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• 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

• lavfi/vf_libplacebo : simplify SAR normalization

  20 juin 2023, par Niklas Haas

  lavfi/vf_libplacebo : simplify SAR normalization
  The old logic was trying to be excessively clever in "deducing" that the
  
  user wanted to stretch/scale the image when ow/oh differed from iw/ih
  
  aspect ratio. But this is almost surely unintended except in
  
  pathological cases, and in those cases users should simply disable
  
  normalize_sar and do all the stretching/scaling logic themselves. This
  
  is especially important in multi-input mode, where the canvas may be
  
  vastly different from the input dimensions of any stream. Also, passing
  
  through input 0 SAR in multi-input mode is arbitrary and nearly useless,
  
  so again force output SAR to 1:1 here.
  

  • [DH] libavfilter/vf_libplacebo.c

• hwcontext_vulkan : require storage properties to claim formats as supported

  24 novembre 2024, par Lynne

  hwcontext_vulkan : require storage properties to claim formats as supported
  This function dates back a long time ago, before vkfmt_from_pixfmt2.
  
  When it was converted over, the thought was that this was far too
  
  restrictive to demand storage images for each format.
  
  With the new clever function, it makes sure to check that the compatible
  
  subformats a format can be used as support storage capabilities.
  This gets rid of fake support for RGB48/RGB96 which some implementations
  
  offer but don't support using as storage images.
  

  • [DH] libavutil/hwcontext_vulkan.c