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本文介绍一个最简单的基于FFMPEG的视频编码器。该编码器实现了YUV420P的像素数据编码为H.264的压缩编码数据。编码器代码十分简单,但是每一行代码都很重要,适合好好研究一下。弄清楚了本代码也就基本弄清楚了FFMPEG的编码流程。
下面附一张使用FFmpeg编码视频的流程图。使用该流程,不仅可以编码H.264的视频,而且可以编码MPEG4/MPEG2/VP8等等各种FFmpeg支持的视频。图中蓝色背景的函数是实际输出数据的函数。浅绿色的函数是视频编码的函数。
简单介绍一下流程中各个函数的意义:
av_register_all():注册FFmpeg所有编解码器。
avformat_alloc_output_context2():初始化输出码流的AVFormatContext。
avio_open():打开输出文件。
av_new_stream():创建输出码流的AVStream。
avcodec_find_encoder():查找编码器。
avcodec_open2():打开编码器。
avformat_write_header():写文件头(对于某些没有文件头的封装格式,不需要此函数。比如说MPEG2TS)。
avcodec_encode_video2():编码一帧视频。即将AVFrame(存储YUV像素数据)编码为AVPacket(存储H.264等格式的码流数据)。
av_write_frame():将编码后的视频码流写入文件。
flush_encoder():输入的像素数据读取完成后调用此函数。用于输出编码器中剩余的AVPacket。
av_write_trailer():写文件尾(对于某些没有文件头的封装格式,不需要此函数。比如说MPEG2TS)。
- * 本程序实现了YUV像素数据编码为视频码流(H264,MPEG2,VP8等等)。
- * 是最简单的FFmpeg视频编码方面的教程。
- * 通过学习本例子可以了解FFmpeg的编码流程。
- * This software encode YUV420P data to H.264 bitstream.
- * It's the simplest video encoding software based on FFmpeg.
- * Suitable for beginner of FFmpeg
- */
- #include <stdio.h>
- #define __STDC_CONSTANT_MACROS
- #ifdef _WIN32
- //Windows
- extern "C"
- {
- #include "libavutil/opt.h"
- #include "libavcodec/avcodec.h"
- #include "libavformat/avformat.h"
- };
- #else
- //Linux...
- #ifdef __cplusplus
- extern "C"
- {
- #endif
- #include <libavutil/opt.h>
- #include <libavcodec/avcodec.h>
- #include <libavformat/avformat.h>
- #ifdef __cplusplus
- };
- #endif
- #endif
- 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) {
- 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;
- }
- printf("Flush Encoder: Succeed to encode 1 frame!\tsize:%5d\n",enc_pkt.size);
- /* mux encoded frame */
- ret = av_write_frame(fmt_ctx, &enc_pkt);
- if (ret < 0)
- break;
- }
- return ret;
- }
- int main(int argc, char* argv[])
- {
- AVFormatContext* pFormatCtx;
- AVOutputFormat* fmt;
- AVStream* video_st;
- AVCodecContext* pCodecCtx;
- AVCodec* pCodec;
- AVPacket pkt;
- uint8_t* picture_buf;
- AVFrame* pFrame;
- int picture_size;
- int y_size;
- int framecnt=0;
- //FILE *in_file = fopen("src01_480x272.yuv", "rb"); //Input raw YUV data
- FILE *in_file = fopen("../ds_480x272.yuv", "rb"); //Input raw YUV data
- int in_w=480,in_h=272; //Input data's width and height
- int framenum=100; //Frames to encode
- //const char* out_file = "src01.h264"; //Output Filepath
- //const char* out_file = "src01.ts";
- //const char* out_file = "src01.hevc";
- const char* out_file = "ds.h264";
- av_register_all();
- //Method1.
- pFormatCtx = avformat_alloc_context();
- //Guess Format
- fmt = av_guess_format(NULL, out_file, NULL);
- pFormatCtx->oformat = fmt;
- //Method 2.
- //avformat_alloc_output_context2(&pFormatCtx, NULL, NULL, out_file);
- //fmt = pFormatCtx->oformat;
- //Open output URL
- if (avio_open(&pFormatCtx->pb,out_file, AVIO_FLAG_READ_WRITE) < 0){
- printf("Failed to open output file! \n");
- return -1;
- }
- video_st = avformat_new_stream(pFormatCtx, 0);
- //video_st->time_base.num = 1;
- //video_st->time_base.den = 25;
- if (video_st==NULL){
- return -1;
- }
- //Param that must set
- pCodecCtx = video_st->codec;
- //pCodecCtx->codec_id =AV_CODEC_ID_HEVC;
- pCodecCtx->codec_id = fmt->video_codec;
- pCodecCtx->codec_type = AVMEDIA_TYPE_VIDEO;
- pCodecCtx->pix_fmt = AV_PIX_FMT_YUV420P;
- pCodecCtx->width = in_w;
- pCodecCtx->height = in_h;
- pCodecCtx->bit_rate = 400000;
- pCodecCtx->gop_size=250;
- pCodecCtx->time_base.num = 1;
- pCodecCtx->time_base.den = 25;
- //H264
- //pCodecCtx->me_range = 16;
- //pCodecCtx->max_qdiff = 4;
- //pCodecCtx->qcompress = 0.6;
- pCodecCtx->qmin = 10;
- pCodecCtx->qmax = 51;
- //Optional Param
- pCodecCtx->max_b_frames=3;
- // Set Option
- AVDictionary *param = 0;
- //H.264
- if(pCodecCtx->codec_id == AV_CODEC_ID_H264) {
- av_dict_set(¶m, "preset", "slow", 0);
- av_dict_set(¶m, "tune", "zerolatency", 0);
- //av_dict_set(¶m, "profile", "main", 0);
- }
- //H.265
- if(pCodecCtx->codec_id == AV_CODEC_ID_H265){
- av_dict_set(¶m, "preset", "ultrafast", 0);
- av_dict_set(¶m, "tune", "zero-latency", 0);
- }
- //Show some Information
- av_dump_format(pFormatCtx, 0, out_file, 1);
- pCodec = avcodec_find_encoder(pCodecCtx->codec_id);
- if (!pCodec){
- printf("Can not find encoder! \n");
- return -1;
- }
- if (avcodec_open2(pCodecCtx, pCodec,¶m) < 0){
- printf("Failed to open encoder! \n");
- return -1;
- }
- pFrame = av_frame_alloc();
- picture_size = avpicture_get_size(pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height);
- picture_buf = (uint8_t *)av_malloc(picture_size);
- avpicture_fill((AVPicture *)pFrame, picture_buf, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height);
- //Write File Header
- avformat_write_header(pFormatCtx,NULL);
- av_new_packet(&pkt,picture_size);
- y_size = pCodecCtx->width * pCodecCtx->height;
- for (int i=0; i<framenum; i++){
- //Read raw YUV data
- if (fread(picture_buf, 1, y_size*3/2, in_file) <= 0){
- printf("Failed to read raw data! \n");
- return -1;
- }else if(feof(in_file)){
- break;
- }
- pFrame->data[0] = picture_buf; // Y
- pFrame->data[1] = picture_buf+ y_size; // U
- pFrame->data[2] = picture_buf+ y_size*5/4; // V
- //PTS
- //pFrame->pts=i;
- pFrame->pts=i*(video_st->time_base.den)/((video_st->time_base.num)*25);
- int got_picture=0;
- //Encode
- int ret = avcodec_encode_video2(pCodecCtx, &pkt,pFrame, &got_picture);
- if(ret < 0){
- printf("Failed to encode! \n");
- return -1;
- }
- if (got_picture==1){
- printf("Succeed to encode frame: %5d\tsize:%5d\n",framecnt,pkt.size);
- framecnt++;
- pkt.stream_index = video_st->index;
- ret = av_write_frame(pFormatCtx, &pkt);
- av_free_packet(&pkt);
- }
- }
- //Flush Encoder
- int ret = flush_encoder(pFormatCtx,0);
- if (ret < 0) {
- printf("Flushing encoder failed\n");
- return -1;
- }
- //Write file trailer
- av_write_trailer(pFormatCtx);
- //Clean
- if (video_st){
- avcodec_close(video_st->codec);
- av_free(pFrame);
- av_free(picture_buf);
- }
- avio_close(pFormatCtx->pb);
- avformat_free_context(pFormatCtx);
- fclose(in_file);
- return 0;
- }