[Webkit-unassigned] [Bug 201323] New: [MSE] Don't enqueue samples that start at a big discontinuity

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=201323

            Bug ID: 201323
           Summary: [MSE] Don't enqueue samples that start at a big
                    discontinuity
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Media
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: aboya at igalia.com

With the old logic SourceBuffer was enqueueing the first frame to be
appended in any circumstances. This was a bug because the user could
append first [5, 10) and then [0, 5). With the old behavior [5, 10)
would be enqueued first despite being clearly ahead of the initial
playback time (zero). By the time [0, 5) is enqueued it can't be
enqueued anymore because the decodeQueue is already ahead.

This patch fixes that logic to work when the first segments are
appended unordered. The test media-source-first-append-not-starting-at-zero.html
validates it.

The test media-source-append-presentation-durations.html checks the
new logic does not break in presence of presentation duration !=
decode duration.

As part of the same logic block, the lastEnqueuedPresentationTime was
used to decide when it's necessary to perform reenqueue after an
.erase() (it is necessary if any enqueued frames are replaced). Using
lastEnqueuedPresentationTime was not entirely accurate in presence of
B-frames, as you could erase a frame that has a presentation time
higher than the last enqueued one. That logic is replaced with a
monotonicly increasing highestEnqueuedPresentationTime and is tested
by media-source-remove-b-frame.html.

Tests: media/media-source/media-source-append-presentation-durations.html
       media/media-source/media-source-first-append-not-starting-at-zero.html
       media/media-source/media-source-remove-b-frame.html

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