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• Why doesn't FFmpeg work when using yt-dlp in python script ?

  11 mai 2022, par spelle

  I'm trying to download a video using yt-dlp in python.

  


  ydl_opts = {'format': 'bv+ba/b'}
with YoutubeDL(ydl_opts) as ydl:
     ydl.download('https://www.reddit.com/r/cats/comments/re37dn/weve_been_feeding_this_stray_for_several_years/')


  


  But I'm reaching an FFmpeg error in the log

  


  [generic] 1o8t9ollwx481: Requesting header
[redirect] Following redirect to https://www.reddit.com/r/cats/comments/re37dn/weve_been_feeding_this_stray_for_several_years/
[Reddit] re37dn: Downloading JSON metadata
[Reddit] re37dn: Downloading m3u8 information
[Reddit] re37dn: Downloading MPD manifest
[info] 1o8t9ollwx481: Downloading 1 format(s): dash-video_4419291+dash-audio_0_133951
WARNING: You have requested merging of multiple formats but ffmpeg is not installed. The formats won't be merged.
[download] Destination: We’ve been feeding this stray for several years, but she’s lost a lot of weight and I don’t think she would last outside for another winter, so I brought her in. [1o8t9ollwx481].fdash-video_4419291.mp4
[download] 100% of 5.18MiB in 00:00               
[download] Destination: We’ve been feeding this stray for several years, but she’s lost a lot of weight and I don’t think she would last outside for another winter, so I brought her in. [1o8t9ollwx481].fdash-audio_0_133951.m4a
[download] 100% of 161.32KiB in 00:00


  


  FFmpeg is installed through pip and added in PATH.

  


• lavu/riscv : add optimisations

  12 septembre 2022, par Rémi Denis-Courmont

  lavu/riscv : add <intmath.h> optimisations
  This provides some micro-optimisations for signed integer clipping, and
  
  support for bit weight with the Zbb extension.
  

  • [DH] libavutil/intmath.h
  • [DH] libavutil/riscv/intmath.h

• How to extract fully synced audio with ffmpeg ?

  2 janvier 2023, par Brendan Hill

  I have an MP4 file with video and audio. I need to extract the audio stream only to an MP3 file.

  


  However it is critical for our application that the timing / synchronization of the audio file is exactly aligned with the original video, as we cross-correlate audio features based on timing.

  


  I currently use this command :

  


  ffmpeg -y 
   -v error 
   -map 0:a ./the-output-file-mp3
   -map 0:v ~/a-dummy-video-output-file.mp4
   -i ~/the-input-file.mp4
   -acodec copy 
  


  


  as I read somewhere that mapping both 0:a and 0:v would guarantee alignment & synchronization. I then discard the video file as it is not needed.

  


  However it is orders of magnitude faster to just extract the audio instead :

  


  ffmpeg -y 
   -v error 
   -map 0:a ./the-output-file-mp3
   -i ~/the-input-file.mp4
   -acodec copy 


  


  But I don't know if this guarantees alignment, because I read on this page that :

  


  If you only extract audio from a video stream, the length of the audio may be shorter than the length of the video. To make sure this doesn't happen, extract both audio AND video with the same call to ffmpeg, e.g. "ffmpeg -i vid.avi -map 0:a audio.wav -map 0:v onlyvideo.avi

  


  However perhaps I am putting too much weight on that comment. I don't care if the audio clip finishes early, but it is critical that it does not start late, or get de-synced from the original video at any point.

  


  What is the most efficient way with ffmpeg to extract the audio stream with a guarantee that it is 100% aligned in time to the video (and starts at exactly the same time) ?

  


  Will this method guarantee alignment ?

  


  ffmpeg -y 
   -v error 
   -i ~/the-input-file.mp4
   -vn
   -acodec copy 
   ~/the-output-file.mp4