Buffered ranges and seeking

Part of SABR in the extractor. The current PipePipeExtractor does not own a playback buffer or a YoutubeSabrStreamState; those policies live in the application layer that builds YoutubeSabrRequest objects.

What the extractor provides

YoutubeSabrRequest.Track can carry two pieces of caller-owned state:

• a YoutubeSabrFormatTimeline, parsed from initialization data;
• bufferedThrough, the last contiguous sequence the caller wants to report.

When both are present and bufferedThrough > 0, YoutubeSabrRequestHelper writes a bufferedRange starting at time zero and ending at the timeline end of that sequence. The range uses segment indexes starting at one and a timescale of 1000. If no timeline is available, no buffered range is emitted for that track.

This is intentionally conservative: a caller must not advertise a range past a hole. Reporting a later sequence while an earlier segment is missing can make the server skip the missing media and leave the reader stalled.

Seeking

For a seek, the application should derive a sequence with YoutubeSabrFormatTimeline.getSequenceAt(timeMs), discard or retain its own cached segments as appropriate, and build a new YoutubeSabrRequest.playback with the target player time and honest contiguous ranges. SABR itself does not provide a client cache API in the extractor.

The timeline lookup returns sequence 1 for non-positive times, the first entry whose end is after the requested time, or one past the final indexed sequence if the time is beyond the index. MP4 and WebM indexes are parsed from the format's initialization bytes; callers should wait for a valid timeline before claiming precise seek coverage.

Next: The session driver.