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• Input seeking for frame at specified timestamp with Py-AV

  9 décembre 2019, par neonScarecrow

  I have a project already using Py-AV and am trying to replicate a specific ffmpeg command. The goal is to get a frame roughly around the specified timestamp.

  Here’s the ffmpeg commmand :
  https://trac.ffmpeg.org/wiki/Seeking

  ffmpeg -ss 14 -i https://some_url.mp4 -frames:v 1 frame_at_14_seconds.jpg

  Here’s my code :

      #return one frame around 14 seconds into the movie
  
      target_sec = 14 
  
      container = av.open('https://some_url.mp4', 'r')
  
      container.streams.video[0].thread_type = 'AUTO'
  
      video_stream = next(s for s in container.streams if s.type == 'video')
  
      time_base = float(video_stream.time_base)
  
      target_timestamp = int(target_sec / time_base) + video_stream.start_time
  
      video_stream.seek(target_timestamp)
  
      for frame in container.decode(video_stream):
  
          frame.to_image().save('frame_at_14_seconds.jpg')
  
          break

  Additionally, I have found any documentation about this, but does anyone know if either command (ffmpeg/av.open) is downloading the entire file to a tmp file behind the scenes. I’m looking for a less memory-intensive way to read a frame for every second in an up to 60 second video.

• avformat/matroskaenc : Allow to use custom reformatting functions

  15 janvier 2022, par Andreas Rheinhardt

  avformat/matroskaenc : Allow to use custom reformatting functions
  Matroska uses variable-length elements and in order not to waste
  
  bytes on length fields, the length of the data to write needs to
  
  be known before writing the length field. Annex B H.264/5 and
  
  WavPack need to be reformatted to know this length and this
  
  currently involves writing the data into temporary buffers ;
  
  AV1 sometimes suffers from this as well.
  This commit aims to solve this by adding a callback that is called
  
  twice per packet : Once to get the size and once to actually write
  
  the data. In case of WavPack and AV1 (where parsing is cheap due
  
  to length fields) both calls will just parse the data with only
  
  the second function writing anything. For H.264/5, the position
  
  of the NALUs will need to be stored to be written lateron.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavformat/matroskaenc.c

• FFmpeg Drawbox Errors ?

  12 mars 2021, par Alex Gurr

  Using ffmpeg version 4.3.2.

  


  Command :

  


  ffmpeg -y

  -i /usr/src/app/backgrounds/pink-blue.jpg
  -i files/fuzzy-octopus-5/path/file.webm
  -i files/fuzzy-octopus-5/path/file.webm
  -i /usr/src/app/logo.png
  -filter_complex "
    [0]drawbox=x=-140:y=(((H-th)/2) - 205):w=840:h=490:color=white@0.2:t=fill,
       drawbox=x=770:y=(((H-th)/2) - 205):w=840:h=490:color=white@0.2:t=fill[bg]; 
    ...


  


  However I am getting the following errors ?

  


  Error while processing the decoded data for stream #3:0
Failed to inject frame into filter network: Invalid argument
Error reinitializing filters!
[Parsed_drawbox_0 @ 0x564a87058e80] Failed to configure input pad on Parsed_drawbox_0
[Parsed_drawbox_0 @ 0x564a87058e80] Error when evaluating the expression '(((H-th)/2) - 205)'.
Last message repeated 5 times
[Parsed_drawbox_0 @ 0x564a87058e80] [Eval @ 0x7ffcf25dc650] Undefined constant or missing '(' in 'H-th)/2)-205)'


  


  I have the right amount of brackets and this definitely works on my local machine (macOS). It's only throwing this error in our deployed AWS EC2 linux instance.

  


  Any ideas ? Thanks !

  


  Update : Tried replacing th with h but get the same error