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• How do I use ffmpeg to extract the total time of a video slice without actually producing the video slice ?

  18 juin 2022, par iChux

  


  I have a video named 'ev.mp4'. Slice the video into segments :

  


  


  # COMMAND 1
ffmpeg -i "ev.mp4" -c copy -map 0 -segment_time 15 -g 9 \
    -sc_threshold 0 -force_key_frames "expr:gte(t,n_forced*9)" \
    -reset_timestamps 1 -f segment ev-%04d.mp4

ev-0000.mp4
ev-0001.mp4
ev-0002.mp4


  


  


  Get each segment time

  


  


  # COMMAND 2
for f in ev-*.mp4;
do
    echo $f == $(ffprobe -v error -show_entries \
    format=duration -of default=noprint_wrappers=1:nokey=1 $f);
done;

ev-0000.mp4 == 17.251000
ev-0001.mp4 == 17.918000
ev-0002.mp4 == 10.444000


  


  


  I am only able to extract the duration of each sliced segment after the videos have existed in a sliced format on the hard drive e.g. ev-0000.mp4

  


  


  My question : is it possible to get the duration of each slice from COMMAND 1 such that instead of producing the sliced files, I will get the duration of each slice ?

  


• Slightly different number of total frames between my program (using libav) and ffprobe

  16 juin 2022, par Alvein

  For learning purposes, I made a routine that decodes each frame for each stream inside a given container.

  


  I noticed that for some videos, the amount of frames returned by my code differs the one calculated by the tool ffprobe (which comes with ffmpeg).

  


  I'm using ffprobe like this :

  


  ffprobe <media file="file"> -v error -select_streams v:0 -count_frames -show_entries stream=nb_read_frames&#xA;</media>

  


  Replacing "v:0" with "a:0" for audio, etc.

  


  And this is my source code :

  


  void showFrames(char *szFilename) {
    int               iError;
    char              szError[AV_ERROR_MAX_STRING_SIZE];
    AVFormatContext   *fcFormatCtx;
    AVCodec           *cdCodec;
    AVCodecParameters *cdpCodecParams;
    AVCodecContext    *ccCodecCtx;
    AVPacket          *pkPacket;
    AVFrame           *frFrame;
    fcFormatCtx=avformat_alloc_context();
    iError=avformat_open_input(&fcFormatCtx,szFilename,NULL,NULL);
    if(0>iError) {
        av_strerror(iError,szError,sizeof(szError));
        fprintf(stderr,"avformat_open_input() failed: %s\n",szError);
        return;
    }
    iError=avformat_find_stream_info(fcFormatCtx,NULL);
    if(0>iError) {
        av_strerror(iError,szError,sizeof(szError));
        fprintf(stderr,"avformat_find_stream_info() failed: %s\n",szError);
        avformat_close_input(&fcFormatCtx);
        return;
    }
    for(uint uiSt=0;uiStnb_streams;uiSt++) {
        cdpCodecParams=fcFormatCtx->streams[uiSt]->codecpar;
        cdCodec=avcodec_find_decoder(cdpCodecParams->codec_id);
        if(NULL==cdCodec) {
            fprintf(stderr,"no codec found for stream %u\n",uiSt);
            continue;
        }
        fprintf(stderr,"stream %u\n",uiSt);
        if(AVMEDIA_TYPE_VIDEO==cdpCodecParams->codec_type)
            fprintf(stderr,"video codec id=%d name='%s'\n",
                    cdCodec->id,cdCodec->long_name);
        else if(AVMEDIA_TYPE_AUDIO==cdpCodecParams->codec_type)
            fprintf(stderr,"audio codec id=%d name='%s'\n",
                    cdCodec->id,cdCodec->long_name);
        else {
            fprintf(stderr,"unsupported codec id=%d name='%s'\n",
                    cdCodec->id,cdCodec->long_name);
            continue;
        }
        ccCodecCtx=avcodec_alloc_context3(cdCodec);
        avcodec_parameters_to_context(ccCodecCtx,cdpCodecParams);
        iError=avcodec_open2(ccCodecCtx,cdCodec,NULL);
        if(0>iError) {
            av_strerror(iError,szError,sizeof(szError));
            fprintf(stderr,"avcodec_open2() failed: %s\n",szError);
            avcodec_free_context(&ccCodecCtx);
            continue;
        }
        pkPacket=av_packet_alloc();
        frFrame=av_frame_alloc();
        av_seek_frame(fcFormatCtx,uiSt,0,AVSEEK_FLAG_FRAME);
        while(0==av_read_frame(fcFormatCtx,pkPacket)) {
            if(uiSt==pkPacket->stream_index) {
                iError=avcodec_send_packet(ccCodecCtx,pkPacket);
                if(0>iError) {
                    av_strerror(iError,szError,sizeof(szError));
                    fprintf(stderr,"avcodec_send_packet() failed: %s\n",szError);
                    break;
                }
                while(true) {
                    iError=avcodec_receive_frame(ccCodecCtx,frFrame);
                    if(0>iError)
                        break;
                    fprintf(stderr,"stream %u, frame %d\n",
                            uiSt,ccCodecCtx->frame_number);
                    av_frame_unref(frFrame);
                }
                if(AVERROR(EAGAIN)!=iError&&AVERROR_EOF!=iError) {
                    av_strerror(iError,szError,sizeof(szError));
                    fprintf(stderr,"avcodec_receive_frame() failed: %s\n",szError);
                    break;
                }
            }
            av_packet_unref(pkPacket);
        }
        av_packet_free(&pkPacket);
        av_frame_free(&frFrame);
        avcodec_free_context(&ccCodecCtx);
    }
    avformat_close_input(&fcFormatCtx);
}


  


  It's pretty much self contained but you may ignore all the initializations and go directly to the while after the call to av_seek_frame(). This is where the actual frames are being read.

  


  BTW, I'm using av_seek_frame() because this program goes stream by stream, separating the frames, so I need to rewind with every stream found.

  


  Anyway, I've tested the previous code with the following files :

  


  #1. sample-10s.mp4 from https://samplelib.com/sample-mp4.html ...

  


  


  My program : 301 video frames ; 440 audio frames

  


  ffprobe : 303 video frames ; 440 audio frames

  


  


  #2. production ID_3997798.mp4 from https://www.pexels.com/video/hands-hand-table-colorful-3997798/ ...

  


  


  My program : 736 video frames ; no audio frames

  


  ffprobe : 738 video frames ; no audio frames

  


  


  I found more videos with this difference, but it ONLY happens in the video streams.

  


  Is there something I am forgetting ? There seem to be always 2 frames behind what ffprobe shows.

  


  Thank you.

  


• avformat/demux : allow total size of packets in raw_packet_buffer to reach probesize

  7 novembre 2021, par Marton Balint

  avformat/demux : allow total size of packets in raw_packet_buffer to reach probesize
  Previously this was hardcoded to 2500000 bytes, so probing of the stream codecs
  
  was always limited by this, and not probesize.
  Also keep track of the actual size of packets in raw_packet_buffer and not the
  
  remaining size for simplicity.
  Fixes ticket #5860.
  Signed-off-by : Marton Balint <cus@passwd.hu>
  

  • [DH] libavformat/demux.c
  • [DH] libavformat/internal.h
  • [DH] libavformat/options.c
  • [DH] libavformat/utils.c