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• How to configure AVStream to write 29.97FPS files using FFmpeg

  14 mai 2018, par vtruant

  I’m trying to write mkv file using ffmpeg to encode in FFV1 and FLAC in NTSC format, but the frame rate shown in VLC and media info are not correct.

  Here is how I create and configure the output format context :

  AVOutputFormat  *outputFormat = av_guess_format("matroska", NULL, NULL);
  
  
  
  //Allocate an AVFormatContext for an output format.
  
  int err = avformat_alloc_output_context2(&_formatContext, outputFormat, NULL, filename);
  
  
  
  //Specify the codec of the outputFormat
  
  _formatContext->oformat->video_codec = _videoCodecContext->codec_id;
  
  
  
  //Create AVStream 
  
  AVStream *videoStream = avformat_new_stream(_formatContext, NULL);  
  
  
  
  //FrameDuration.value : 1001, FrameDuration.timescale : 30000
  
  videoStream->time_base = (AVRational){ (int)_frameDuration.value, (int)_frameDuration.timescale };  //1001 30000
  
  
  
  //Copy video stream parameters to the muxer
  
  err = avcodec_parameters_from_context(videoStream->codecpar, _videoCodecContext);
  
  
  
  //Open file for writing
  
  err = avio_open(&_formatContext->pb, filename, AVIO_FLAG_WRITE);            
  
  
  
  if (err >= 0) {
  
      //Write header
  
      err = avformat_write_header(_formatContext, &options);
  
  }

  Before writing the packet, I use this to convert PTS to the stream time_base

  // Rescale output packet timestamp values from codec to stream timebase
  
  av_packet_rescale_ts(inAVPacket, *inTimeStamp, [outputStream stream]->time_base);

  The thing is that the avformat_write_header method is changing the stream time_base from 30000/1001 to 1/1000, so PTS loose precision. In VLC inspector, the frame rate shown is 1000 fps and in MediaInfo 30.033 fps.

  The file is playing correctly and the video/audio sync is OK.

  Is there something to do to specify the file frame rate somewhere else ?
  Or a work around to avoid changing the time_base when calling avformat_write_header ?

• Image orientation chaning while making image from a video using ffmpeg [on hold]

  19 janvier 2016, par rakeshp

  I am making image thumbnails from video on Linux, but for some videos the orientation is changing and not coming as per the original video orientation. Here is my code.

  ffmpeg -itsoffset 4 -i test_video.mov -ss 00:00:01.000 -vf scale=-1:240 -vframes 1 test_image.png

  I tried with multiple options like adding "-vf transpose=1 " to the above code, but still it didn’t work for me.Can anyone help me here.

• Creating a video from single image and update when image changes ?

  16 novembre 2016, par BugHunterUK

  I’m trying to use ffmpeg to convert a single image into an mp4. I’ve got it to work with the following command :

  ffmpeg -re -loop 1 -i ./cam.jpg -r 10 -vcodec mpeg4 -f mpegts cam.mp4

  But if I open cam.jpg, modify it by changing the text, and save as cam.jpg the video doesn’t change to reflect the modification.

  Is this possible with ffmpeg ?