[foms] What data is needed for adaptive stream switching?

Chris Pearce chris at pearce.org.nz
Tue Nov 23 13:24:30 PST 2010

Thanks for explaining Mark. Much appreciated.

On 24/11/2010 6:51 a.m., Mark Watson wrote:
> This is where there is scope for experimentation. What I think would be great is to define an API which can indicate these decision points, provide the two data sets (past incoming bandwidth) and (future bitrate of each stream) at some sufficient level of generality and indicate back the decision. Then we can experiment with more and less complex input data and more and less complex decision algorithms.

So in terms of what changes to browsers we'd need to make to start 
experimenting, we'd need to resurrect the @bufferedBytes attribute, add 
a @currentOffset attribute, and add some way for JS to access the 
RAP/keyframe index? Maybe we should add the @bufferedBytes data into 
@buffered, so you can easily map buffered time ranges to byte ranges? I 
guess these would have to be per-stream if we're playing multiple 
independent streams.

Or would you prefer an explicit download bandwidth and a per stream 
bitrate measure, calculated by the browser, over a specified time window?

In terms of an API which can indicate decision points, maybe an event 
which fires when playback enters a new chunk? Or fires when the download 
of a chunk finishes? Be aware we can't guarantee that any DOM events 
which we fire will arrive in a particularly timely manner, there could 
be any number of other things going on with the event queue.

Is there a direct mapping between a keyframe index and RAP points? What 
about audio streams in containers which don't index audio? Particularly 
in the case where we're playing multiple independent streams.

Chris P.

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