[Webkit-unassigned] [Bug 177483] New: Appending media to the start of a buffer range drops buffer after the append.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=177483

            Bug ID: 177483
           Summary: Appending media to the start of a buffer range drops
                    buffer after the append.
           Product: WebKit
           Version: Safari 10
          Hardware: Macintosh
                OS: macOS 10.12
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Media Elements
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: robert.bryer at bbc.co.uk

When appending media to the start of a buffered range, webkit will remove a portion of buffer after the append, keeping the buffer as two separate ranges.

To reproduce:
http://reference.dashif.org/dash.js/v2.6.0/samples/dash-if-reference-player/index.html

1. Click load.
2. Seek forward to a time like 3:00, await some buffer at this time.
3. Seek back to 2:45, play until 3:00.
4. Observe that there is a gap in the buffer at the first segment downloaded(between 176 and 178).

When appending the segment again to fill the gap, a new gap appears at the next segment boundary, and so on - effectively meaning we need to replace all the buffered media from 3:00 onwards.

The fact that the above example doesn't play out is our fault(we should be checking .buffered when deciding what to fetch, and we have a fix already for this so we can make it play). But we probably shouldn't need to replace all the buffer ahead after seeking backwards. What's going on here?

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