[
http://opencast.jira.com/browse/MH-9126?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=31644#comment-31644
]
Greg Logan commented on MH-9126:
--------------------------------
Keyframes are relative to the start of the file: The first frame for a
properly encoded file is, by definition, a keyframe. Keyframes come as an
interval (also called a group of pictures, or GOP). If you have a GOP size of
12, that means you have 1 keyframe, then 10 other frames, then another
keyframe.
As to finding a keyframe close enough, I suppose it depends on how our encoding
works. Looking at the trunk encoding definitions, the framerate can be as low
as 1 frame per second. We aren't setting the keyframe interval, but even if
it's low (say... 12, which is a default I found all over the place), we're
talking about every 12th *second* having a keyframe. I took a look at a demo
capture, and the screen is 5 fps with the camera being 15. Assuming that we
are basing our seek off of the screen capture, that's a keyframe every 2
seconds. Which explains why things are wonky: When you seek to a given point
it directs you to the nearest keyframe. If you are seeking 10 seconds forward,
and that's directly in between two keyframes you're going to have odd behaviour.
Disclaimer: My math may be wrong, as might the GOP interval. A GOP interval
of 12 is very very low, and lots of streaming tools use 250, so I would suspect
ours is much higher than my example.
> Trim UI: Player fast forward results in erratic jumps (7s, 8s, 10s)
> -------------------------------------------------------------------
>
> Key: MH-9126
> URL: http://opencast.jira.com/browse/MH-9126
> Project: Matterhorn Project
> Issue Type: Bug
> Components: Administrative Tools
> Affects Versions: 1.4
> Reporter: Olaf A. Schulte
> Assignee: Greg Logan
>
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators:
http://opencast.jira.com/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira
_______________________________________________
Matterhorn mailing list
[email protected]
http://lists.opencastproject.org/mailman/listinfo/matterhorn
To unsubscribe please email
[email protected]
_______________________________________________
