[MSE] Skip initial buffering rate computation

[eocanha]

1581c8a

[MSE] Skip initial buffering rate computation
https://bugs.webkit.org/show_bug.cgi?id=253074

Reviewed by Jer Noble.

m_timeOfBufferingMonitor is initialized in SourceBuffer at creation
time. If the first call to monitorBufferingRate() takes too much to
happen for whatever reason (eg: because the webpage takes too much to
perform the first append), the computed interval is already going to be
too big and generate an artificially low m_averageBufferRate.

To mitigate this, I've added code to initialize m_timeOfBufferingMonitor
to zero, detect that special value in monitorBufferingRate() and skip
the first time that the rate computation is done (just assigning the
"now" time to m_timeOfBufferingMonitor, so when the next update is done,
the interval is most realistic).

However, since monitorBufferingRate() calls are only done from
canPlayThroughRange() and that call might happen only once in some
layout tests and production scenarios, m_averageBufferRate might not
reach accurate values on time and make the test fail. To mitigate that,
I've also added extra calls every time a buffer is appended and every
time the append completes.

See: WebPlatformForEmbedded/WPEWebKit#928 (comment)

* Source/WebCore/Modules/mediasource/SourceBuffer.cpp: Initialize m_timeOfBufferingMonitor to zero, meaning "never updated before".
(WebCore::SourceBuffer::appendBuffer): Update monitorBufferingRate.
(WebCore::SourceBuffer::sourceBufferPrivateAppendComplete): UpdateMonitorBufferingRate.
(WebCore::SourceBuffer::monitorBufferingRate): Skip first m_averageBufferRate update.

Canonical link: https://commits.webkit.org/261328@main

b16b73b

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🛠 gtk
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🧪 gtk-wk2
	✅ 🛠 tv	✅ 🧪 mac-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv-sim	✅ 🧪 mac-AS-debug-wk2
	✅ 🛠 watch	✅ 🧪 mac-wk2-stress
✅ 🛠 🧪 merge	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on previous version of this PR (hash 2026e03)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🛠 gtk
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	❌ 🧪 gtk-wk2
	✅ 🧪 api-ios	❌ 🧪 mac-wk1	❌ 🧪 api-gtk
	✅ 🛠 tv	❌ 🧪 mac-wk2
	✅ 🛠 tv-sim	❌ 🧪 mac-AS-debug-wk2
	✅ 🛠 watch	✅ 🧪 mac-wk2-stress
	✅ 🛠 watch-sim

[eocanha]

The patch as it is is causing 3 regressions in glib platforms:

• media/media-source/media-source-canplaythrough-event.html
• media/media-source/media-source-video-renders.html
• media/media-source/media-source-webm-append-buffer-after-abort.html

I'm going to have a quick look into them before considering merging the patch.

[philn]

Seems to break tests on mac ports too.

[webkit-early-warning-system]

EWS run on current version of this PR (hash b16b73b)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🛠 gtk
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🧪 gtk-wk2
	✅ 🛠 tv	✅ 🧪 mac-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv-sim	✅ 🧪 mac-AS-debug-wk2
	✅ 🛠 watch	✅ 🧪 mac-wk2-stress
✅ 🛠 🧪 merge	✅ 🛠 watch-sim

[eocanha]

The problem seemed to be that just one call to monitorBufferingRate() before the test checks canplaythrough isn't enough to get the new mechanism working (2 calls at minimum are needed). I've added extra calls every time an append is done and everytime an append is completed. That solved the issues on WebKitGTK. Let's see if it solves them too for Apple ports.

[eocanha]

@jernoble, if you confirm that you don't see anything wrong about calling monitorBufferingRate() from SourceBuffer::appendBuffer() and SourceBuffer::sourceBufferPrivateAppendComplete() to force a more frequent update of m_averageBufferRate, I can merge the patch. All the tests are passing now.

[eocanha]

@jernoble, in case there's no complain from your side in some days, I'll merge this PR next week.

[webkit-commit-queue]

Committed 261328@main (1581c8a): https://commits.webkit.org/261328@main

Reviewed commits have been landed. Closing PR #10793 and removing active labels.