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• FFMPEG - How to Extract Frames As Images While Removing Sequentially Duplicate Frames

  19 mars 2017, par Michael Nelson

  Is there any way (via script or preferably some parameter in calling ffmpeg that I missed) to extract frames from an avi file and ignore sequentially duplicate frames, thus being able to go through the pictures looking only at the deltas/changes ?

  I frequently have to record meetings at work and a lot of the time, the client screen that I am looking at is not changing while we are talking over the phone. After the meeting is over, I need to use these images as part of our documentation and specifications gathering.

  I know that I could just output every frame and run them through any given duplicate file remover utility, but this would remove ALL duplicate frames. So, if the frames extracted went like this :

  A, A, A, B, B, B, B, C, C, A, A, C, C, C, B, B, B ...

  Running them through a typical duplicate file remover, I would get : A, B, C

  What I would want is : A, B, C, A, C, B

  The command that I am currently using to extract the images is :

  ffmpeg.exe -i file.avi -ss 0 -sameq -f image2 -r 1 images%5d.png

  I was getting every frame beforehand (removing the -r 1 from above), but that was generating way too many frames to deal with since these online meetings can go for hours, so for now, I get one frame per second from the file.

  A Windows based solution would be preferable, however, I’m sure other people would be interested in solutions on other platforms if available.

  Any solution or point in the right direction is much appreciated.

• FFmpeg efficient capture from rtsp ipcamera

  29 août 2020, par Jax2171

  I need to capture an audio/video rtsp stream uncompressed in a file from ipcamera. Audio (pcm_alaw) and video (h264) must be synchronized. It is necessary that the file does not get corrupted if the camera loses the connection for a few moments (mp4).

  


  At the moment I use the command below, but the ts codec does not support pcm_alaw and therefore the audio is not heard :

  


  ffmpeg -stimeout 2000000 -rtsp_transport tcp -i rtsp://admin:1234@192.168.5.22/h264 -c:v copy -c:a copy -f mpegts -y main.ts


  


  I use the mpegts codec because I need to check the duration of the capture in real time with the command :

  


  ffprobe -i /home/pi/NAS/main.mov -show_entries format=duration -v quiet -of csv="p=0"


  


  If i use mkv or avi its output would be :

  


  N/A


  


  The verification of the duration is important because I capture files of about 3 hours and at my choice I perform some data while the capture is in progress. I prefer not to compress the audio because I have often noticed some asynchrony with respect to the video when cutting.

  


  Thank you.

  


• Audio out of sync after merging video chunks extracted with ffmpeg using -c copy and -reset_timestamps 1 [closed]

  8 décembre 2024, par Tree

  I’m splitting a long video (around 2 hours) into smaller chunks using ffmpeg commands like :

  


  ffmpeg -i input.mp4 -ss START_SECOND -t LENGTH -c copy -reset_timestamps 1 -y chunk_X.mp4


  


  Then, I’m concatenating the resulting chunks using a concat list file :

  


  ffmpeg -f concat -safe 0 -i list.txt -c copy -y merged_output.mp4


  


  So the chunks always come from the same file, and have the same codec/size/bitrate.

  


  My goal is to avoid re-encoding the entire video to keep the process fast. However, I’m noticing that after the final merge, the audio in some parts of the merged video is out of sync with the video. The first chunk seems fine, but from the second chunk onward, the audio often drifts out of sync.

  


  What could be causing the audio desynchronization, and how can I correctly extract and merge the chunks without losing A/V sync, while still avoiding a full re-encode ?

  


  I tried to first pass in -ss before -i to cut on keyframes, but I get the same result.