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15 octobre 2019, par Matomo Core Team — Community -
ffmpeg record video plays too fast
29 avril 2023, par Kris XiaI'm a college student and I am studying FFmpeg now.



I have wrote a software that can record desktops and audio('virtual-audio-capturer') with FFmpeg.And I am now writing Audio and Video Synchronization.
I met some problems that video recording plays too fast.



When I look for audio and video synchronization help on the Internet,I find a formula for calculating PTS :



pts = n * ((1 / timbase)/ fps)



When I use this formula,I find a phenomenon.



1.The higher frame rate is,the faster the video playback speed.



2.The slower the frame rate, the faster the video playback.



Also I find while the framerate is 10,the video playback speed will be right.



Why has this situation happened ?



I have thought this question for three days. I really hope someone can help me solve this problem.



I really appreciate the help.



#include "stdafx.h"

#ifdef __cplusplus
extern "C"
{
#endif
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswscale/swscale.h"
#include "libavdevice/avdevice.h"
#include "libavutil/audio_fifo.h"

#include "libavfilter/buffersink.h"
#include "libavfilter/buffersrc.h"
#include "libavutil/imgutils.h"
#include "libavutil/mathematics.h"
#include "libavutil/samplefmt.h"
#include "libavutil/time.h"
#include "libavutil/opt.h"
#include "libavutil/pixdesc.h"
#include "libavutil/file.h"
#include "libavutil/mem.h"
#include "libavutil/frame.h"
#include "libavfilter/avfilter.h"
#include "libswresample/swresample.h"

#pragma comment(lib, "avcodec.lib")
#pragma comment(lib, "avformat.lib")
#pragma comment(lib, "avutil.lib")
#pragma comment(lib, "avdevice.lib")
#pragma comment(lib, "avfilter.lib")

#pragma comment(lib, "avfilter.lib")
#pragma comment(lib, "postproc.lib")
#pragma comment(lib, "swresample.lib")
#pragma comment(lib, "swscale.lib")
#ifdef __cplusplus
};
#endif

AVFormatContext *pFormatCtx_Video = NULL, *pFormatCtx_Audio = NULL, *pFormatCtx_Out = NULL;

AVCodecContext *outVideoCodecCtx = NULL;
AVCodecContext *outAudioCodecCtx = NULL;

AVStream *pVideoStream = NULL, *pAudioStream = NULL;

AVCodec *outAVCodec;
AVCodec *outAudioCodec;

AVCodecContext *pCodecCtx_Video;
AVCodec *pCodec_Video;
AVFifoBuffer *fifo_video = NULL;
AVAudioFifo *fifo_audio = NULL;
int VideoIndex, AudioIndex;
int codec_id;

CRITICAL_SECTION AudioSection, VideoSection;



SwsContext *img_convert_ctx;
int frame_size = 0;

uint8_t *picture_buf = NULL, *frame_buf = NULL;

bool bCap = true;

DWORD WINAPI ScreenCapThreadProc( LPVOID lpParam );
DWORD WINAPI AudioCapThreadProc( LPVOID lpParam );

int OpenVideoCapture()
{
 AVInputFormat *ifmt=av_find_input_format("gdigrab");
 AVDictionary *options = NULL;
 av_dict_set(&options, "framerate", "60", NULL);
 if(avformat_open_input(&pFormatCtx_Video, "desktop", ifmt, &options)!=0)
 {
 printf("Couldn't open input stream.(无法打开视频输入流)\n");
 return -1;
 }
 if(avformat_find_stream_info(pFormatCtx_Video,NULL)<0)
 {
 printf("Couldn't find stream information.(无法获取视频流信息)\n");
 return -1;
 }
 if (pFormatCtx_Video->streams[0]->codec->codec_type != AVMEDIA_TYPE_VIDEO)
 {
 printf("Couldn't find video stream information.(无法获取视频流信息)\n");
 return -1;
 }
 pCodecCtx_Video = pFormatCtx_Video->streams[0]->codec;
 pCodec_Video = avcodec_find_decoder(pCodecCtx_Video->codec_id);
 if(pCodec_Video == NULL)
 {
 printf("Codec not found.(没有找到解码器)\n");
 return -1;
 }
 if(avcodec_open2(pCodecCtx_Video, pCodec_Video, NULL) < 0)
 {
 printf("Could not open codec.(无法打开解码器)\n");
 return -1;
 }

 av_dump_format(pFormatCtx_Video, 0, NULL, 0);

 img_convert_ctx = sws_getContext(pCodecCtx_Video->width, pCodecCtx_Video->height, pCodecCtx_Video->pix_fmt, 
 pCodecCtx_Video->width, pCodecCtx_Video->height, PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL); 

 frame_size = avpicture_get_size(pCodecCtx_Video->pix_fmt, pCodecCtx_Video->width, pCodecCtx_Video->height);
 fifo_video = av_fifo_alloc(30 * avpicture_get_size(AV_PIX_FMT_YUV420P, pCodecCtx_Video->width, pCodecCtx_Video->height));

 return 0;
}

static char *dup_wchar_to_utf8(wchar_t *w)
{
 char *s = NULL;
 int l = WideCharToMultiByte(CP_UTF8, 0, w, -1, 0, 0, 0, 0);
 s = (char *) av_malloc(l);
 if (s)
 WideCharToMultiByte(CP_UTF8, 0, w, -1, s, l, 0, 0);
 return s;
}

int OpenAudioCapture()
{
 AVInputFormat *pAudioInputFmt = av_find_input_format("dshow");
 char * psDevName = dup_wchar_to_utf8(L"audio=virtual-audio-capturer");

 if (avformat_open_input(&pFormatCtx_Audio, psDevName, pAudioInputFmt,NULL) < 0)
 {
 printf("Couldn't open input stream.(无法打开音频输入流)\n");
 return -1;
 }

 if(avformat_find_stream_info(pFormatCtx_Audio,NULL)<0) 
 return -1; 

 if(pFormatCtx_Audio->streams[0]->codec->codec_type != AVMEDIA_TYPE_AUDIO)
 {
 printf("Couldn't find video stream information.(无法获取音频流信息)\n");
 return -1;
 }

 AVCodec *tmpCodec = avcodec_find_decoder(pFormatCtx_Audio->streams[0]->codec->codec_id);
 if(0 > avcodec_open2(pFormatCtx_Audio->streams[0]->codec, tmpCodec, NULL))
 {
 printf("can not find or open audio decoder!\n");
 }

 av_dump_format(pFormatCtx_Audio, 0, NULL, 0);

 return 0;
}

int OpenOutPut()
{
 AVStream *pVideoStream = NULL, *pAudioStream = NULL;
 const char *outFileName = "test.mp4";
 avformat_alloc_output_context2(&pFormatCtx_Out, NULL, NULL, outFileName);

 if (pFormatCtx_Video->streams[0]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
 {
 VideoIndex = 0;
 pVideoStream = avformat_new_stream(pFormatCtx_Out, NULL);
 if (!pVideoStream)
 {
 printf("can not new stream for output!\n");
 return -1;
 }

 outVideoCodecCtx = avcodec_alloc_context3(outAVCodec);
 if ( !outVideoCodecCtx )
 {
 printf("Error : avcodec_alloc_context3()\n");
 return -1;
 }

 //set codec context param
 outVideoCodecCtx = pVideoStream->codec;
 outVideoCodecCtx->codec_id = AV_CODEC_ID_MPEG4;
 outVideoCodecCtx->width = pFormatCtx_Video->streams[0]->codec->width;
 outVideoCodecCtx->height = pFormatCtx_Video->streams[0]->codec->height;
 outVideoCodecCtx->time_base = pFormatCtx_Video->streams[0]->codec->time_base;
 outVideoCodecCtx->pix_fmt = AV_PIX_FMT_YUV420P;
 outVideoCodecCtx->codec_type = AVMEDIA_TYPE_VIDEO;

 if (codec_id == AV_CODEC_ID_H264)
 {
 av_opt_set(outVideoCodecCtx->priv_data, "preset", "slow", 0);
 }

 outAVCodec = avcodec_find_encoder(AV_CODEC_ID_MPEG4);
 if( !outAVCodec )
 {
 printf("\n\nError : avcodec_find_encoder()");
 return -1;
 }
 if (pFormatCtx_Out->oformat->flags & AVFMT_GLOBALHEADER)
 outVideoCodecCtx->flags |=CODEC_FLAG_GLOBAL_HEADER;

 if ((avcodec_open2(outVideoCodecCtx,outAVCodec, NULL)) < 0)
 {
 printf("can not open the encoder\n");
 return -1;
 }
 }

 if(pFormatCtx_Audio->streams[0]->codec->codec_type == AVMEDIA_TYPE_AUDIO)
 {
 AVCodecContext *pOutputCodecCtx;
 AudioIndex = 1;
 pAudioStream = avformat_new_stream(pFormatCtx_Out, NULL);

 pAudioStream->codec->codec = avcodec_find_encoder(pFormatCtx_Out->oformat->audio_codec);

 pOutputCodecCtx = pAudioStream->codec;

 pOutputCodecCtx->sample_rate = pFormatCtx_Audio->streams[0]->codec->sample_rate;
 pOutputCodecCtx->channel_layout = pFormatCtx_Out->streams[0]->codec->channel_layout;
 pOutputCodecCtx->channels = av_get_channel_layout_nb_channels(pAudioStream->codec->channel_layout);
 if(pOutputCodecCtx->channel_layout == 0)
 {
 pOutputCodecCtx->channel_layout = AV_CH_LAYOUT_STEREO;
 pOutputCodecCtx->channels = av_get_channel_layout_nb_channels(pOutputCodecCtx->channel_layout);

 }
 pOutputCodecCtx->sample_fmt = pAudioStream->codec->codec->sample_fmts[0];
 AVRational time_base={1, pAudioStream->codec->sample_rate};
 pAudioStream->time_base = time_base;
 //audioCodecCtx->time_base = time_base;

 pOutputCodecCtx->codec_tag = 0; 
 if (pFormatCtx_Out->oformat->flags & AVFMT_GLOBALHEADER) 
 pOutputCodecCtx->flags |= CODEC_FLAG_GLOBAL_HEADER;

 if (avcodec_open2(pOutputCodecCtx, pOutputCodecCtx->codec, 0) < 0)
 {
 printf("编码器打开失败,退出程序\n");
 return -1;
 }
 }

 if (!(pFormatCtx_Out->oformat->flags & AVFMT_NOFILE))
 {
 if(avio_open(&pFormatCtx_Out->pb, outFileName, AVIO_FLAG_WRITE) < 0)
 {
 printf("can not open output file handle!\n");
 return -1;
 }
 }

 if(avformat_write_header(pFormatCtx_Out, NULL) < 0)
 {
 printf("can not write the header of the output file!\n");
 return -1;
 }

 return 0;
}

int _tmain(int argc, _TCHAR* argv[])
{
 av_register_all();
 avdevice_register_all();
 if (OpenVideoCapture() < 0)
 {
 return -1;
 }
 if (OpenAudioCapture() < 0)
 {
 return -1;
 }
 if (OpenOutPut() < 0)
 {
 return -1;
 }
// int fps;
 /*printf("输入帧率:");
 scanf_s("%d",&fps);
 if ( NULL == fps)
 {
 fps = 10;
 }*/

 InitializeCriticalSection(&VideoSection);
 InitializeCriticalSection(&AudioSection);

 AVFrame *picture = av_frame_alloc();
 int size = avpicture_get_size(pFormatCtx_Out->streams[VideoIndex]->codec->pix_fmt, 
 pFormatCtx_Out->streams[VideoIndex]->codec->width, pFormatCtx_Out->streams[VideoIndex]->codec->height);
 picture_buf = new uint8_t[size];

 avpicture_fill((AVPicture *)picture, picture_buf, 
 pFormatCtx_Out->streams[VideoIndex]->codec->pix_fmt, 
 pFormatCtx_Out->streams[VideoIndex]->codec->width, 
 pFormatCtx_Out->streams[VideoIndex]->codec->height);



 //star cap screen thread
 CreateThread( NULL, 0, ScreenCapThreadProc, 0, 0, NULL);
 //star cap audio thread
 CreateThread( NULL, 0, AudioCapThreadProc, 0, 0, NULL);
 int64_t cur_pts_v=0,cur_pts_a=0;
 int VideoFrameIndex = 0, AudioFrameIndex = 0;

 while(1)
 {
 if (_kbhit() != 0 && bCap)
 {
 bCap = false;
 Sleep(2000);
 }
 if (fifo_audio && fifo_video)
 {
 int sizeAudio = av_audio_fifo_size(fifo_audio);
 int sizeVideo = av_fifo_size(fifo_video);
 //缓存数据写完就结束循环
 if (av_audio_fifo_size(fifo_audio) <= pFormatCtx_Out->streams[AudioIndex]->codec->frame_size && 
 av_fifo_size(fifo_video) <= frame_size && !bCap)
 {
 break;
 }
 }

 if(av_compare_ts(cur_pts_v, pFormatCtx_Out->streams[VideoIndex]->time_base, 
 cur_pts_a,pFormatCtx_Out->streams[AudioIndex]->time_base) <= 0)
 {
 if (av_fifo_size(fifo_video) < frame_size && !bCap)
 {
 cur_pts_v = 0x7fffffffffffffff;
 }
 if(av_fifo_size(fifo_video) >= size)
 {
 EnterCriticalSection(&VideoSection);
 av_fifo_generic_read(fifo_video, picture_buf, size, NULL); //将数据从avfifobuffer馈送到用户提供的回调。
 LeaveCriticalSection(&VideoSection);

 avpicture_fill((AVPicture *)picture, picture_buf,
 pFormatCtx_Out->streams[VideoIndex]->codec->pix_fmt,
 pFormatCtx_Out->streams[VideoIndex]->codec->width,
 pFormatCtx_Out->streams[VideoIndex]->codec->height); //根据指定的图像参数和提供的图像数据缓冲区设置图片字段。

 //pts = n * ((1 / timbase)/ fps);
 //picture->pts = VideoFrameIndex * ((pFormatCtx_Video->streams[0]->time_base.den / pFormatCtx_Video->streams[0]->time_base.num) / 24);
 picture->pts = VideoFrameIndex * ((outVideoCodecCtx->time_base.den * 100000 / outVideoCodecCtx->time_base.num) / 180);

 int got_picture = 0;
 AVPacket pkt;
 av_init_packet(&pkt);

 pkt.data = NULL;
 pkt.size = 0;
 //从帧中获取输入的原始视频数据
 int ret = avcodec_encode_video2(pFormatCtx_Out->streams[VideoIndex]->codec, &pkt, picture, &got_picture);
 if(ret < 0)
 {
 continue;
 }

 if (got_picture==1)
 {
 pkt.stream_index = VideoIndex;
 /*int count = 1;
 pkt.pts = pkt.dts = count * ((pFormatCtx_Video->streams[0]->time_base.den / pFormatCtx_Video->streams[0]->time_base.num) / 15);
 count++;*/

 //x = pts * (timebase1.num / timebase1.den )* (timebase2.den / timebase2.num);

 pkt.pts = av_rescale_q_rnd(pkt.pts, pFormatCtx_Video->streams[0]->time_base, 
 pFormatCtx_Out->streams[VideoIndex]->time_base, (AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX)); 
 pkt.dts = av_rescale_q_rnd(pkt.dts, pFormatCtx_Video->streams[0]->time_base, 
 pFormatCtx_Out->streams[VideoIndex]->time_base, (AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX)); 


 pkt.duration = ((pFormatCtx_Out->streams[0]->time_base.den / pFormatCtx_Out->streams[0]->time_base.num) / 60);
 //pkt.duration = 1000/60;
 //pkt.pts = pkt.dts = Count * (ofmt_ctx->streams[stream_index]->time_base.den) /ofmt_ctx->streams[stream_index]->time_base.num / 10;

 //Count++;


 cur_pts_v = pkt.pts;

 ret = av_interleaved_write_frame(pFormatCtx_Out, &pkt);
 //delete[] pkt.data;
 av_free_packet(&pkt);
 }
 VideoFrameIndex++;
 }
 }
 else
 {
 if (NULL == fifo_audio)
 {
 continue;//还未初始化fifo
 }
 if (av_audio_fifo_size(fifo_audio) < pFormatCtx_Out->streams[AudioIndex]->codec->frame_size && !bCap)
 {
 cur_pts_a = 0x7fffffffffffffff;
 }
 if(av_audio_fifo_size(fifo_audio) >= 
 (pFormatCtx_Out->streams[AudioIndex]->codec->frame_size > 0 ? pFormatCtx_Out->streams[AudioIndex]->codec->frame_size : 1024))
 {
 AVFrame *frame;
 frame = av_frame_alloc();
 frame->nb_samples = pFormatCtx_Out->streams[AudioIndex]->codec->frame_size>0 ? pFormatCtx_Out->streams[AudioIndex]->codec->frame_size: 1024;
 frame->channel_layout = pFormatCtx_Out->streams[AudioIndex]->codec->channel_layout;
 frame->format = pFormatCtx_Out->streams[AudioIndex]->codec->sample_fmt;
 frame->sample_rate = pFormatCtx_Out->streams[AudioIndex]->codec->sample_rate;
 av_frame_get_buffer(frame, 0);

 EnterCriticalSection(&AudioSection);
 av_audio_fifo_read(fifo_audio, (void **)frame->data, 
 (pFormatCtx_Out->streams[AudioIndex]->codec->frame_size > 0 ? pFormatCtx_Out->streams[AudioIndex]->codec->frame_size : 1024));
 LeaveCriticalSection(&AudioSection);

 AVPacket pkt_out;
 av_init_packet(&pkt_out);
 int got_picture = -1;
 pkt_out.data = NULL;
 pkt_out.size = 0;

 frame->pts = AudioFrameIndex * pFormatCtx_Out->streams[AudioIndex]->codec->frame_size;
 if (avcodec_encode_audio2(pFormatCtx_Out->streams[AudioIndex]->codec, &pkt_out, frame, &got_picture) < 0)
 {
 printf("can not decoder a frame");
 }
 av_frame_free(&frame);
 if (got_picture) 
 {
 pkt_out.stream_index = AudioIndex;
 pkt_out.pts = AudioFrameIndex * pFormatCtx_Out->streams[AudioIndex]->codec->frame_size;
 pkt_out.dts = AudioFrameIndex * pFormatCtx_Out->streams[AudioIndex]->codec->frame_size;
 pkt_out.duration = pFormatCtx_Out->streams[AudioIndex]->codec->frame_size;

 cur_pts_a = pkt_out.pts;

 int ret = av_interleaved_write_frame(pFormatCtx_Out, &pkt_out);
 av_free_packet(&pkt_out);
 }
 AudioFrameIndex++;
 }
 }
 }

 delete[] picture_buf;

 av_fifo_free(fifo_video);
 av_audio_fifo_free(fifo_audio);

 av_write_trailer(pFormatCtx_Out);

 avio_close(pFormatCtx_Out->pb);
 avformat_free_context(pFormatCtx_Out);

 if (pFormatCtx_Video != NULL)
 {
 avformat_close_input(&pFormatCtx_Video);
 pFormatCtx_Video = NULL;
 }
 if (pFormatCtx_Audio != NULL)
 {
 avformat_close_input(&pFormatCtx_Audio);
 pFormatCtx_Audio = NULL;
 }

 return 0;
}

DWORD WINAPI ScreenCapThreadProc( LPVOID lpParam )
{
 AVPacket packet;
 int got_picture;
 AVFrame *pFrame;
 pFrame=av_frame_alloc();

 AVFrame *picture = av_frame_alloc();
 int size = avpicture_get_size(pFormatCtx_Out->streams[VideoIndex]->codec->pix_fmt, 
 pFormatCtx_Out->streams[VideoIndex]->codec->width, 
 pFormatCtx_Out->streams[VideoIndex]->codec->height);

 avpicture_fill((AVPicture *)picture, picture_buf, 
 pFormatCtx_Out->streams[VideoIndex]->codec->pix_fmt, 
 pFormatCtx_Out->streams[VideoIndex]->codec->width, 
 pFormatCtx_Out->streams[VideoIndex]->codec->height);

 FILE *p = NULL;
 p = fopen("proc_test.yuv", "wb+");
 av_init_packet(&packet);
 int height = pFormatCtx_Out->streams[VideoIndex]->codec->height;
 int width = pFormatCtx_Out->streams[VideoIndex]->codec->width;
 int y_size=height*width;
 while(bCap)
 {
 packet.data = NULL;
 packet.size = 0;
 if (av_read_frame(pFormatCtx_Video, &packet) < 0)
 {
 continue;
 }
 if(packet.stream_index == 0)
 {
 if (avcodec_decode_video2(pCodecCtx_Video, pFrame, &got_picture, &packet) < 0)
 {
 printf("Decode Error.(解码错误)\n");
 continue;
 }
 if (got_picture)
 {
 sws_scale(img_convert_ctx, 
 (const uint8_t* const*)pFrame->data,
 pFrame->linesize, 
 0, 
 pFormatCtx_Out->streams[VideoIndex]->codec->height,
 picture->data,
 picture->linesize);

 if (av_fifo_space(fifo_video) >= size)
 {
 EnterCriticalSection(&VideoSection); 
 av_fifo_generic_write(fifo_video, picture->data[0], y_size, NULL);
 av_fifo_generic_write(fifo_video, picture->data[1], y_size/4, NULL);
 av_fifo_generic_write(fifo_video, picture->data[2], y_size/4, NULL);
 LeaveCriticalSection(&VideoSection);
 }
 }
 }
 av_free_packet(&packet);
 }
 av_frame_free(&pFrame);
 av_frame_free(&picture);
 return 0;
}

DWORD WINAPI AudioCapThreadProc( LPVOID lpParam )
{
 AVPacket pkt;
 AVFrame *frame;
 frame = av_frame_alloc();
 int gotframe;
 while(bCap)
 {
 pkt.data = NULL;
 pkt.size = 0;
 if(av_read_frame(pFormatCtx_Audio,&pkt) < 0)
 {
 continue;
 }

 if (avcodec_decode_audio4(pFormatCtx_Audio->streams[0]->codec, frame, &gotframe, &pkt) < 0)
 {
 av_frame_free(&frame);
 printf("can not decoder a frame");
 break;
 }
 av_free_packet(&pkt);

 if (!gotframe)
 {
 printf("没有获取到数据,继续下一次");
 continue;
 }

 if (NULL == fifo_audio)
 {
 fifo_audio = av_audio_fifo_alloc(pFormatCtx_Audio->streams[0]->codec->sample_fmt, 
 pFormatCtx_Audio->streams[0]->codec->channels, 30 * frame->nb_samples);
 }

 int buf_space = av_audio_fifo_space(fifo_audio);
 if (av_audio_fifo_space(fifo_audio) >= frame->nb_samples)
 {
 EnterCriticalSection(&AudioSection);
 av_audio_fifo_write(fifo_audio, (void **)frame->data, frame->nb_samples);
 LeaveCriticalSection(&AudioSection);
 }
 }
 av_frame_free(&frame);
 return 0;
}




Maybe there is another way to calculate PTS and DTS



I hope whatever the frame rate is,video playback speed is right.Not too fast or too slow.


-
Q&A : An interview with Matomo founder, Matthieu Aubry