在 mp4 容器中保存视频时 FPS 太高

Posted 2023-03-13

【中文标题】在 mp4 容器中保存视频时 FPS 太高

【英文标题】：FPS too high when saving video in mp4 container

【发布时间】：2012-11-13 22:37:04

【问题描述】：

当我从 avi 文件解码帧，然后在 x264 中解码它们并保存到 mp4 文件时，输出文件的 fps 始终为 12,800。因此文件播放速度非常快。但是，当我以 avi 格式而不是 mp4 保存编码为 h264 帧时，fps 就是我想要的 - 25。

可能是什么问题？

这里是我在VS2010中写的代码：

#include "stdafx.h"
#include "inttypes.h"

extern "C" 
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libavutil/avutil.h"
#include <libswscale/swscale.h>
#include <libavutil/opt.h>
#include <libswscale/swscale.h>
#include <libavutil/imgutils.h>


#include <iostream>
using namespace std;

int main(int argc, char* argv[])

   const char* inFileName = "C:\\000227_C1_GAME.avi";
   const char* outFileName = "c:\\test.avi";
   const char* outFileType = "avi";

   av_register_all();

   AVFormatContext* inContainer = NULL;   
   if(avformat_open_input(&inContainer, inFileName, NULL, NULL) < 0)   
      exit(1);

   if(avformat_find_stream_info(inContainer, NULL) < 0)
      exit(1);

   // Find video stream
   int videoStreamIndex = -1;
   for (unsigned int i = 0; i < inContainer->nb_streams; ++i)
   
      if (inContainer->streams[i] && inContainer->streams[i]->codec &&
         inContainer->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
      
         videoStreamIndex = i;
         break;
      
   
   if (videoStreamIndex == -1) exit(1);

   AVFormatContext* outContainer = NULL;
   if(avformat_alloc_output_context2(&outContainer, NULL, outFileType, outFileName) < 0)
      exit(1);

   // ---------------------------- 
   // Decoder
   // ---------------------------- 
   AVStream const *const inStream = inContainer->streams[videoStreamIndex];
   AVCodec *const decoder = avcodec_find_decoder(inStream->codec->codec_id);
   if(!decoder) 
      exit(1);
   if(avcodec_open2(inStream->codec, decoder, NULL) < 0) 
      exit(1);

   // ---------------------------- 
   // Encoder
   // ----------------------------             
   AVCodec *encoder = avcodec_find_encoder(AV_CODEC_ID_H264);
   if(!encoder) 
      exit(1);
   AVStream *outStream = avformat_new_stream(outContainer, encoder);      
   if(!outStream)
      exit(1);
   avcodec_get_context_defaults3(outStream->codec, encoder);   

   // Construct encoder
   if(outContainer->oformat->flags & AVFMT_GLOBALHEADER) 
      outStream->codec->flags |= CODEC_FLAG_GLOBAL_HEADER;   

   outStream->codec->coder_type = AVMEDIA_TYPE_VIDEO;
   outStream->codec->pix_fmt = AV_PIX_FMT_YUV420P;
   outStream->codec->width = inStream->codec->width;
   outStream->codec->height = inStream->codec->height;
   outStream->codec->codec_id = encoder->id;
   outStream->codec->bit_rate = 500000;
   //outStream->codec->rc_min_rate = 600000;
   //outStream->codec->rc_max_rate = 800000;

   outStream->codec->time_base.den = 25;
   outStream->codec->time_base.num = 1;
   outStream->codec->gop_size = 250; // Keyframe interval(=GOP length). Determines maximum distance distance between I-frames
   outStream->codec->keyint_min = 25; // minimum GOP size
   outStream->codec->max_b_frames = 3;//16; // maximum number of B-frames between non-B-frames
   outStream->codec->b_frame_strategy = 1; // decides the best number of B-frames to use. Default mode in x264.
   outStream->codec->scenechange_threshold = 40;
   outStream->codec->refs = 6; // abillity to reference frames other than the one immediately prior to the current frame. specify how many references can be used.
   outStream->codec->qmin = 0;//10;
   outStream->codec->qmax = 69;//51;
   outStream->codec->qcompress = 0.6;
   outStream->codec->max_qdiff = 4;
   outStream->codec->i_quant_factor = 1.4;//0.71;   

   outStream->codec->refs=1;//3;
   outStream->codec->chromaoffset = -2;
   outStream->codec->thread_count = 1;   
   outStream->codec->trellis = 1;
   outStream->codec->me_range = 16;
   outStream->codec->me_method = ME_HEX; //hex
   outStream->codec->flags2 |= CODEC_FLAG2_FAST;   
   outStream->codec->coder_type = 1;


   if(outStream->codec->codec_id == AV_CODEC_ID_H264)
   
        av_opt_set(outStream->codec->priv_data, "preset", "slow", 0);
   

   // Open encoder
   if(avcodec_open2(outStream->codec, encoder, NULL) < 0) 
      exit(1);

   // Open output container
   if(avio_open(&outContainer->pb, outFileName, AVIO_FLAG_WRITE) < 0)
      exit(1);

   //close_o

   AVFrame *decodedFrame = avcodec_alloc_frame();
   if(!decodedFrame) 
      exit(1);
   AVFrame *encodeFrame = avcodec_alloc_frame();
   if(!encodeFrame) 
      exit(1);
   encodeFrame->format = outStream->codec->pix_fmt;
   encodeFrame->width = outStream->codec->width;
   encodeFrame->height = outStream->codec->height;
   if(av_image_alloc(encodeFrame->data, encodeFrame->linesize, 
                 outStream->codec->width, outStream->codec->height, 
                 outStream->codec->pix_fmt, 1) < 0)
      exit(1);

   av_dump_format(inContainer, 0, inFileName,0);

   //Write header to ouput container
   avformat_write_header(outContainer, NULL);

   AVPacket decodePacket, encodedPacket;
   int got_frame, len;
   while(av_read_frame(inContainer, &decodePacket)>=0)
         
      if (decodePacket.stream_index == videoStreamIndex)
                        
         len = avcodec_decode_video2(inStream->codec, decodedFrame, &got_frame, &decodePacket);
         if(len < 0)
            exit(1);
         if(got_frame)
         
            av_init_packet(&encodedPacket);
            encodedPacket.data = NULL;
            encodedPacket.size = 0;         
            if(avcodec_encode_video2(outStream->codec, &encodedPacket, decodedFrame, &got_frame) < 0)
               exit(1);
            if(got_frame)
            
               if (outStream->codec->coded_frame->key_frame)
                  encodedPacket.flags |= AV_PKT_FLAG_KEY;

               encodedPacket.stream_index = outStream->index;

               if(av_interleaved_write_frame(outContainer, &encodedPacket) < 0)
                  exit(1);

               av_free_packet(&encodedPacket);
            
         
      

      av_free_packet(&decodePacket);
   
   av_write_trailer(outContainer);
   avio_close(outContainer->pb);

   avcodec_free_frame(&encodeFrame);
   avcodec_free_frame(&decodedFrame);

   avformat_free_context(outContainer);
   av_close_input_file(inContainer);
   return 0;

【问题讨论】：

有人可以帮我吗？

【参考方案1】：

问题出在数据包的 PTS 和 DTS 上。在将数据包写入输出之前（av_interleaved_write_frame 命令之前）像这样设置 PTS 和 DTS

if (encodedPacket.pts != AV_NOPTS_VALUE)
    encodedPacket.pts =  av_rescale_q(encodedPacket.pts, outStream->codec->time_base, outStream->time_base);
if (encodedPacket.dts != AV_NOPTS_VALUE)
    encodedPacket.dts = av_rescale_q(encodedPacket.dts, outStream->codec->time_base, outStream->time_base);

【讨论】：

确保设置outStream->codec->time_base.num = 1; outStream->codec->time_base.den = fps;

似乎AVStream.codec 现已弃用。