME_ZERO }, INT_MIN, INT_MAX, V|E, "me_method" }, {"full", "full motion estimation (slowest)", 0, AV_OPT_TYPE_CONST, {.i64 = ME_FULL }, INT_MIN, INT_MAX, V|E, "me_method" }, {"epzs", "EPZS motion estimation (default)", 0, AV_OPT_TYPE_CONST, {.i64 = ME_EPZS }, INT_MIN, INT_MAX, V|E, "me_method" }, {"esa", "esa motion estimation (alias for full)", 0, AV_OPT_TYPE_CONST, {.i64 = ME_FULL }, INT_MIN, INT_MAX, V|E, "me_method" }, {"tesa", "tesa motion estimation", 0, AV_OPT_TYPE_CONST, {.i64 = ME_TESA }, INT_MIN, INT_MAX, V|E, "me_method" }, {"dia", "diamond motion estimation (alias for EPZS)", 0, AV_OPT_TYPE_CONST, {.i64 = ME_EPZS }, INT_MIN, INT_MAX, V|E, "me_method" }, {"log", "log motion estimation", 0, AV_OPT_TYPE_CONST, {.i64 = ME_LOG }, INT_MIN, INT_MAX, V|E, "me_method" }, {"phods", "phods motion estimation", 0, AV_OPT_TYPE_CONST, {.i64 = ME_PHODS }, INT_MIN, INT_MAX, V|E, "me_method" }, {"x1", "X1 motion estimation", 0, AV_OPT_TYPE_CONST, {.i64 = ME_X1 }, INT_MIN, INT_MAX, V|E, "me_method" }, {"hex", "hex motion estimation", 0, AV_OPT_TYPE_CONST, {.i64 = ME_HEX }, INT_MIN, INT_MAX, V|E, "me_method" }, {"umh", "umh motion estimation", 0, AV_OPT_TYPE_CONST, {.i64 = ME_UMH }, INT_MIN, INT_MAX, V|E, "me_method" }, {"iter", "iter motion estimation", 0, AV_OPT_TYPE_CONST, {.i64 = ME_ITER }, INT_MIN, INT_MAX, V|E, "me_method" }, {"extradata_size", NULL, OFFSET(extradata_size), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX}, {"time_base", NULL, OFFSET(time_base), AV_OPT_TYPE_RATIONAL, {.dbl = 0}, INT_MIN, INT_MAX}, {"g", "set the group of picture (GOP) size", OFFSET(gop_size), AV_OPT_TYPE_INT, {.i64 = 12 }, INT_MIN, INT_MAX, V|E}, {"ar", "set audio sampling rate (in Hz)", OFFSET(sample_rate), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, A|D|E}, {"ac", "set number of audio channels", OFFSET(channels), AV_OPT_TYPE_INT, {.i64 = DEFAULT }, INT_MIN, INT_MAX, A|D|E},
AVFrame
AVFrame 中的AVClass定义位于libavcodec\options.c中,是一个名称为av_frame_class的静态结构体。如下所示。
static const AVClass av_frame_class = { .class_name = "AVFrame", .item_name = NULL, .option = frame_options, .version = LIBAVUTIL_VERSION_INT, };
option字段则指向一个元素个数极多的静态数组frame_options。frame_options定义如下所示。
static const AVOption frame_options[]={ {"best_effort_timestamp", "", FOFFSET(best_effort_timestamp), AV_OPT_TYPE_INT64, {.i64 = AV_NOPTS_VALUE }, INT64_MIN, INT64_MAX, 0}, {"pkt_pos", "", FOFFSET(pkt_pos), AV_OPT_TYPE_INT64, {.i64 = -1 }, INT64_MIN, INT64_MAX, 0}, {"pkt_size", "", FOFFSET(pkt_size), AV_OPT_TYPE_INT64, {.i64 = -1 }, INT64_MIN, INT64_MAX, 0}, {"sample_aspect_ratio", "", FOFFSET(sample_aspect_ratio), AV_OPT_TYPE_RATIONAL, {.dbl = 0 }, 0, INT_MAX, 0}, {"width", "", FOFFSET(width), AV_OPT_TYPE_INT, {.i64 = 0 }, 0, INT_MAX, 0}, {"height", "", FOFFSET(height), AV_OPT_TYPE_INT, {.i64 = 0 }, 0, INT_MAX, 0}, {"format", "", FOFFSET(format), AV_OPT_TYPE_INT, {.i64 = -1 }, 0, INT_MAX, 0}, {"channel_layout", "", FOFFSET(channel_layout), AV_OPT_TYPE_INT64, {.i64 = 0 }, 0, INT64_MAX, 0}, {"sample_rate", "", FOFFSET(sample_rate), AV_OPT_TYPE_INT, {.i64 = 0 }, 0, INT_MAX, 0}, {NULL}, };
可以看出AVFrame的选项数组中包含了“width”,“height”这类用于视频帧的选项,以及“channel_layout”,“sample_rate”这类用于音频帧的选项。
各种组件特有的AVClass
除了FFmpeg中通用的AVFormatContext,AVCodecContext,AVFrame这类的结构体之外,每种特定的组件也包含自己的AVClass。下面举例几个。
LibRTMP
libRTMP中根据协议类型的不同定义了多种的AVClass。由于这些AVClass除了名字不一样之外,其他的字段一模一样,所以AVClass的声明写成了一个名称为RTMP_CLASS的宏。
#define RTMP_CLASS(flavor)\ static const AVClass lib ## flavor ## _class = {\ .class_name = "lib" #flavor " protocol",\ .item_name = av_default_item_name,\ .option = options,\ .version = LIBAVUTIL_VERSION_INT,\ };
而后定义了多种AVCLass:
RTMP_CLASS(rtmp) RTMP_CLASS(rtmpt) RTMP_CLASS(rtmpe) RTMP_CLASS(rtmpte) RTMP_CLASS(rtmps)
这些AVClass的option字段指向的数组是一样的,如下所示。
static const AVOption options[] = { {"rtmp_app", "Name of application to connect to on the RTMP server", OFFSET(app), AV_OPT_TYPE_STRING, {.str = NULL }, 0, 0, DEC|ENC}, {"rtmp_buffer", "Set buffer time in milliseconds. The default is 3000.", OFFSET(client_buffer_time), AV_OPT_TYPE_STRING, {.str = "3000"}, 0, 0, DEC|ENC}, {"rtmp_conn", "Append arbitrary AMF data to the Connect message", OFFSET(conn), AV_OPT_TYPE_STRING, {.str = NULL }, 0, 0, DEC|ENC}, {"rtmp_flashver", "Version of the Flash plugin used to run the SWF player.", OFFSET(flashver), AV_OPT_TYPE_STRING, {.str = NULL }, 0, 0, DEC|ENC}, {"rtmp_live", "Specify that the media is a live stream.", OFFSET(live), AV_OPT_TYPE_INT, {.i64 = 0}, INT_MIN, INT_MAX, DEC, "rtmp_live"}, {"any", "both", 0, AV_OPT_TYPE_CONST, {.i64 = -2}, 0, 0, DEC, "rtmp_live"}, {"live", "live stream", 0, AV_OPT_TYPE_CONST, {.i64 = -1}, 0, 0, DEC, "rtmp_live"}, {"recorded", "recorded stream", 0, AV_OPT_TYPE_CONST, {.i64 = 0}, 0, 0, DEC, "rtmp_live"}, {"rtmp_pageurl", "URL of the web page in which the media was embedded. By default no value will be sent.", OFFSET(pageurl), AV_OPT_TYPE_STRING, {.str = NULL }, 0, 0, DEC}, {"rtmp_playpath", "Stream identifier to play or to publish", OFFSET(playpath), AV_OPT_TYPE_STRING, {.str = NULL }, 0, 0, DEC|ENC}, {"rtmp_subscribe", "Name of live stream to subscribe to. Defaults to rtmp_playpath.", OFFSET(subscribe), AV_OPT_TYPE_STRING, {.str = NULL }, 0, 0, DEC}, {"rtmp_swfurl", "URL of the SWF player. By default no value will be sent", OFFSET(swfurl), AV_OPT_TYPE_STRING, {.str = NULL }, 0, 0, DEC|ENC}, {"rtmp_swfverify", "URL to player swf file, compute hash/size automatically. (unimplemented)", OFFSET(swfverify), AV_OPT_TYPE_STRING, {.str = NULL }, 0, 0, DEC}, {"rtmp_tcurl", "URL of the target stream. Defaults to proto://host[:port]/app.", OFFSET(tcurl), AV_OPT_TYPE_STRING, {.str = NULL }, 0, 0, DEC|ENC}, { NULL }, };
Libx264
Libx264的AVClass定义如下所示。
static const AVClass x264_class = { .class_name = "libx264", .item_name = av_default_item_name, .option = options, .version = LIBAVUTIL_VERSION_INT, };
其中option字段指向的数组定义如下所示。这些option的使用频率还是比较高的。
static const AVOption options[] = { { "preset", "Set the encoding preset (cf. x264 --fullhelp)", OFFSET(preset), AV_OPT_TYPE_STRING, { .str = "medium" }, 0, 0, VE}, { "tune", "Tune the encoding params (cf. x264 --fullhelp)", OFFSET(tune), AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE}, { "profile", "Set profile restrictions (cf. x264 --fullhelp) ", OFFSET(profile), AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE}, { "fastfirstpass", "Use fast settings when encoding first pass", OFFSET(fastfirstpass), AV_OPT_TYPE_INT, { .i64 = 1 }, 0, 1, VE}, {"level", "Specify level (as defined by Annex A)", OFFSET(level), AV_OPT_TYPE_STRING, {.str=NULL}, 0, 0, VE}, {"passlogfile", "Filename for 2 pass stats", OFFSET(stats), AV_OPT_TYPE_STRING, {.str=NULL}, 0, 0, VE}, {"wpredp", "Weighted prediction for P-frames", OFFSET(wpredp), AV_OPT_TYPE_STRING, {.str=NULL}, 0, 0, VE}, {"x264opts", "x264 options", OFFSET(x264opts), AV_OPT_TYPE_STRING, {.str=NULL}, 0, 0, VE}, { "crf", "Select the quality for constant quality mode", OFFSET(crf), AV_OPT_TYPE_FLOAT, {.dbl = -1 }, -1, FLT_MAX, VE }, { "crf_max", "In CRF mode, prevents VBV from lowering quality beyond this point.",OFFSET(crf_max), AV_OPT_TYPE_FLOAT, {.dbl = -1 }, -1, FLT_MAX, VE }, { "qp", "Constant quantization parameter rate control method",OFFSET(cqp), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, VE }, { "aq-mode", "AQ method", OFFSET(aq_mode), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, VE, "aq_mode"}, { "none", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = X264_AQ_NONE}, INT_MIN, INT_MAX, VE, "aq_mode" }, { "variance", "Variance AQ (complexity mask)", 0, AV_OPT_TYPE_CONST, {.i64 = X264_AQ_VARIANCE}, INT_MIN, INT_MAX, VE, "aq_mode" }, { "autovariance", "Auto-variance AQ (experimental)", 0, AV_OPT_TYPE_CONST, {.i64 = X264_AQ_AUTOVARIANCE}, INT_MIN, INT_MAX, VE, "aq_mode" }, { "aq-strength", "AQ strength. Reduces blocking and blurring in flat and textured areas.", OFFSET(aq_strength), AV_OPT_TYPE_FLOAT, {.dbl = -1}, -1, FLT_MAX, VE}, { "psy", "Use psychovisual optimizations.", OFFSET(psy), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 1, VE }, { "psy-rd", "Strength of psychovisual optimization, in <psy-rd>:<psy-trellis> format.", OFFSET(psy_rd), AV_OPT_TYPE_STRING, {0 }, 0, 0, VE}, { "rc-lookahead", "Number of frames to look ahead for frametype and ratecontrol", OFFSET(rc_lookahead), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, VE }, { "weightb", "Weighted prediction for B-frames.", OFFSET(weightb), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 1, VE }, { "weightp", "Weighted prediction analysis method.", OFFSET(weightp), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, VE, "weightp" }, { "none", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = X264_WEIGHTP_NONE}, INT_MIN, INT_MAX, VE, "weightp" }, { "simple", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = X264_WEIGHTP_SIMPLE}, INT_MIN, INT_MAX, VE, "weightp" }, { "smart", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = X264_WEIGHTP_SMART}, INT_MIN, INT_MAX, VE, "weightp" }, { "ssim", "Calculate and print SSIM stats.", OFFSET(ssim), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 1, VE }, { "intra-refresh", "Use Periodic Intra Refresh instead of IDR frames.",OFFSET(intra_refresh),AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 1, VE }, { "bluray-compat", "Bluray compatibility workarounds.", OFFSET(bluray_compat) ,AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 1, VE }, { "b-bias", "Influences how often B-frames are used", OFFSET(b_bias), AV_OPT_TYPE_INT, { .i64 = INT_MIN}, INT_MIN, INT_MAX, VE }, { "b-pyramid", "Keep some B-frames as references.", OFFSET(b_pyramid), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, VE, "b_pyramid" }, { "none", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = X264_B_PYRAMID_NONE}, INT_MIN, INT_MAX, VE, "b_pyramid" }, { "strict", "Strictly hierarchical pyramid", 0, AV_OPT_TYPE_CONST, {.i64 = X264_B_PYRAMID_STRICT}, INT_MIN, INT_MAX, VE, "b_pyramid" }, { "normal", "Non-strict (not Blu-ray compatible)", 0, AV_OPT_TYPE_CONST, {.i64 = X264_B_PYRAMID_NORMAL}, INT_MIN, INT_MAX, VE, "b_pyramid" }, { "mixed-refs", "One reference per partition, as opposed to one reference per macroblock", OFFSET(mixed_refs), AV_OPT_TYPE_INT, { .i64 = -1}, -1, 1, VE }, { "8x8dct", "High profile 8x8 transform.", OFFSET(dct8x8), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 1, VE}, { "fast-pskip", NULL, OFFSET(fast_pskip), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 1, VE}, { "aud", "Use access unit delimiters.", OFFSET(aud), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 1, VE}, { "mbtree", "Use macroblock tree ratecontrol.", OFFSET(mbtree), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 1, VE}, { "deblock", "Loop filter parameters, in <alpha:beta> form.", OFFSET(deblock), AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE}, { "cplxblur", "Reduce fluctuations in QP (before curve compression)", OFFSET(cplxblur), AV_OPT_TYPE_FLOAT, {.dbl = -1 }, -1, FLT_MAX, VE}, { "partitions", "A comma-separated list of partitions to consider. " "Possible values: p8x8, p4x4, b8x8, i8x8, i4x4, none, all", OFFSET(partitions), AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE}, { "direct-pred", "Direct MV prediction mode", OFFSET(direct_pred), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, VE, "direct-pred" }, { "none", NULL, 0, AV_OPT_TYPE_CONST, { .i64 = X264_DIRECT_PRED_NONE }, 0, 0, VE, "direct-pred" }, { "spatial", NULL, 0, AV_OPT_TYPE_CONST, { .i64 = X264_DIRECT_PRED_SPATIAL }, 0, 0, VE, "direct-pred" }, { "temporal", NULL, 0, AV_OPT_TYPE_CONST, { .i64 = X264_DIRECT_PRED_TEMPORAL }, 0, 0, VE, "direct-pred" }, { "auto", NULL, 0, AV_OPT_TYPE_CONST, { .i64 = X264_DIRECT_PRED_AUTO }, 0, 0, VE, "direct-pred" }, { "slice-max-size","Limit the size of each slice in bytes", OFFSET(slice_max_size),AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, VE }, { "stats", "Filename for 2 pass stats", OFFSET(stats), AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE }, { "nal-hrd", "Signal HRD information (requires vbv-bufsize; " "cbr not allowed in .mp4)", OFFSET(nal_hrd), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, VE, "nal-hrd" }, { "none", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = X264_NAL_HRD_NONE}, INT_MIN, INT_MAX, VE, "nal-hrd" }, { "vbr", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = X264_NAL_HRD_VBR}, INT_MIN, INT_MAX, VE, "nal-hrd" }, { "cbr", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = X264_NAL_HRD_CBR}, INT_MIN, INT_MAX, VE, "nal-hrd" }, { "avcintra-class","AVC-Intra class 50/100/200", OFFSET(avcintra_class),AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 200 , VE}, { "x264-params", "Override the x264 configuration using a :-separated list of key=value parameters", OFFSET(x264_params), AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE }, { NULL }, };
Libx265
Libx265的AVClass定义如下所示。
static const AVClass class = { .class_name = "libx265", .item_name = av_default_item_name, .option = options, .version = LIBAVUTIL_VERSION_INT, };
其中option字段指向的数组定义如下所示。
static const AVOption options[] = { { "preset", "set the x265 preset", OFFSET(preset), AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE }, { "tune", "set the x265 tune parameter", OFFSET(tune), AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE }, { "x265-params", "set the x265 configuration using a :-separated list of key=value parameters", OFFSET(x265_opts), AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE }, { NULL } };
官方代码中有关AVClass和AVOption的示例
官方代码中给出了一小段示例代码,演示了如何给一个普通的结构体添加AVOption的支持。如下所示。
typedef struct test_struct { AVClass *class; int int_opt; char str_opt; uint8_t bin_opt; int bin_len; } test_struct; static const AVOption test_options[] = { { "test_int", "This is a test option of int type.", offsetof(test_struct, int_opt), AV_OPT_TYPE_INT, { .i64 = -1 }, INT_MIN, INT_MAX }, { "test_str", "This is a test option of string type.", offsetof(test_struct, str_opt), AV_OPT_TYPE_STRING }, { "test_bin", "This is a test option of binary type.", offsetof(test_struct, bin_opt), AV_OPT_TYPE_BINARY }, { NULL }, }; static const AVClass test_class = { .class_name = "test class", .item_name = av_default_item_name, .option = test_options, .version = LIBAVUTIL_VERSION_INT, };
AVClass有关的API
与AVClass相关的API很少。AVFormatContext提供了一个获取当前AVClass的函数avformat_get_class()。它的代码很简单,直接返回全局静态变量av_format_context_class。定义如下所示。
const AVClass *avformat_get_class(void) { return &av_format_context_class; }
同样,AVCodecContext也提供了一个获取当前AVClass的函数avcodec_get_class()。它直接返回静态变量av_codec_context_class。定义如下所示。
const AVClass *avcodec_get_class(void) { return &av_codec_context_class; }
至此FFmpeg的AVClass就基本上分析完毕了。下篇文章具体分析AVOption。
雷霄骅
leixiaohua1020@126.com
http://blog.csdn.net/leixiaohua1020
FFmpeg源代码简单分析:结构体成员管理系统-AVClass的更多相关文章
- FFmpeg源代码简单分析:结构体成员管理系统-AVOption
===================================================== FFmpeg的库函数源代码分析文章列表: [架构图] FFmpeg源代码结构图 - 解码 F ...
- FFmpeg源码简单分析:结构体成员管理系统-AVOption
===================================================== FFmpeg的库函数源码分析文章列表: [架构图] FFmpeg源码结构图 - 解码 FFm ...
- FFmpeg源代码简单分析:常见结构体的初始化和销毁(AVFormatContext,AVFrame等)
===================================================== FFmpeg的库函数源代码分析文章列表: [架构图] FFmpeg源代码结构图 - 解码 F ...
- [转载] FFmpeg源代码简单分析:常见结构体的初始化和销毁(AVFormatContext,AVFrame等)
===================================================== FFmpeg的库函数源代码分析文章列表: [架构图] FFmpeg源代码结构图 - 解码 F ...
- FFmpeg源代码简单分析:libavdevice的gdigrab
===================================================== FFmpeg的库函数源代码分析文章列表: [架构图] FFmpeg源代码结构图 - 解码 F ...
- FFmpeg源代码简单分析:libavdevice的avdevice_register_all()
===================================================== FFmpeg的库函数源代码分析文章列表: [架构图] FFmpeg源代码结构图 - 解码 F ...
- FFmpeg源代码简单分析:configure
===================================================== FFmpeg的库函数源代码分析文章列表: [架构图] FFmpeg源代码结构图 - 解码 F ...
- FFmpeg源代码简单分析:makefile
===================================================== FFmpeg的库函数源代码分析文章列表: [架构图] FFmpeg源代码结构图 - 解码 F ...
- FFmpeg源代码简单分析:libswscale的sws_scale()
===================================================== FFmpeg的库函数源代码分析文章列表: [架构图] FFmpeg源代码结构图 - 解码 F ...
随机推荐
- 例10-12 *uva1637(概率dp)
题意:36张扑克,平分成9摞,两张数字一样的可以拿走,每次随机拿两张,问能拿光的概率. 思路: 直接用搜索,表示出每摞剩余的牌数,然后利用全概率公式即可(P(A) = p(A|b1)*p(b1)+.. ...
- [bzoj4236]JOIOJI
来自FallDream的博客,未经允许,请勿转载,谢谢. JOIOJI桑是JOI君的叔叔.“JOIOJI”这个名字是由“J.O.I”三个字母各两个构成的. 最近,JOIOJI桑有了一个孩子.JOIOJ ...
- [3.24校内训练赛by hzwer]
来自FallDream的博客,未经允许,请勿转载,谢谢. ----------------------------------------------------------------------- ...
- 使用C# (.NET Core) 实现状态设计模式 (State Pattern)
本文的概念性内容来自深入浅出设计模式一书 项目需求 这是一个糖果机的需求图. 它有四种状态, 分别是图中的四个圆圈: No Quarter: 无硬币 Has Quater 有硬币 Gumball So ...
- mooc-python语言语法week3-6
week3 1.类型的概念:程序编程不允许有歧义的数据类型存在,所以对数据进行了划分,python语言类型分为,数字类型.字符串类型.元组类型.列表类型.文件类型.字典类型. i:数字类型: pyth ...
- Mysql锁机制--乐观锁 & 悲观锁
Mysql 系列文章主页 =============== 从 这篇 文章中,我们知道 Mysql 并发事务会引起更新丢失问题,解决办法是锁.所以本文将对锁(乐观锁.悲观锁)进行分析. 第一部分 悲观锁 ...
- Jenkins构建时间Poll Scm的设置
每15分钟构建一次:H/15 * * * * 或*/15 * * * * 每天8点构建一次:0 8 * * * 每天8点~17点,两小时构建一次:0 8-17/2 * * * 周一到周五,8点~1 ...
- Django笔记--视图
URLconf 在settings.py文件中通过ROOT_URLCONF指定根级url的配置 urlpatterns是一个url()实例的列表 一个url()对象包括: 正则表达式 视图函数 名称n ...
- 利用Python进行数据分析——重要的Python库介绍
利用Python进行数据分析--重要的Python库介绍 一.NumPy 用于数组执行元素级计算及直接对数组执行数学运算 线性代数运算.傅里叶运算.随机数的生成 用于C/C++等代码的集成 二.pan ...
- ng-book札记——HTTP
Angular拥有自己的HTTP库,可以用于调用外部API. 在JavaScript世界里有三种方式可以实现异步请求,Callback,Promise与Observable.Angular倾向于使用O ...