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• How do I reverse a video in ffmpeg ?

  19 avril 2023, par Will Beeson

  - Full Error :

  


  Stream specifier 's1:v' in filtergraph description [0]split=2:outputs=2[s0][s1] ;[s1:v]reverse[s2] ;[s0][s2]concat=a=0:n=2:v=1[s3] matches no streams.

  


  - Formatted Error

  


  

  • [0]split=2:outputs=2[s0][s1] ;

  


  • [s1:v]reverse[s2] ;

  


  • [s0][s2]concat=a=0:n=2:v=1[s3]

  


  


  - Code :

  


  instances = (
    ffmpeg
    .input(self.video_file)
    .filter_multi_output(filter_name="split", outputs=2)
)
ordered_edits = []
for i in range(2):
    if i%2 == 0:
        ordered_edits.append(
            instances[i]
        )
    else:
        ordered_edits.append(
            instances[i].video.filter(filter_name="reverse")
        )
(
    ffmpeg
    .concat(*ordered_edits, a=0, v=1)
    .output('done/output.mp4')
    .run(overwrite_output=True))


  


  Looking at the error code, it seems like s1:v should be a valid reference. The only thing I can think of is that there is an issue saving an exclusive video input into a nonspecified output. The files don't actually have any audio, I just want the video.

  


  I'm lost, please help ffmpeg experts of the world !

  


• avformat/matroskaenc : Simplify writing Cues

  30 décembre 2019, par Andreas Rheinhardt

  avformat/matroskaenc : Simplify writing Cues
  When the Matroska muxer writes the Cues (the index), it groups index
  
  entries with the same timestamp into the same CuePoint to save space.
  
  But given Matroska's variable-length length fields, it either needs
  
  to have an upper bound of the final size of the CuePoint before writing it
  
  or the CuePoint has to be assembled in a different buffer, so that after
  
  having assembled the CuePoint (when the real size is known), the CuePoint's
  
  header can be written and its data copied after it.
  The first of these approaches is the currently used one. This entails
  
  finding out the number of entries in a CuePoint before starting the
  
  CuePoint and therefore means that the list is read at least twice.
  
  Furthermore, a worst-case upper-bound for the length of a single entry
  
  was used, so that sometimes bytes are wasted on length fields.
  This commit switches to the second approach. This is no longer more
  
  expensive than the current approach if one only resets the dynamic
  
  buffer used to write the CuePoint's content instead of opening a new
  
  buffer for every CuePoint : Writing the trailer of a file with 540.000
  
  CuePoints improved actually from 219054414 decicycles to 2164379394
  
  decicycles (based upon 50 iterations).
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/matroskaenc.c

• Adding a text overlay with constant size to a video with varying resolutions using ffmpeg

  22 décembre 2020, par BetaLixT

  I have a video with different resolutions at different points of the video and need to add a text overlay to it. I'm new with ffmpeg, the following is one of the commands I've tried

  


  ffmpeg -i input.mp4 -vf "drawtext=text='Hello World'" -c:a copy output.mp4


  


  But the output has blurry text with it resizing every few seconds (I'm guessing because of the various resolutions in the video) and some parts of the video have their aspect ratios altered.

  


  Information on input file

  


  The input.mp4 video is generated from some .h264 raw data converted to mp4 and some blank mp4 generated that are all concatenated together, following are the commands

  


  h264 to mp4 :

  


  ffmpeg a.h264 -c copy a.mp4


  


  blank mp4

  


  ffmpeg -t 5 -f lavfi -i color=c=black:s=200x200 -c:v libx264 -tune stillimage -pix_fmt yuv420p -video_track_timescale 1200000 b.mp4


  


  Concat :

  


  ffmpeg -safe 0 -f concat -i list.txt -s 720x960 -c copy input.mp4


  


  I'd be thankful for any advice on how I could achieve this