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• How to resize yuv420sp using FFmpeg

  27 juin 2012, par newentry

  How to resize yuv420sp data into some other resolution.I tried using ffmpeg sws_scale but no success.I tried by converting yuv420sp to yuv420p and then tried to resize yuv420p into RGB24 via sws_scale but the things it works when both src and destination width and height are same, but for different resolution didn't get correct rgb24. Can anyboody guide me with example code using c or if possible through Java itself .The final resized data must be in yuv420p.
  In my case i am trying to downsize the yuv420sp for eg 640*480 to 320*240 or 176*144.

  thanks,

• FFMPEG doesn't decode the first few frames with multithreaded decoding. C++

  12 octobre 2022, par Patrick McKeever

  So to get better decoding speeds, I'm setting

  


  av_stream->codec->thread_count = 32;
av_stream->codec->thread_type = FF_THREAD_FRAME;


  


  This greatly improves decoding time, but seems to lose some frames (equaling the amount of threads I set)

  


  For the first 32 or so frames, av_readframe(), and avcodec_send_packet() succeed, but avcodec_recieve_frame() seems to fail.

  


  This seems to result in the last 31 frames to not be decoded, as my loop exits once avcodec_send_packet() fails.

  


  Anyone know how I can get the final frames to also be decoded ? I read something about flushing the buffers, but I'm not really sure how to do that.

  


  Thanks.

  


• Concatenate audio parts of different videos with ffmpeg [migrated]

  15 août 2024, par Swike

  So I have two videos :

  


  

  • Vid_eng.mkv is a high resolution video that has the audio in English.

  


  • Vid_esp.mkv is a low resolution video that has the audio in Spanish.

  


  


  Both videos are showing more or less the same stuff but the difference is that the Spanish one has the intro and outro cut out (the first 66 seconds are missing).

  


  I want to create a new video file, Vid_out.mkv that has the Vid_eng.mkv video and both audios (so the final file has multistream audio). The issue is that the Spanish audio will not be in sync with the high resolution video, so what I did was this :

  


  ffmpeg -i Vid_eng.mkv
       -f lavfi -t 66 -i anullsrc -i Vid_esp.mkv
       -filter_complex "[1:a][2:a]concat=n=2:v=0:a=1[outa]"
       -map 0 -map "[outa]"
       -metadata:s:a:0 language=eng
       -metadata:s:a:1 language=spa
       -disposition:a:1 default
       -c:v copy Vid_out.mkv


  


  What I'm doing here is essentially creating the new Vid_out.mkv using the video from Vid_eng.mkv, the audio multistream from both Vid_eng.mkv and Vid_esp.mkv, but with the twist that the audio from Vid_esp.mkv is actually beginning 66 seconds later (so that it is synced with the English video). I did this by adding 66 seconds of silence (with -f lavfi -t 66 -i anullsrc) and concatenating that silence with the Spanish audio (with -filter_complex "[1:a][2:a]concat=n=2:v=0:a=1[outa]") before adding this concatenated audio stream to the final file as the secondary audio. Also I included some metadata to know the which audio is which.

  


  Everything good for the moment. But now I wanted to try something more sophisticated : instead of having 66 seconds of silence concatenated to the Spanish audio I want 66 seconds of the English audio (the audio from Vid_eng.mkv), then the audio from Vid_esp.mkv, and finally when the Spanish audio has finished and the video is still going, I want the English audio again. So, instead of silence at the beginning and end of the video when played with the secondary audio stream, what I want is the English audio to play. How can I do that with ffmpeg ?

  


  ---

  


  For reference I've been following ideas from these answers :

  


  

  • How to add audios from different videos into one multistream video

  


  • How to add a few seconds of silence to an audio