Bug 138820 – Timeupdate fires during a buffer under-run.

• Component: Media
• Status: NEW

[Jamie Stackhouse]

Created attachment 241760 [details]
Screenshot showcasing odd timeupdate.

Test URL: http://www.w3.org/2010/05/video/mediaevents.html, and http://www.videojs.com.

Step to reproduce:
1: Throttle internet connection to an appropriate level that will cause the buffer to run out.
2: Play video

Expected Results:
1: Plays until there is not buffer to draw upon to render new frames.
2: MediaElement runs out of data, and the readyState changes from 3 -> 2 -> 1.
3: MediaElement emits "waiting".
4: Buffering occurs...
5: MediaElement readyState changes from 1 -> 2 -> 3.
6: MediaElement emits "playing".
7: MediaElement plays..
8: Occasional "timeupdate" events during playback.

Actual Results:
1: Plays until no buffer.
2: Waiting event is sometimes fired, but not always between buffers.
3: Ready state is not changing from 3 when there is no playback.
4: The currentTime continues to update as if playback was occuring. Occassionally it "fixes" itself and loops back to the real currentTime.
5: Playback begins again.

However, if user has a long buffer period. It is possible to end a video by playing and pausing the video via the controls. It appears to be the cause of the MediaController attribute.

The videojs.com link is a open source library exhibiting the symptoms of this issue, where a user who encounters a buffer under-run are shown no feedback, and their play progress or "scrubber" advances, and then shoots back. VideoJS does not make use of MediaControllers at this point in core.

[Jamie Stackhouse]

"VideoJS does not make use of MediaControllers at this point in core."
MediaControllers are not used, to my knowledege.

[Radar WebKit Bug Importer]

<rdar://problem/21965808>

Hi, 
I also experience this issue. No other browser has this problem. At first currentTime reporting is increasing even though video is not playing then after real time is obtained it is rewinded back, which makes it impossible to accurately present playback time. I made a simple reproduction html page: https://stackblitz.com/edit/stackblitz-starters-drhjyvj8?file=index.html. But the discrepancies vary depending on browser load and video, sometimes reaching over 0.3s, which is definitely noticeable.

I also found a related bug here https://bugs.webkit.org/show_bug.cgi?id=287430.

Please fix this, as it makes safari unusable for precise time-oriented video playback.