On Wed, Feb 10, 2010 at 8:17 PM, Tim Starling tstarling@wikimedia.org wrote:
Obviously if there is some encoder that, with the default settings, is generating 10 second files with a single keyframe and 240 inter frames, and this encoder is significant for Wikimedia, then I will have to rethink this approach.
256-frame keyframe interval is the default for anything libtheora 1.1 based in two-pass mode... So, yes. I'm pretty sure thats relevant.
I wouldn't have even realized the existing processing chain was failing on files that contained no keyframes past the midpoint were it not for the fact that I'd bumped into failed thumbnailing on short files. ::shrugs::
There isn't really a reasonable "fixed heuristic distance between keyframes", the encoder can put them anywhere subject to the limitation that they not be more than KEYINT away from the last one. So even knowing the interval the locations can't be reliably determined without scanning the file.
The alternative "one line fix" is switching to a thumbnailer that actually thumbnails the requested location. All the better when the thumbnailer correctly handles 4:2:2 and 4:4:4 colorspaces. Just saying——