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• How to set frame offset for source and reference video for calculating using FFMpeg commandline ?

  1er septembre 2018, par Souvik Das

  I have a scenario where I am streaming a reference video on a server machine and receiving it at a client machine with exact same codec, using FFMpeg via UDP/RTP.

  So, I have a reference.avi file and a recording.ts file with me. Now, due to a network side issue and FFMpeg discarding old frames, often the recording.ts lacks exactly 12 FRAMES from the beginning. Sometimes, it may lack more frames in-between but that’d due to general network traffic and packet loss reason and I don’t plan to account for that. Anyways, due to those 12 frames, when I calculate the PSNR, it drops down to 13, even though remaining frames may/may not be affected.

  So, my aim is to discard first 12 frames from reference.ts and then compare. For that, I would also need to adjust the frames from recording.ts.

  Consider the following scenario :

  reference.ts has 1500 frames. So naturally I am going to cut-short it 1488. Then we have the following cases :

  1. recording.ts has 1500 frames. This is not affected. Still I will remove 12 frames to match the count. So frame 1 would then represent frame 13.
  2. recording.ts has 1496 frames. This is not affected. Still I will remove 12 frames even though it’d get to 1484 count assuming that frame 1 would then represent frame 13.
  3. recording.ts has 1488 frames. This is affected. No need to remove frames.
  4. recording.ts has 1480 frames. This is affected. No need to remove frames.

  Once that is done, then I will calcualte the PSNR. So, my FFMpeg should be able to do all this, hopefully in a single command on bash.

  A better alternative would be for FFMpeg to find the where the 13th frame is in recording.ts and then cut-short from the beginning. That’d be more preferred and even more if there is no cut-shorting required, i.e. if offset could be set in-line to command and no additional video output is generated for use in PSNR comparison.

  Current I am using the following command to calculate the PSNR.

  ffmpeg -i 'recording.ts' -vf "movie='reference.avi', psnr=stats_file='psnr.txt'" -f rawvideo -y /dev/null

  It’d be great if somebody could help me in this regard. Thanks.

• OpenCV video capture - output even potentially corrupt frames

  20 juillet 2018, par J. S.

  In FFmpeg, there is a flag "output_corrupt" that allows the command to output even corrupted frames. I am sending h264 stream to a server where its first few frames are corrupted. By setting "output_corrupt" flag in my FFmpeg command, I am able to view the live stream.
  I can see the live stream by piping FFmpeg data to OpenCV VideoCapture (i.e. cv2.VideoCapture(’/dev/stdin’))

  Note : since my plan is to run CV algorithms on those frames, I need to be able to run it on OpenCV.

  However, by not directly sending the data through VideoCapture, it unavoidably causes some latency issue.

  The best scenario would be to just directly send the h264 stream to OpenCV VideoCapture (i.e. cv2.VideoCapture(’udp ://......’))
  However, because of the corrupted frames, the OpenCV script gets stuck after a second.

  Is there any way to run OpenCV VideoCapture such that it still outputs potentially corrupt frames ?

  Thank you.

• Error while installing ffmpeg on standalone computer

  10 juillet 2018, par newuser

  I am trying to install libx264 and ffmpeg on a computer without internet access
  My plan is to first download all required packages and dependencies on a laptop with internet and then copy them over
  To download the packages I used :

  apt-get download $(apt-rdepends <package>|grep -v "^ ")
  
  </package>

  I was able to install yasm, libvpx and libx264 without issues this way.
  When I try to install ffmpeg, I get this error.

  The following packages have unmet dependencies:
  
   chromium-codecs-ffmpeg-extra-dbg : Depends: chromium-codecs-ffmpeg-extra (= 51.0.2704.79-0ubuntu0.16.04.1.1242) but 66.0.3359.181-0ubuntu0.16.04.1 is installed
  
   ffmpeg-dbg : Depends: ffmpeg (= 7:2.8.14-0ubuntu0.16.04.1)
  
   ffmpeg-doc : Depends: libjs-bootstrap but it is not installed
  
   ffmpeg2theora : Depends: liboggkate1 (>= 0.3.0) but it is not installed
  
   ffmpegthumbs : Depends: libkf5kiowidgets5 (>= 4.99.0) but it is not installed
  
   kffmpegthumbnailer : Depends: libkio5 (>= 4:4.3.4) but it is not installed
  
   moc-ffmpeg-plugin : Depends: moc (= 1:2.6.0~svn-r2788-1) but it is not installed

  where do I get these packages from ? I dont want apt-get to download them for me as I want to be able to get the package files.