最简单的基于FFmpeg的内存读写的例子：内存转码器

http://blog.csdn.net/leixiaohua1020/article/details/39759623

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目录(?)[+]

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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

=====================================================

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：

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/**

* 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。

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::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。

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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。

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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。



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