Media Source spec defines https://www.w3.org/TR/media-source/#sourcebuffer-coded-frame-processing > 1.3.1 Set timestampOffset equal to group start timestamp - presentation timestamp. The comment matches to the spec, but the code is different from the spec and the comment https://trac.webkit.org/browser/webkit/trunk/Source/WebCore/Modules/mediasource/SourceBuffer.cpp?rev=%09262766#L1485 > 1485 // 1.3.1 Set timestampOffset equal to group start timestamp - presentation timestamp. > 1486 m_timestampOffset = m_groupStartTimestamp; I couldn't create a content which reproduce this bug. Sorry.
<rdar://problem/96304755>
It is now correct: https://searchfox.org/wubkat/source/Source/WebCore/platform/graphics/SourceBufferPrivate.cpp#684 and Safari is passing all WPT tests as well: https://wpt.fyi/results/media-source/mediasource-timestamp-offset.html?label=master&label=experimental&aligned=&view=subtest&q=timestamp+offset
Thank you for the information!