I wouldn't call these thumbnails "corrupted", there are some thumbnail compression artifacts though.

After downloading two media files, one with a "normal" thumbnail and one with a "corrupted" one, I have the same problem on my local computer (for the "corrupted" one, totem-video-thumbnailer does not create a thumbnail at all).

Is there a reason to assume that the software on the servers is faulty, instead of the video file?

Jan: Is there anything in this report that could be fixed on our side?

M8R-udfkkf wrote:

The videos play fine in Firefox 20 and VLC, so it appears to be a thumbnailer issue.

jgerber wrote:

This is a limitation/bug of libav/ffmpeg regarding ogg theora videos with large gaps between keyframes. We might be able to tune this but some videos will fail unless libav/ffmpeg is fixed to decode from the previous keyframe.

nils+bugzilla.wikimedia.org wrote:

Developer of the Open Access Media Importer here, the libav/ffmpeg situation is worse than you think. However, there are thumbnail solutions that work, like the Ogg Video Tools http://www.streamnik.de/oggvideotools.html.

More at https://github.com/erlehmann/open-access-media-importer/issues/105.

jgerber wrote:

One way to improve this would be to force more keyframes. currently TMH has a hard limit of how fare back it looks for the previous keyfr
ame.
Another option would be to switch Open Access Media Importer from Ogg (Theora/Vorbis) to WebM (VP8/Vorbis)

nils+bugzilla.wikimedia.org wrote:

Looking at the code, it already tries to use OggThumb. As I OggThumb does not produces garbage thumbnails, why not just install it?

https://git.wikimedia.org/blob/mediawiki%2Fextensions%2FTimedMediaHandler.git/83fc3186a3aabce5406814c29294f6bc2d90ca54/TimedMediaThumbnail.php

Change 86243 had a related patch set uploaded by J:
Fix thumbnails for low framerate Ogg Theora Videos

https://gerrit.wikimedia.org/r/86243

jgerber wrote:

OggThumb is no longer used since videos are accessed via http to extract frames and OggThumb does not support that.
Above patch calculates the seek offset based on framerate and fixes thumbnails for the videos linked above.

Change 86243 merged by Aaron Schulz:
Fix thumbnails for low framerate Ogg Theora Videos

https://gerrit.wikimedia.org/r/86243