Sometimes it doesn't - see bug 1099187. We end up with an ever-so-slightly wrong value for duration (based on bug 1065207) - but even in that case, we should make sure that the values at least match.
If this only appears in conjunction with bug 1065207, this may not affect mp4.
Component: Audio/Video → Audio/Video: Playback
I'm going to close this on the basis that bug 1099187 is closed.
Status: NEW → RESOLVED
Last Resolved: 3 years ago
Resolution: --- → WORKSFORME
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