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  • Playback : audio-video synchronization algorithm

    7 août 2016, par Rick77

    I’m in the process of creating a very basic video player with the ffmpeg libraries and I have all the decoding and re-encoding in place, but I’m stuck on audio video synchronization.

    My problem is, movies have audio and video streams muxed (intertwined) in a way that audio and video comes in "bursts" (a number of audio packets, followed by juxtaposed video frames), like this, where each packet has its own timestamp :

    A A A A A A A A V V V V A A A A A A A V V V V ...
    

    
A: decoded and re-encoded audio data chunk
    
V: decoded and re-encoded video frame

    supposedly in a way to prevent too much audio to be processed without video, and the other way around.

    Now I have to decode the "bursts" and send them to the audio/video playing components in a timely fashion, and I am a bit lost in the details.

    1. is there a "standard" strategy/paradigm/pattern to face this kind of problems ?
    2. are there tutorials/documentation/books around explaining the techniques to use ?
    3. how far can the muxing go in a well coded movie ?

    Because I don’t expect anything like this :

    AAAAAAAAAAA .... AAAAAAAAAAAAA x10000 VVVVVVVVVVVVVV x1000
    
audio for the whole clip followed by video

    or this :

    VVVVVVVVVVVV x1000 AAAAAAAAAAA...AAAAAAAAA x1000    
    
all video frames followed by the audio

    to happen in a well encoded video (after all, preventing such extremes is what muxing is all about...)

    Thanks !

    UPDATE : since my description might have been unclear, the issue is not with how the streams are, or about how to decode them : the whole audio/video demuxing, decoding, rescaling and re-encoding is set and sound, and each chunk of data has its own timestamp.

    My problem is what to do with the decoded data without incurring in buffer overrun and underrun and, generally, clogging my pipeline, so I guess it might be considered a "scheduling" problem.

  • how to record screen of windows using ffmpeg inside WSL [closed]

    12 avril 2024, par Santhosh

    I have WSL2 and ubuntu installed inside it.

    


    I have ffmpeg command line installed inside it.

    


    Now I am not sure how to record the screen. Can someone help me what command options to be used to record screen (including windows UI)

    


    I tried the below command.

    


    Opened powershell in windows, then entered into wsl and then ran the below command

    


     ffmpeg -f x11grab -y -framerate 30 -s 1920x1080 -i :0.0 -c:v libx264 -preset superfast -crf 18 out.mp4


    


    but it results in blank screen video

    


  • Android record video from multiple cameras and composite the multiple videos into one video

    22 mars 2024, par tonySilver

    Android Camera2 records video from multiple cameras, adds real-time timestamps to the frames captured by each camera, and finally composites the multiple videos into a single video file. does Android's native interface support these features ? Do I have to user FFMPEG to handle the frames captured by each camera

    


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