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• Detect scene change on part of the frame

  16 juin 2021, par user18130814200115

  I have a video file of an online lecture cosisting of a slideshow with audio in the background.
  
I want to save images of each slide as well as the timestamp of that slide.
I do this using the scene and metadata filters :

  


  ffmpeg -i week-01.mp4 -filter_complex "select='gt(scene,0.011)',metadata=print:file=frames/time.txt" -vsync vfr frames/img%03d.jpg


  


  This works fine exept for one thing, there is a timer onscreen on the right in the video file.
If i set the thershold small enough to pick up all the slide changes, it also picks up the timer changes.

  


  So here is my question, Can I ask ffmpeg to :

  


  

  1. analize part of the frame (only the right side till roughly 75% to the left).

  


  2. Then, on detecting a scene change in this area, save the entire frame and the timestamp.

  


  


  I though of making a script that

  


  

  1. crops the video and saves it alongside the origional

  


  2. analize the cropped video for scene changes and save the timestamps

  


  3. extract the frames from the origional video using the timestamps

  


  


  Is there a better/faster/shorter way to do this ?
Thanks in advance !

  


• FFMpeg - how to encode a F4M manifest file to mp4

  20 novembre 2015, par Roee

  I’m working on a project, where we want to encode flash videos to mp4 (for example, we want to encode a f4v file), and live-stream them (which means we can’t just download all the f4f files, then encode them to a single mp4 and just then stream it. The encoding and streaming has to be done while downloading the files).

  If the format of the flash video is flv for example, FFMpeg can do what I’ve described without any problem. I just give the address of the flv file to FFMpeg, and it encodes and streams it as mp4.

  But, if the format of the flash video is something more complicated as f4v (which gets downloaded as many f4f files), I don’t have a single url to give to FFMpeg as input - I have many addresses of f4f files. I don’t even know how many f4f files the video has before playing it - it looks like the flash player just fetches the next f4f file when needed.

  I read online that there is a manifest file (its extension is f4m), that "describes" to the flash player which f4f files it should download and play, and what’s their playing-order and everything.

  My question is - if I have the url of this f4m file, what should I do in order to encode all its f4f files to mp4 ?
  I’ve tried to give to FFMpeg just the f4m file as input, but it doesn’t know what to do with it...

  I’ll really appreciate any response that might help, as I’ve been working on this issue for few days now and I still haven’t found any answer...

  Thanks,
  Roee.

• FFmpeg command to add a single frame to the end of a video not working (resulting in zero-byte output file)

  21 juillet 2023, par Frost Dream

  I'm trying to add a single frame to the end of a video file without re-encoding using FFmpeg. After searching online, I came across a command that is supposed to achieve this using the concat demuxer. However, when I run the command, it only creates a zero-byte output file. I'm not sure what I'm doing wrong.

  


  Here's the command I'm using :

  


  ffmpeg -i input_video.mp4 -framerate 30 -loop 1 -i single_frame.png -filter_complex "[0:v][1:v]concat=n=2:v=1:a=0" -c:v libx264 -preset veryfast -crf 18 -c:a copy output_video.mp4


  


  The input_video.mp4 is the path to my original video file, and single_frame.png is the path to the image file containing the single frame I want to add. I expected the output video, output_video.mp4, to contain the original video followed by the single frame at the end, but it's just a zero-byte file.

  


  Am I missing something in the command ? Is there an issue with the concat demuxer approach for adding a single frame ? Any insights or alternative methods to achieve this would be greatly appreciated.

  


  Thank you !