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• How to accurately match an image to a video frame and exit with ffmpeg

  10 avril 2020, par Hans J

  In Bash,
I am trying to match an image to a frame in ffmpeg. I also want to exit the ffmpeg process when the match is found. Here is a (simplified version) of the code currently :

  



  ffmpeg --hide_banner -ss 0 -to 60 \
-i "video.mp4" -i "image.jpg" -filter_complex \
"blend=difference, blackframe" -f null - null 2>log.txt &
pid=$!
trap "kill $pid 2>/dev/null" EXIT
while kill -0 $pid 2>/dev/null; do
     # (grep command to monitor log file)
     # if grep finds blackframe match, return blackframe time
done


  



  To my understanding, if the video actually contains a blackframe I will get a false-positive. How can I effectively mitigate this ?

  



  While this is unnecessary to answer the question, I would like to exit the ffmpeg process without having to use grep to constantly monitor the log file, instead using pure ffmpeg

  



  Edit : I say this because while I understand the blend filter is computing the difference, I am getting a false positive on a blackframe in my video and I don't know why.

  



  Edit : A possible solution to this issue is to not use blackframe at all, but psnr (Peak Signal to Noise Ratio) but normal usage is by comparing two videos frame by frame, and I don't know how to effectively use it with an image as input.

  


• How do I half the frame-rate of a DNxHR mxf file with FFMpeg losslessly ?

  19 mai 2020, par in03

  I have limited experience with FFMpeg, so there's a chance I'm missing something simple here. Imagine the following scenario :

  



  I have a DNxHR HQ UHD 50P .mxf file, 10 seconds/500 frames long. I want to remove every second frame from this file with FFMpeg so that I end up with a DNxHR HQ UHD 25P .mxf file, 10 seconds/250 frames long.

  



  I do not want the file to be re-encoded in any way and any audio streams should remain untouched. I imagine this is possible since DNxHR is an intra-frame codec. If this isn't possible with FFMpeg, I'm happy to hear alternative approaches with similar tools.

  



  I last tried the following command ffmpeg -i TEST.mxf -r 25 -c:v copy TEST_25P.mxf. Which retains the original duration of the file, halves the frame-rate, bitrate and frame-count as expected, but does so by slowing the clip down to half-speed and keeping the file at the same duration, effectively deleting the 2nd half of the file...

  



  Any suggestions area appreciated.

  



  EDIT :

  



  I am exporting files from DaVinci Resolve which can only export files at the project's locked framerate. We edit in 50P because at some point we will upgrade our platform to serve 50P content, but for the time being we can only serve 25P. Converting our 50P deliverables to 25P is much easier than converting 25P projects to 50P projects.

  


• Recording live stream with intermittent no audio with FFmpeg

  15 décembre 2022, par charlie-bird

  I'm trying to record a live stream with ffmpeg and having an issue with the audio.
The stream has video and audio, until it goes to video only for a few minutes and back to audio+video.
  
A : XXXXXX________YYYYYY_______ZZZZZZ
  
V : XXXXXXOOOOO0YYYYYYOOOOOZZZZZZ
  

  


  When I stop the recording and look at the output file, the absence of audio is messing stuff up. Instead of having no audio during the "breaks" ffmpeg wrote the audio track from after the break over the video, completely disconnecting audio and video
  
A : XXXXXXYYYYYYYZZZZZZZZZ
  
V : XXXXXXOOOOOOOOYYYYYYOOOOOOOZZZZZZ
  

  


  Is there an argument or parameter to force the recording of an "empty" audio track over the video when there's no audio, to keep both in sync ?

  


  Right now, not using any options

  


  ffmpeg -i "https://input.m3u8" ~/Outputfile.mp4


  


  Tried with map as below, same issue

  


  ffmpeg -i "https://input.m3u8" -map 0:a -map 0:v ~/Outputfile.mp4


  


  EDIT :
Also tried with a simple copy, in that case the audio stops but then isn't recorded when it comes back

  


  ffmpeg -i "https://input.m3u8" -map 0:a -map 0:v -c copy ~/Outputfile.ts


  


  EDIT 2 :
I've found a workaround. I re-stream the live stream using VLC on a local port and record copy with ffmpeg, and now it's all in sync

  


  ffmpeg -i "http://10.10.10.10:1234" -c copy ~/Outputfile.ts


  


  I would still like to be able to do this directly, but in the meantime that works.