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• Python script creates too short video using ffmpeg

  25 mai 2014, par Majzlik

  I use python script to create multiple pictures and call ffmpeg to create video. But there is a problem, because ffmpeg use just few pictures (about 7 - 10 from 160), but throws no error. I’ve tried the same command from commandline and video was correct. I’m calling ffmpeg this way :

  ffmpeg_call = ["ffmpeg", "-r", str(FPS), "-b", "16777216", "-y", "-i", "./sample_%05d.png", FILEOUTNAME + ".mp4"]
  
  subprocess.call(ffmpeg_call)

  and this was command in commandline :

  ffmpeg -r 25 -b 16777216 -y -i ./sample_%05d.png animation.mp4

  I’ve printed these commands to compare and they were the same, so there has to be problem in ffmpeg + python cooperation. Don’t you know, how to fix it ?

  UPDATE :

  this is log from ffmpeg :

  ffmpeg version 0.8.10-4:0.8.10-0ubuntu0.12.04.1, Copyright (c) 2000-2013 the Libav     developers
  
    built on Feb  6 2014 20:56:59 with gcc 4.6.3
  
  *** THIS PROGRAM IS DEPRECATED ***
  
  This program is only provided for compatibility and will be removed in a future release. Please use avconv instead.
  
  Input #0, image2, from '/tmp/tmpRKxT6s/ampgraph/tmp/sample_%05d.png':
  
  Duration: 00:00:00.44, start: 0.000000, bitrate: N/A
  
  Stream #0.0: Video: png, pal8, 640x480, 25 fps, 25 tbr, 25 tbn, 25 tbc
  
  Incompatible pixel format 'pal8' for codec 'mpeg4', auto-selecting format 'yuv420p'
  
  [buffer @ 0x19e18a0] w:640 h:480 pixfmt:pal8
  
  [avsink @ 0x19ee1c0] auto-inserting filter 'auto-inserted scaler 0' between the filter 'src' and the filter 'out'
  
  [scale @ 0x19e2fc0] w:640 h:480 fmt:pal8 -> w:640 h:480 fmt:yuv420p flags:0x4
  
  Output #0, mp4, to './ampgraph/animation.mp4':
  
    Metadata:
  
      encoder         : Lavf53.21.1
  
      Stream #0.0: Video: mpeg4, yuv420p, 640x480, q=2-31, 200 kb/s, 25 tbn, 25 tbc
  
  Stream mapping:
  
    Stream #0.0 -> #0.0
  
  Press ctrl-c to stop encoding
  
  frame=   11 fps=  0 q=2.5 Lsize=      46kB time=0.44 bitrate= 859.1kbits/s    
  
  video:45kB audio:0kB global headers:0kB muxing overhead 1.906569%

• ffmpeg libav swap output file [on hold]

  16 février 2018, par themadmax

  I writing streaming video into disk, and I want to swap output file

  while(!stop) {
  
      int error = av_read_frame(formatCtxPtr_.get(), packetPtr.get());
  
      if (error<0)
  
          break;
  
      if (packetPtr->stream_index == videoStreamIndex_) {
  
          AVPacket *ppkt = av_packet_clone(packetPtr.get());
  
          AVPacket& pkt = *ppkt;
  
          auto in_stream = formatCtxPtr_->streams[pkt.stream_index];
  
          pkt.stream_index = 0 ; //Only on output stream video index = 0
  
          auto out_stream = fmtCtxOutputPtr_->streams[pkt.stream_index];
  
          pkt.pos = -1;
  
          int ret = av_interleaved_write_frame( fmtCtxOutputPtr_.get(), &pkt );
  
          if ( swap_ /*&& (AV_PKT_FLAG_KEY & pkt.flags)*/ ) { //Never have keyframe
  
              swap_ = false ;
  
              av_write_trailer(fmtCtxOutputPtr_.get());
  
              avio_flush(fmtCtxOutputPtr_->pb);
  
              avio_close(fmtCtxOutputPtr_->pb);
  
              //Reset stream time
  
              out_stream->start_time = out_stream->duration = out_stream->first_dts = out_stream->cur_dts = out_stream->info->last_dts = AV_NOPTS_VALUE ;
  
              int error = avio_open(&fmtCtxOutputPtr_->pb, "stream2.mp4", AVIO_FLAG_WRITE);
  
              error = avformat_write_header( fmtCtxOutputPtr_.get(), NULL );              
  
          }
  
      }
  
  }

  I have not error, write_frame return 0, "stream2.mp4" is create but still at 0 byte

• Read Per-Frame Timecode with FFMPEG ?

  3 novembre 2019, par DiB

  I want to read a per-frame timecode out of a video file using libav (FFMPEG). I’ve started by digging into FFProbe. Using this as a starting point for my code, I can get to the AVStream that has the timecode in it. From there, I can use the dictionary to look at the stream’s metadata.

  int show_stream(WriterContext *w, AVFormatContext *fmt_ctx, int stream_idx, InputStream *ist, int in_program)
  
  {
  
    AVStream *stream = ist->st;
  
  ...
  
    auto tcr = av_dict_get(stream->metadata, "timecode", NULL, 0);
  
    std::cerr << "Timecode: " << tcr->value << ", Total Frames: << stream->nb_frames << "\n";

  The time code is the correct one that was embedded into the video. The nb_frames is correctly the total number of video frames that I have. What I can’t get is the per-frame timecode. I don’t want to compute it if I don’t have to, I want to know exactly what was stamped on each frame. Is this possible ?

  // Pseudocode for what I want
  
  for(const auto& f : allOfMyFrames)
  
  {
  
    std::cerr << "Frame number " << f.number << ", Timecode: " << f.timecode << "\n";
  
  }