最简单的基于FFmpeg的内存读写的例子：内存转码器

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最简单的基于FFmpeg的内存读写的例子系列文章列表：

最简单的基于FFmpeg的内存读写的例子：内存播放器

最简单的基于FFmpeg的内存读写的例子：内存转码器

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上篇文章记录了一个基于FFmpeg的内存播放器，可以使用FFmpeg读取并播放内存中的数据。这篇文章记录一个基于FFmpeg的内存转码器。该转码器可以使用FFmpeg读取内存中的数据，转码为H.264之后再将数据输出到内存。

关于如何从内存读取数据，以及如何将数据输出到内存，可以参考文章：

ffmpeg 从内存中读取数据(或将数据输出到内存)

FFmpeg读写内存的关键点有2个：
1.       初始化自定义的AVIOContext，指定自定义的回调函数。
2.       自己写回调函数。注意函数的参数和返回值（尤其是返回值）。
 
 
转码实际上就是解码和编码的结合。该方面的知识可以参考文章：

解码：100行代码实现最简单的基于FFMPEG+SDL的视频播放器（SDL1.x）

编码：最简单的基于FFMPEG的视频编码器（YUV编码为H.264）

转码：最简单的基于FFMPEG的转码程序

流程

程序的流程图如下图所示。从图中可以看出，首先分别初始化了输入和输出的AVFormatContext。然后首先解码输入的AVPacket，得到存储像素数据（YUV420P格式）的AVFrame，然后编码AVFrame为H.264的AVPacket，最后将编码后的AVPacket输出。

代码

下面直接贴上代码：
 
 

/**
 * 最简单的基于FFmpeg的内存读写例子（内存转码器）
 * Simplest FFmpeg mem Transcoder
 *
 * 雷霄骅，张晖
 * leixiaohua1020@126.com
 * 中国传媒大学/数字电视技术
 * Communication University of China / Digital TV Technology
 * http://blog.csdn.net/leixiaohua1020
 *
 * 本程序实现了任意格式视频数据（例如MPEG2）转码为H.264码流数据。
 * 本程序并不是对文件进行处理，而是对内存中的视频数据进行处理。
 * 它从内存读取数据，并且将转码后的数据输出到内存中。
 * 是最简单的使用FFmpeg读写内存的例子。
 *
 * This software convert video bitstream (Such as MPEG2) to H.264
 * bitstream. It read video bitstream from memory (not from a file),
 * convert it to H.264 bitstream, and finally output to another memory.
 * It's the simplest example to use FFmpeg to read (or write) from
 * memory.
 *
 */
#include <stdio.h>

extern "C"
{
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/avutil.h"
#include "libavutil/opt.h"
#include "libavutil/pixdesc.h"
};

FILE *fp_open;
FILE *fp_write;

//Read File
int read_buffer(void *opaque, uint8_t *buf, int buf_size){
	if(!feof(fp_open)){
		int true_size=fread(buf,1,buf_size,fp_open);
		return true_size;
	}else{
		return -1;
	}
}

//Write File
int write_buffer(void *opaque, uint8_t *buf, int buf_size){
	if(!feof(fp_write)){
		int true_size=fwrite(buf,1,buf_size,fp_write);
		return true_size;
	}else{
		return -1;
	}
}

int flush_encoder(AVFormatContext *fmt_ctx,unsigned int stream_index)
{
    int ret;
    int got_frame;
	AVPacket enc_pkt;
    if (!(fmt_ctx->streams[stream_index]->codec->codec->capabilities &
                CODEC_CAP_DELAY))
        return 0;
    while (1) {
        av_log(NULL, AV_LOG_INFO, "Flushing stream #%u encoder\n", stream_index);
        //ret = encode_write_frame(NULL, stream_index, &got_frame);
        enc_pkt.data = NULL;
		enc_pkt.size = 0;
		av_init_packet(&enc_pkt);
		ret = avcodec_encode_video2 (fmt_ctx->streams[stream_index]->codec, &enc_pkt,
				NULL, &got_frame);
		av_frame_free(NULL);
		if (ret < 0)
			break;
		if (!got_frame)
		{ret=0;break;}
		/* prepare packet for muxing */
		enc_pkt.stream_index = stream_index;
		enc_pkt.dts = av_rescale_q_rnd(enc_pkt.dts,
				fmt_ctx->streams[stream_index]->codec->time_base,
				fmt_ctx->streams[stream_index]->time_base,
				(AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
		enc_pkt.pts = av_rescale_q_rnd(enc_pkt.pts,
				fmt_ctx->streams[stream_index]->codec->time_base,
				fmt_ctx->streams[stream_index]->time_base,
				(AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
		enc_pkt.duration = av_rescale_q(enc_pkt.duration,
				fmt_ctx->streams[stream_index]->codec->time_base,
				fmt_ctx->streams[stream_index]->time_base);
		av_log(NULL, AV_LOG_DEBUG, "Muxing frame\n");
		/* mux encoded frame */
		ret = av_write_frame(fmt_ctx, &enc_pkt);
		if (ret < 0)
            break;
    }
    return ret;
}

int main(int argc, char* argv[])
{
	int ret;
	AVFormatContext* ifmt_ctx=NULL;
	AVFormatContext* ofmt_ctx=NULL;
	AVPacket packet,enc_pkt;
	AVFrame *frame = NULL;
	enum AVMediaType type;
	unsigned int stream_index;
	unsigned int i=0;
	int got_frame,enc_got_frame;

	AVStream *out_stream;
	AVStream *in_stream;
	AVCodecContext *dec_ctx, *enc_ctx;
	AVCodec *encoder;

	fp_open = fopen("cuc60anniversary_start.ts", "rb");	//视频源文件
	fp_write=fopen("cuc60anniversary_start.h264","wb+"); //输出文件

	av_register_all();
	ifmt_ctx=avformat_alloc_context();
	avformat_alloc_output_context2(&ofmt_ctx, NULL, "h264", NULL);

	unsigned char* inbuffer=NULL;
	unsigned char* outbuffer=NULL;
	inbuffer=(unsigned char*)av_malloc(32768);
	outbuffer=(unsigned char*)av_malloc(32768);

	/*open input file*/
	AVIOContext *avio_in =avio_alloc_context(inbuffer, 32768,0,NULL,read_buffer,NULL,NULL);
	if(avio_in==NULL)
		goto end;
	ifmt_ctx->pb=avio_in;
	ifmt_ctx->flags=AVFMT_FLAG_CUSTOM_IO;
	if ((ret = avformat_open_input(&ifmt_ctx, "whatever", NULL, NULL)) < 0) {
		av_log(NULL, AV_LOG_ERROR, "Cannot open input file\n");
		return ret;
	}
	if ((ret = avformat_find_stream_info(ifmt_ctx, NULL)) < 0) {
		av_log(NULL, AV_LOG_ERROR, "Cannot find stream information\n");
		return ret;
	}
	for (i = 0; i < ifmt_ctx->nb_streams; i++) {
		AVStream *stream;
		AVCodecContext *codec_ctx;
		stream = ifmt_ctx->streams[i];
		codec_ctx = stream->codec;
		/* Reencode video & audio and remux subtitles etc. */
		if (codec_ctx->codec_type == AVMEDIA_TYPE_VIDEO){
			/* Open decoder */
			ret = avcodec_open2(codec_ctx,
				avcodec_find_decoder(codec_ctx->codec_id), NULL);
			if (ret < 0) {
				av_log(NULL, AV_LOG_ERROR, "Failed to open decoder for stream #%u\n", i);
				return ret;
			}
		}
	}
	//av_dump_format(ifmt_ctx, 0, "whatever", 0);

	/*open output file*/
	AVIOContext *avio_out =avio_alloc_context(outbuffer, 32768,1,NULL,NULL,write_buffer,NULL);
	if(avio_out==NULL)
		goto end;
	//avio_out->write_packet=write_packet;
	ofmt_ctx->pb=avio_out;
	ofmt_ctx->flags=AVFMT_FLAG_CUSTOM_IO;
	for (i = 0; i < 1; i++) {
		out_stream = avformat_new_stream(ofmt_ctx, NULL);
		if (!out_stream) {
			av_log(NULL, AV_LOG_ERROR, "Failed allocating output stream\n");
			return AVERROR_UNKNOWN;
		}
		in_stream = ifmt_ctx->streams[i];
		dec_ctx = in_stream->codec;
		enc_ctx = out_stream->codec;
		if (dec_ctx->codec_type == AVMEDIA_TYPE_VIDEO)
		{
			encoder = avcodec_find_encoder(AV_CODEC_ID_H264);
			enc_ctx->height = dec_ctx->height;
			enc_ctx->width = dec_ctx->width;
			enc_ctx->sample_aspect_ratio = dec_ctx->sample_aspect_ratio;
			enc_ctx->pix_fmt = encoder->pix_fmts[0];
			enc_ctx->time_base = dec_ctx->time_base;
			//enc_ctx->time_base.num = 1;
			//enc_ctx->time_base.den = 25;
			//H264的必备选项，没有就会错
			enc_ctx->me_range=16;
			enc_ctx->max_qdiff = 4;
			enc_ctx->qmin = 10;
			enc_ctx->qmax = 51;
			enc_ctx->qcompress = 0.6;
			enc_ctx->refs=3;
			enc_ctx->bit_rate = 500000;

			ret = avcodec_open2(enc_ctx, encoder, NULL);
			if (ret < 0) {
				av_log(NULL, AV_LOG_ERROR, "Cannot open video encoder for stream #%u\n", i);
				return ret;
			}
		}
		else if (dec_ctx->codec_type == AVMEDIA_TYPE_UNKNOWN) {
			av_log(NULL, AV_LOG_FATAL, "Elementary stream #%d is of unknown type, cannot proceed\n", i);
			return AVERROR_INVALIDDATA;
		} else {
			/* if this stream must be remuxed */
			ret = avcodec_copy_context(ofmt_ctx->streams[i]->codec,
				ifmt_ctx->streams[i]->codec);
			if (ret < 0) {
				av_log(NULL, AV_LOG_ERROR, "Copying stream context failed\n");
				return ret;
			}
		}
		if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
			enc_ctx->flags |= CODEC_FLAG_GLOBAL_HEADER;
	}
	//av_dump_format(ofmt_ctx, 0, "whatever", 1);
	/* init muxer, write output file header */
	ret = avformat_write_header(ofmt_ctx, NULL);
	if (ret < 0) {
		av_log(NULL, AV_LOG_ERROR, "Error occurred when opening output file\n");
		return ret;
	}

	i=0;
	/* read all packets */
	while (1) {
		i++;
		if ((ret = av_read_frame(ifmt_ctx, &packet)) < 0)
			break;
		stream_index = packet.stream_index;
		if(stream_index!=0)
			continue;
		type = ifmt_ctx->streams[packet.stream_index]->codec->codec_type;
		av_log(NULL, AV_LOG_DEBUG, "Demuxer gave frame of stream_index %u\n",
			stream_index);

		av_log(NULL, AV_LOG_DEBUG, "Going to reencode the frame\n");
		frame = av_frame_alloc();
		if (!frame) {
			ret = AVERROR(ENOMEM);
			break;
		}
		packet.dts = av_rescale_q_rnd(packet.dts,
			ifmt_ctx->streams[stream_index]->time_base,
			ifmt_ctx->streams[stream_index]->codec->time_base,
			(AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
		packet.pts = av_rescale_q_rnd(packet.pts,
			ifmt_ctx->streams[stream_index]->time_base,
			ifmt_ctx->streams[stream_index]->codec->time_base,
			(AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
		ret = avcodec_decode_video2(ifmt_ctx->streams[stream_index]->codec, frame,
			&got_frame, &packet);
		printf("Decode 1 Packet\tsize:%d\tpts:%d\n",packet.size,packet.pts);

		if (ret < 0) {
			av_frame_free(&frame);
			av_log(NULL, AV_LOG_ERROR, "Decoding failed\n");
			break;
		}
		if (got_frame) {
			frame->pts = av_frame_get_best_effort_timestamp(frame);
			frame->pict_type=AV_PICTURE_TYPE_NONE;

			enc_pkt.data = NULL;
			enc_pkt.size = 0;
			av_init_packet(&enc_pkt);
			ret = avcodec_encode_video2 (ofmt_ctx->streams[stream_index]->codec, &enc_pkt,
				frame, &enc_got_frame);

			printf("Encode 1 Packet\tsize:%d\tpts:%d\n",enc_pkt.size,enc_pkt.pts);

			av_frame_free(&frame);
			if (ret < 0)
				goto end;
			if (!enc_got_frame)
				continue;
			/* prepare packet for muxing */
			enc_pkt.stream_index = stream_index;
			enc_pkt.dts = av_rescale_q_rnd(enc_pkt.dts,
				ofmt_ctx->streams[stream_index]->codec->time_base,
				ofmt_ctx->streams[stream_index]->time_base,
				(AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
			enc_pkt.pts = av_rescale_q_rnd(enc_pkt.pts,
				ofmt_ctx->streams[stream_index]->codec->time_base,
				ofmt_ctx->streams[stream_index]->time_base,
				(AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
			enc_pkt.duration = av_rescale_q(enc_pkt.duration,
				ofmt_ctx->streams[stream_index]->codec->time_base,
				ofmt_ctx->streams[stream_index]->time_base);
			av_log(NULL, AV_LOG_INFO, "Muxing frame %d\n",i);
			/* mux encoded frame */
			av_write_frame(ofmt_ctx,&enc_pkt);
			if (ret < 0)
				goto end;
		} else {
			av_frame_free(&frame);
		}

		av_free_packet(&packet);
	}

	/* flush encoders */
	for (i = 0; i < 1; i++) {
		/* flush encoder */
		ret = flush_encoder(ofmt_ctx,i);
		if (ret < 0) {
			av_log(NULL, AV_LOG_ERROR, "Flushing encoder failed\n");
			goto end;
		}
	}
	av_write_trailer(ofmt_ctx);
end:
	av_freep(avio_in);
	av_freep(avio_out);
	av_free(inbuffer);
	av_free(outbuffer);
	av_free_packet(&packet);
	av_frame_free(&frame);
	avformat_close_input(&ifmt_ctx);
	avformat_free_context(ofmt_ctx);

	fcloseall();

	if (ret < 0)
		av_log(NULL, AV_LOG_ERROR, "Error occurred\n");
	return (ret? 1:0);
}

结果

程序运行的结果如下图所示。

转码前的视频信息使用MediaInfo查看如下图所示。

转码后的视频信息使用MediaInfo查看如下图所示。

下载

simplest ffmpeg mem handler

项目主页

SourceForge：https://sourceforge.net/projects/simplestffmpegmemhandler/

Github：https://github.com/leixiaohua1020/simplest_ffmpeg_mem_handler

开源中国：http://git.oschina.net/leixiaohua1020/simplest_ffmpeg_mem_handler

CSDN下载地址：
http://download.csdn.net/detail/leixiaohua1020/8003731

 本工程包含两个FFmpeg读写内存的例子：
 simplest_ffmpeg_mem_player：基于FFmpeg的内存播放器。
 simplest_ffmpeg_mem_transcoder：基于FFmpeg的内存转码器。
 

更新-1.1 (2015.2.13)=========================================

这次考虑到了跨平台的要求，调整了源代码。经过这次调整之后，源代码可以在以下平台编译通过：

VC++：打开sln文件即可编译，无需配置。

cl.exe：打开compile_cl.bat即可命令行下使用cl.exe进行编译，注意可能需要按照VC的安装路径调整脚本里面的参数。编译命令如下。

::VS2010 Environment
call "D:\Program Files\Microsoft Visual Studio 10.0\VC\vcvarsall.bat"
::include
@set INCLUDE=include;%INCLUDE%
::lib
@set LIB=lib;%LIB%
::compile and link
cl simplest_ffmpeg_mem_transcoder.cpp /link avcodec.lib avformat.lib avutil.lib ^
avdevice.lib avfilter.lib postproc.lib swresample.lib swscale.lib /OPT:NOREF

MinGW：MinGW命令行下运行compile_mingw.sh即可使用MinGW的g++进行编译。编译命令如下。

g++ simplest_ffmpeg_mem_transcoder.cpp -g -o simplest_ffmpeg_mem_transcoder.exe \
-I /usr/local/include -L /usr/local/lib \
-lavcodec -lavformat -lavutil -lavdevice -lavfilter -lpostproc -lswresample -lswscale

GCC：Linux或者MacOS命令行下运行compile_gcc.sh即可使用GCC进行编译。编译命令如下。

gcc simplest_ffmpeg_mem_transcoder.cpp -g -o simplest_ffmpeg_mem_transcoder.out \
-I /usr/local/include -L /usr/local/lib \
-lavcodec -lavformat -lavutil -lavdevice -lavfilter -lpostproc -lswresample -lswscale

PS：相关的编译命令已经保存到了工程文件夹中

CSDN下载地址：http://download.csdn.net/detail/leixiaohua1020/8445795

SourceForge上已经更新。