evazion 0e901b2f84 media file: get duration of animated GIFs, PNGs, and ugoiras. ...

Add methods to MediaFile to calculate the duration, frame count, and
frame rate of animated GIFs, PNGs, Ugoiras, and videos.

Some considerations:

* It's possible to have a GIF or PNG that's technically animated but
  just has one frame. These are treated as non-animated images.

* It's possible to have an animated GIF that has an unspecified
  frame rate. In this case we assume the frame rate is 10 FPS; this is
  browser dependent and may not be correct.

* Animated GIFs, PNGs, and Ugoiras all support variable frame rates.
  Technically, each frame has a separate delay, and the delays can be
  different frame-to-frame. We report only the average frame rate.

* Getting the duration of an APNG is surprisingly hard. Most tools don't
  have good support for APNGs since it's a rare and non-standardized
  format. The best we can do is get the frame count using ExifTool and the
  frame rate using ffprobe, then calculate the duration from that.

2021-09-27 05:18:25 -05:00

2.2 KiB

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