This PR will...

• Parse fmp4 truns to find audio and video base time and sample durations in one place
• Detect missing sync sample at start of fmp4 and error for switch or backtracking
• Use the same track for timestamp offsets with muxed mp4 (base initPTS on audio or video, whichever has the earliest sample times)
• Jump gaps in muxed audio video buffer on stall as long as the gap does not traverse more than one segment boundary
• Ensure that EoS is signaled only once the playhead is in the last buffered range

Why is this Pull Request needed?

Prevents decode errors cause by overlapping appends

Are there any points in the code the reviewer needs to double check?

Resolves issues:

#7114 (where pipeline error is a result of overlapping appends, not where platform decode error is unavoidable)

• Playback freezes when switching videos with same configuration #7114

Checklist

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• API or design changes are documented in API.md