=====================================================
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：
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- #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;
-
-
- 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;
- }
- }
-
-
- 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);
-
- 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;}
-
- 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");
-
- 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");
- fp_write=fopen("cuc60anniversary_start.h264","wb+");
-
- 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);
-
-
- 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;
-
- if (codec_ctx->codec_type == AVMEDIA_TYPE_VIDEO){
-
- 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;
- }
- }
- }
-
-
-
- AVIOContext *avio_out =avio_alloc_context(outbuffer, 32768,1,NULL,NULL,write_buffer,NULL);
- if(avio_out==NULL)
- goto end;
-
- 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->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 {
-
- 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;
- }
-
-
- 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;
-
- 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;
-
- 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);
-
- av_write_frame(ofmt_ctx,&enc_pkt);
- if (ret < 0)
- goto end;
- } else {
- av_frame_free(&frame);
- }
-
- av_free_packet(&packet);
- }
-
-
- for (i = 0; i < 1; i++) {
-
- 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。
