Short video files fail to generate thumbnails

[glubsy]

Problem:

Video files with a duration shorter than 10 seconds fail to have their thumbnails generated by ffmpeg/avconv, as these programs are called with the argument -ss 0:00:10 (get the first frame after 10 seconds in). The ffmpeg output clearly states:

Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)

Solution:

Two possible implementations:

1. Iteration over the current way of doing things:
   • call ffmpeg/avconv with a hardcoded '0:00:10' first (what is currently being done)
   • capture the entire stderr output (not done properly currently, needs stderr redirection for capture, i.e. 2>&1),
   • look for a specific string to see if there is any error, i.e. nothing was encoded
   • if so, store the duration reported by ffmpeg's output into a $duration variable
   • call ffmpeg again with a new timestamp argument, which could be 10% of the duration, i.e. ($duration * 10) / 100;

2. A more thorough but perhaps slightly slower way:
   • call ffprobe/avprobe for every single video file encountered,
   • grab the duration reported by ffprobe into a $duration variable,
   • compute a timestamp at 10% of the duration, ie. $timestamp = ($duration * 10) / 100;
   • call ffmpeg with the resulting timestamp -ss $timestamp and let it generate the thumbnail

I would go with the latter implementation which seems better than a hard coded value of 10 seconds, which would force us to get every single ffmpeg output to parse and get potential error messages. A merge request is on the way.