Dashjs v3 - New Segments Management Model

[epiclabsDASH]

Description

It took long time and lot of back and forth but finally, with this PR, I am proposing the first set of big changes for dash.js v3.

As promised during the last face to face dash.js meeting in Berlin, this PR is coming with a re-architecture of the classes that are in charge of segments management so dash.js is less sensible to segment timing and/or alignment issues. We have been working in a much bigger change (fully rearchitecture dash.js core) during the last months but, given those are requiring more time than expected, what we have done is taking that big refactor and replacing just the parts of dash.js code base that we consider more sensible. That allows us to release faster and start getting feedback from you as soon as possible. We will incorporate all the other changes with a 1 month cadence, including all the fixes for the detected issues.

Most important changes coming in this PR:

• NextFragmentRequestRule. Code slightly changed, logic changed a lot. With the new approach NextFragmentRequestRule is less time dependant. Instead of starting to find the right segment to load by time, current approach leverages the fact that chunks are usually played sequentially. In other words, if the last segment we requested was Massive rearchitecture. #1, the next one should be Add feature detection for MediaSource support in reference player #2, the next one should be Initial commit of Media Source Extension tests. #3 and so on, (at least there was a seek operation in the middle).
• SegmentsGetter. These are not needed anymore. All segments requests are built "on the fly" taking into account the index of the segment requested or its time.
• DashHandler. Because its relation with SegmentsGetter and the mix of responsibilities that it has (using segmentsGetter, implement SegmentBase "type of segments" by itself, etc). We have simplify its code and its responsibilities.
• SegmentsController. We have added a new component, SegmentsController, whose responsibility is build segment objects given an index or time and that abstract the underlying segment method.
• SegmentBaseGetter. Added a new segment getter that implements the functionality behind managing segments that are defined in the manifest using SegmentBase method.

Please, I would like to ask you to test this PR as much as possible. I have uploaded it to http://dashjsv3.surge.sh/samples/index.html to make easier the testing phase. We are 200% dedicated to this so, please, feel free to report any issue you find. It is really important for me to get a fully stable version so I will be happy to work immediately on fixing any of your reported issues.

Pending work

• Working on unit tests for the new classes

Known issues:

• Under certain circumstances, for live streams using SegmentTimeline, we are not correctly calculating the DVRWindow of the stream. We are working on a fix for this.
• SegmentBase. We have detected a sporadic issue in SegmentBase streams when playing for a whil and after detecting the end of the stream. It is not easy to reproduce but we are working on it.
• Sometimes in multiperiod streams using SegmentTimeline, representation metrics are not correctly reported and top level application could get erroneous "current bitrate" value from dash.js. We are working on this.

[nicosang]

maybe add tests of representation and index parameters

[epiclabsDASH]

Yep, that's planned for this PR.

[nicosang]

maybe add tests of representation and requestedTime parameters