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基于最简单的FFmpeg样品系列读写内存列表：
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上篇文章记录了一个基于FFmpeg的内存播放器，能够使用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。
该转码器能够使用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。
关于怎样从内存读取数据，以及怎样将数据输出到内存，能够參考文章：
FFmpeg读写内存的关键点有2个：
1. 初始化自己定义的AVIOContext，指定自己定义的回调函数。
2. 自己写回调函数。
注意函数的參数和返回值（尤其是返回值）。
转码实际上就是解码和编码的结合。
该方面的知识能够參考文章：
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）
流程
程序的流程图例如以下图所看到的。从图中能够看出，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。
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代码
以下直接贴上代码：
/**
* 最简单的基于FFmpeg的内存读写样例（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
*
* 本程序实现了随意格式视频数据（比如MPEG2）转码为H.264码流数据。
* 本程序并非对文件进行处理，而是对内存中的视频数据进行处理。
* 它从内存读取数据，而且将转码后的数据输出到内存中。
* 是最简单的使用FFmpeg读写内存的样例。
*
* 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, 32768,0,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
程序执行的结果例如以下图所看到的。
转码前的视频信息使用MediaInfo查看例如以下图所看到的。
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转码后的视频信息使用MediaInfo查看例如以下图所看到的。
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
本工程包括两个FFmpeg读写内存的样例：
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，调整了源码。经过这次调整之后，源码能够在以下平台编译通过：
VC++：打开sln文件就可以编译，无需配置。
cl.exe：打开compile_cl.bat就可以命令行下使用cl.exe进行编译。注意可能须要依照VC的安装路径调整脚本里面的參数。编译命令例如以下。
::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命令行下执行compile_mingw.sh就可以使用MinGW的g++进行编译。编译命令例如以下。
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命令行下执行compile_gcc.sh就可以使用GCC进行编译。
编译命令例如以下。
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目录中
CSDN下载：http://download.csdn.net/detail/leixiaohua1020/8445795
SourceForge已经更新。