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• Detecting on which frame there is audio presence on a video

  26 août 2016, par drov

  I have a few video files that corresponds to a tv zapping (one channel with sound, then a black screen without sound, then sound again with the new channel)

  I already detect pretty much everything but I would like to know how long it takes for the audio to appear after the end of the black screen.

  Basically I extract the audio from the video and giving the starting frame I would like to know at which frame there is some audio again.

  Then using that I can easily calculate the time it took for the audio to appear.

• ffmpeg - Drawing rotated text on video with complex filters takes a very long time

  14 mai 2019, par Bedrule Paul

  I am trying to overlap different text pieces on some placeholders in a video, and I am using multiple complex filters of the following type :

  ffmpeg -i ~/Desktop/input.mp4 -filter_complex  \
  
      "color=black@0:100x100,format=yuva444p[c]; \
  
      [c][0]scale2ref[ct][mv31]; \
  
      [ct]setsar=1,split=1[t31];\
  
      [t31]\
  
      drawtext=text='text':x='main_w/2-text_w/2+70':y=210:fontsize="100":fontcolor=black,\
  
      drawtext=text='text2':x='main_w/2-text_w/2+75':y=340:fontsize="100":fontcolor=black,\
  
      rotate=-0.07:ow=rotw(-0.07):oh=roth(-0.07):c=black@0[txta31]; \
  
      [mv31][txta31]overlay=enable='between(t, 0, 1.15)':x='min(0,-H*sin(-0.07))':y='min(0,W*sin(-0.07))':shortest=1" \
  
         ~/Desktop/result.mp4 -y1

  My goal is to write differently rotated texts on different time intervals in the video. The problem is that at about 10-12 [t31]-like pieces(here is an example of only one command), the rendering time of the video is twice the time of the video, whereas drawing straight horizontal text takes about 10-20% of the total video length (examples, for a 1 minute video, it takes about 8-10 seconds to write straight horizontal text, and about 2 minutes to write the same amount of text, but inclined with an angle). Is there any better way to do these multiple rotated text bits with more performance ?

• `FFmpeg` `segment_time` inserts blank frames at the beginning of segment

  27 août 2017, par asdf

  I am using the following command to cut videos in parts.
  I need parts to be less than passed max_length param, I do not need precise cuts.

  ffmpeg -i input.mov \
  
  -segment_time 20 -f segment -reset_timestamps 1 input_%d.mov

  Every first part video file cut by ffmpeg is not 20s, but 20.5s long. And it has several black frames at the beginning inserted by ffmpeg.

  I don’t mind having 19.5s long parts if that is needed because of keyframes. But I need to get rid of those black frames at the beginning so that videos cut in parts could be concatenated in a single video later without any troubles.

  Could you give me an advice ?

  ---

  Upd :

  There were no black frames in an original video which was 23 seconds long.
  I made a cut setting 12 as a segment length.

  I also had to add -c copy because I would like to keep original quality if that’s possible.

  Leading black frames were added after a cut to part 1 which is 12 seconds long.

  Trailing black frames were added after a cut to part 2 which is 10 seconds long.

  https://www.dropbox.com/sh/zo8evta3w1xho3o/AABpTB3w3CuPa1WcghkSIVfna?dl=0

  The command used was

  ffmpeg -y -i /Users/nt/Desktop/cut/AAL_CrSlowMo_041413_1.mov -c copy -segment_time 12 -f segment -reset_timestamps 1 /Users/nt/Desktop/cut/AAL_CrSlowMo_041413_1_%d.mov

  Here’s output of ffmpeg :
  https://gist.github.com/nmtitov/ad102539f95fa03b95f10a46f8d99663