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• How to use ffmpeg to encode isolated motion vectors (using codecview)

  22 juillet 2021, par Temmeh

  I have been successfully using this command to superimpose MPEG motion vectors onto a video :

  


  ffmpeg -v error -flags2 +export_mvs -i input.mp4 -vf codecview=mv=pf+bf+bb -y output.mp4

  


  Now I would like to be able to export an h264 mp4 of just the motion vector arrows, like in this example, without the original video layered underneath. I checked the codecview documentation and and did not find a flag or option to do this.

  


  Any help is appreciated !

  


• Python script and equivalent command do not run the same

  19 août 2021, par user32882

  I would like to use youtubedl to download the audio from a YouTube video into an mp3 file. I came up with the following command to do so :

  


  youtube-dl -x --audio-format mp3 https://www.youtube.com/watch?v=SF8DGbfOFig&ab_channel=derang

  


  When I run the above command through my command line, it seems that I successfully manage to download the file in mp3 format :

  


  [youtube] SF8DGbfOFig: Downloading webpage
[download] Destination: Total Science & S.P.Y - Piano Funk (Ft. Riya & DāM FunK) [320k]-SF8DGbfOFig.webm
[download] 100% of 5.57MiB in 00:03
[ffmpeg] Destination: Total Science & S.P.Y - Piano Funk (Ft. Riya & DāM FunK) [320k]-SF8DGbfOFig.mp3
Deleting original file Total Science & S.P.Y - Piano Funk (Ft. Riya & DāM FunK) [320k]-SF8DGbfOFig.webm (pass -k to keep)


  


  I then tried to convert the above command to an equivalent python script as follows :

  


  import youtube_dl
links = ["https://www.youtube.com/watch?v=SF8DGbfOFig&ab_channel=derang"]
ydl_args = {
        'audioformat': 'mp3',
        'outtmpl': '%(title)s.%(ext)s',
        'extractaudio': True
    }
with youtube_dl.YoutubeDL(ydl_args) as ydl:
    results = ydl.download(links)


  


  However, this does not succeed in generating an mp3 file of the audio. These are the logs I am getting :

  


  WARNING: Requested formats are incompatible for merge and will be merged into mkv.
[download] Destination: Total Science & S.P.Y - Piano Funk (Ft. Riya & DāM FunK) [320k].f135.mp4
[download] 100% of 4.42MiB in 00:02
[download] Destination: Total Science & S.P.Y - Piano Funk (Ft. Riya & DāM FunK) [320k].f251.webm
[download] 100% of 5.57MiB in 00:03
[ffmpeg] Merging formats into "Total Science & S.P.Y - Piano Funk (Ft. Riya & DāM FunK) [320k].mkv"
Deleting original file Total Science & S.P.Y - Piano Funk (Ft. Riya & DāM FunK) [320k].f135.mp4 (pass -k to keep)
Deleting original file Total Science & S.P.Y - Piano Funk (Ft. Riya & DāM FunK) [320k].f251.webm (pass -k to keep)


  


  What am I doing wrong here ? Aren't my command and python script equivalent ?

  


• Extracting a clip from a video with low fps

  1er juin 2016, par superMind

  I want to extract a clip from a video( downloaded from [1]) (which has low frame rate) by specifying the start and end time. In order to do that, I use the following command :

  ffmpeg -i example.webm -ss 116.38 -to 126.38 clip.mpg

  however, I get the following error :

  ---

  ffmpeg version N-80026-g936751b Copyright (c) 2000-2016 the FFmpeg developers
  
  built with gcc 4.8 (Ubuntu 4.8.4-2ubuntu1~14.04.3)
  
  configuration: --extra-libs=-ldl --prefix=/opt/ffmpeg --mandir=/usr/share/man --enable-avresample --disable-debug --enable-nonfree --enable-gpl --enable-version3 --enable-libopencore-amrnb --enable-libopencore-amrwb --disable-decoder=amrnb --disable-decoder=amrwb --enable-libpulse --enable-libfreetype --enable-gnutls --enable-libx264 --enable-libx265 --enable-libfdk-aac --enable-libvorbis --enable-libmp3lame --enable-libopus --enable-libvpx --enable-libspeex --enable-libass --enable-avisynth --enable-libsoxr --enable-libxvid --enable-libvidstab
  
  libavutil 55. 24.100 / 55. 24.100
  
  libavcodec 57. 42.100 / 57. 42.100
  
  libavformat 57. 36.100 / 57. 36.100
  
  libavdevice 57. 0.101 / 57. 0.101
  
  libavfilter 6. 45.100 / 6. 45.100
  
  libavresample 3. 0. 0 / 3. 0. 0
  
  libswscale 4. 1.100 / 4. 1.100
  
  libswresample 2. 0.101 / 2. 0.101
  
  libpostproc 54. 0.100 / 54. 0.100
  
  Input #0, matroska,webm, from 'example.webm':
  
  Metadata:
  
  encoder : Google
  
  Duration: 00:04:22.29, start: 0.000000, bitrate: 207 kb/s
  
  Stream #0:0: Video: vp8, yuv420p, 630x360, SAR 1:1 DAR 7:4, 6 fps, 6 tbr, 1k tbn (default)
  
  Stream #0:1: Audio: vorbis, 44100 Hz, stereo, fltp (default)
  
  [mpeg1video @ 0x252f200] MPEG1/2 does not support 5/1 fps
  
  Output #0, mpeg, to 'clip.mpg':
  
  Metadata:
  
  encoder : Google
  
  Stream #0:0: Unknown: none, SAR 1:1 DAR 0:0 (default)
  
  Metadata:
  
  encoder : Lavc57.42.100 mpeg1video
  
  Stream #0:1: Unknown: none (default)
  
  Metadata:
  
  encoder : Lavc57.42.100 mp2
  
  Stream mapping:
  
  Stream #0:0 -> #0:0 (vp8 (native) -> mpeg1video (native))
  
  Stream #0:1 -> #0:1 (vorbis (native) -> mp2 (native))
  
  Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height
  
  -----------------------------------------------------

  I tried by adding -r 20 to the above command. It works in this case but not sure this is correct way to do it.
  I was wondering how can I extract the clip from this video given start time and endtime ? what are parameters should I use ? or what is correct way to do it ?

  Thanks.

  [1]https://www.youtube.com/watch?v=Yc52pGHr0xc