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• Evaluate function within ffmpeg drawtext

  22 juin 2022, par Dan Steingart

  I am looking to display a counter that is a multiple of the frame number on a video created with ffmpeg. Previous answers on SO taught me that a command of the form

  


  ffmpeg -y -r 25  -pattern_type glob -i '*.jpg' -vf "text='%{n}': start_number=0: x=0: y=0: fontcolor=black: fontsize=30: box=1: boxcolor=white: boxborderw=5" -c:a copy movie.mp4


  


  Will display the frame number, and this works nicely. But if I try to evaluate an expression within the %{}, e.g.

  


  ffmpeg -y -r 25  -pattern_type glob -i '*.jpg' -vf "text='%{n*50}': start_number=0: x=0: y=0: fontcolor=black: fontsize=30: box=1: boxcolor=white: boxborderw=5" -c:a copy movie.mp4


  


  Then I get the following error

  


  [Parsed_drawtext_0 @ 0x55683f9b00] %{n*50} is not known    


  


  on each frame. What is the proper syntax to evaluate n*50 and display in drawtext ? TIA.

  


• ffmpeg : Dynamically set output duration based on sliding text width

  18 janvier 2016, par John Whiteman

  I need to create a smooth ’news ticker’ on a low powered android device. Unfortunately this is impossible at runtime using HTML or native code as there is always some stutter or glitch.

  I’ve created a solution that gives me a smooth result by encoding an mp4 for each message and displaying one video after the other. This is the code I’m using :

  ffmpeg -f lavfi -i color=c=black:s=1280x100 -vf "drawtext=BebasNeue.otf:fontsize=60:fontcolor=white:y=h-line_h-30:x=-(4*n)+1280:text='Hello world'" -t 10 output.mp4

  Problem :
  I need to set the video’s duration dynamically so that the video stops when the text has completed it’s journey from right to left. The messages will be of varying lengths and I need each message to scroll at a constant speed (ie. an mp4 with a longer message would have a longer duration).

  Is this possible via an expression ? If not is there some clever way I can calculate this outside of ffmpeg and pass it to the ’-t’ (duration) parameter ?

  ** Edit **
  To calculate outside of ffmpeg I can do a calculation like video_width + text_width / video_fps (ie. 1280 + 262 / 25) to give me the duration. So now I’m just looking to see if this is possible within the ffmpeg command line itself. t

  Many thanks

• How can I create time gaps in video recordings using newest version of FFMPEG ?

  10 juin 2019, par Jovana Kostić

  I am new to the forum so I hope I’ve formulated this question correctly.

  I have downloaded newest version of FFMPEG and I would like to use it to modify existing video by inserting time gaps in it.

  Here is what I mean by time gap. If I have input video that lasts 2 seconds and was recorded at FPS=10, timestamps of its frames would be as follows :

  0.1s, 0.2s,0.3s,0.4s, .. 1.7s, 1.8s, 1.9.s, 2s

  If I would to introduce time gaps, input videos frame would be something like this :

  0.1s, 0.2s, 0.9s, 1s, 1.1s, 1.7s, 1.8s, 1.9s, 2s

  Is something like this possible to achieve ?

   !!!EDIT !!!

  I would like to post here results of the commands Gyan was kind enough to comment.

  For command :

  ffmpeg -i input.mp4 -vf "setpts='PTS+gte(t,0.3)*(0.6/TB)+gte(t,1.5)*(1.1/TB)',showinfo" -vsync vfr out.mp4

  I am getting :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'input.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf58.20.100
  
    Duration: 00:00:09.30, start: 0.000000, bitrate: 1185 kb/s
  
      Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 960x540, 1184 kb/s, 10 fps, 10 tbr, 10240 tbn, 20480 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler
  
  File 'out.mp4' already exists. Overwrite ? [y/N] y
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
  
  Press [q] to stop, [?] for help
  
  [Parsed_setpts_0 @ 0x55e4f4f85400] [Eval @ 0x7fffadb2ac80] Unknown function in 't,0.3)*(0.6/TB)+gte(t,1.5)*(1.1/TB)'
  
  [Parsed_setpts_0 @ 0x55e4f4f85400] Error while parsing expression 'PTS+gte(t,0.3)*(0.6/TB)+gte(t,1.5)*(1.1/TB)'
  
  [AVFilterGraph @ 0x55e4f4eff400] Error initializing filter 'setpts' with args 'PTS+gte(t,0.3)*(0.6/TB)+gte(t,1.5)*(1.1/TB)'
  
  Error reinitializing filters!
  
  Failed to inject frame into filter network: Invalid argument
  
  Error while processing the decoded data for stream #0:0
  
  Conversion failed!

  And for command :

  ffmpeg -i input.mp4 -vf select='not(between(t,0.3,0.7)+between(t,1.5.1.8))' -vsync vfr out.mp4

  I am getting :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'input.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf58.20.100
  
    Duration: 00:00:09.30, start: 0.000000, bitrate: 1185 kb/s
  
      Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 960x540, 1184 kb/s, 10 fps, 10 tbr, 10240 tbn, 20480 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler
  
  File 'out.mp4' already exists. Overwrite ? [y/N] y
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
  
  Press [q] to stop, [?] for help
  
  [Parsed_select_0 @ 0x55ce2c4f9d00] [Eval @ 0x7ffc980730c0] Missing ')' or too many args in 'between(t'
  
  [Parsed_select_0 @ 0x55ce2c4f9d00] Error while parsing expression 'not(between(t'
  
  [AVFilterGraph @ 0x55ce2c491a00] Error initializing filter 'select' with args 'not(between(t'
  
  Error reinitializing filters!
  
  Failed to inject frame into filter network: Invalid argument
  
  Error while processing the decoded data for stream #0:0
  
  Conversion failed!