This paves the way for SegmentTemplate and SegmentList based
mpds, which will implement DashSegmentIndex directly rather than
parsing an index from the media stream.
- Define DashSegmentIndex.
- Make use of DashSegmentIndex in chunk sources.
- Define an implementation of DashSegmentIndex that wraps a SegmentIndex.
- Add method that will allow Representations to return a DashSegmentIndex
directly in the future.
- Add support for non-contiguous index and initialization data in media streams.
For the Webm case this isn't enabled yet due to extractor limitations.
- Removed ability to fetch multiple chunks. This functionality does not extend
properly to SegmentList and SegmentTemplate variants of DASH.
Why: This was a bad initial choice. Manifests typically define bandwidth in
bits/sec. If you divide by 8 then you're throwing away information due to
rounding. Unfortunately it turns out that SegmentTemplate based manifests
require you to be able to recall the bitrate exactly (because it's substituted
in during segment URL construction).
Medium term: We should consider converting all our bandwidth estimation
over to bits/sec as well.
Note1: Also changed Period id to be a string, to match the mpd spec.
Note2: Made small optimization in FormatEvaluator to not consider discarding
the first chunk (durationBeforeThisSegmentUs will always be negative, and even
in the error case where it's not, removing the first thunk should be an error).
This can help custom ChunkSource implementations to act on
this information. For example an adaptive implementation may
choose to blacklist a problematic format if loads of that
format keep failing.
