On Wed, Feb 10, 2010 at 8:17 PM, Tim Starling <tstarling(a)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——