GNOME Bugzilla – Bug 619374
webmmux: files created not fully valid, first video block in cluster must be keyframe
Last modified: 2018-05-01 09:42:51 UTC
encoding webm files with gstreamer, the resulting files does not fully validate with mkvalidator(from svn) here the error: ERR201: Invalid Tag for profile 'webm v2' at 7605134 in Tags while this is valid in matroska its not part of the webm subset.
What's the tag that is written at this position?
Ah, I see. Yes, webm doesn't allow tags and writing of tags should be disabled for webmmux.
But OTOH the webm container spec says only which things are supported, everything else is "undecided" but not "unsupported/forbidden". http://www.webmproject.org/code/specs/container/
undecided is a strange state, mkvalidator right now treats those as errors, but you are right, it might not be an issue as long as the feature is not related to playback, like tags
just checked with the latest mkvalidator from svn it adds some more conformance tests. i get a lot of those errors now: MWRN0C0: First Block for video track #1 in Cluster at 58824 is not a keyframe
(In reply to comment #4) > undecided is a strange state mkvalidator right now treats those as errors, > but you are right, it might not be an issue as long as the feature is not related to playback, like tags How are tags related to playback? Ignore them and everything still works as expected ;) (In reply to comment #5) > just checked with the latest mkvalidator from svn > it adds some more conformance tests. > i get a lot of those errors now: > MWRN0C0: First Block for video track #1 in Cluster at 58824 is not a keyframe Hrm, yes. That's a real problem now. I'll work on this. Currently the muxers starts a new cluster after 2 seconds (IIRC) or when a keyframe appears. For webm it should only do the latter. But from the webm spec it's only a "should", no "must".
Yes, we should fix this. However, according to http://www.webmproject.org/code/specs/container/#muxer_guidelines this is only a "SHOULD" and not a "MUST" so should not result in an 'error' in mkvalidator IMHO, but at best a warning or info.
(In reply to comment #5) > just checked with the latest mkvalidator from svn > it adds some more conformance tests. > i get a lot of those errors now: > MWRN0C0: First Block for video track #1 in Cluster at 58824 is not a keyframe This message is just a warning. If you want to validate a file against real errors you can use --no-warn.
(In reply to comment #6) > Currently the muxers starts a new cluster after 2 seconds (IIRC) or when a > keyframe appears. For webm it should only do the latter. But from the webm spec > it's only a "should", no "must". But they also say: "Muxers should treat all guidelines marked should in this section as must" A little bit confusing :)
No activity in 8 years. Not an issue.