[foms] Adaptive streaming

[Silvia Pfeiffer]

On Sat, Oct 30, 2010 at 7:17 AM, Mark Watson <watsonm at netflix.com> wrote:
>
> On Oct 29, 2010, at 7:43 AM, Jeroen Wijering wrote:
>
>>
>> On Oct 27, 2010, at 5:51 PM, Mark Watson wrote:
>>
>>>> Do files with a compacted index still play on devices that do not expect it? Think current mobile phones.
>>>
>>> In DASH its just a fragmented MP4 file with an extra box ("Segment Index") near the beginning. Existing players would ignore the new box.
>>
>> Do you have an example video? I'm curious to see one and do a few tests.
>>
>>
>>>> If WebM / Ogg by its nature already has much smaller headers, one of the big drawbacks of range-request streaming would not be valid for these containers.
>>>
>>> I need to read up on the WebM format (bit of a confession, being on this list, sorry!). But I understood you have the framing information with the samples and therefore smaller headers and probably no need for any kind of formal fragmentation. So your "fragment" would just be a notional concept of a group of samples spanning some time period. Your index would provide time and byte offsets for these fragments. If you already have something which provides time and byte offsets for Random Access Points (for seeking) you could probably re-use that. (Re-using Movie Fragment Random Access box in mp4 was discussed instead of creating the new Segment Index. Segment Index was chosen for some slightly obscure technical reasons).
>>
>> Just did a quick test with a 15-minute WebM video (keyframes 2-6s):
>>
>> http://content.bitsontherun.com/videos/a95zAVN1-710492.webm
>>
>> The first Clusterheader appeared at 44k.
>>
>> That's pretty nice compared to an MP4 conversion with the same keyframe interval, where the MOOV box is 480k:
>>
>> http://content.bitsontherun.com/videos/a95zAVN1-600332.mp4
>>
>> So it looks like my concern with range requests (startup delays due to big headers) is not valid for WebM files....
>>
>> ----
>>
>> If the videoElement would expose a callback with valid range-requests to javascript, the scripting layer would be aware of the valid ranges in a quality level. For example something like "onSeekpoints" that returns:
>>
>> [
>> {position: 0,000,start: 8839, end:9957},
>> {position: 1,287,start: 9957, end:10994},
>> {position: 3,071,start: 10995, end:19840}
>> ]
>>
>> Next, this info can be used to do adaptive streaming using the appendVideo function:
>>
>> videoElement.appendVideo("http://example.com/video_800.webm", 8839, 9957);
>>
>> With this, plús some way to retrieve the bandwidth / bytesLoaded, it should be possible to build a fully functional WebM adaptive streaming demo in javascript - using existing WebM files.
>>
>> Would this work? Are there oversights? What do the FOMS browser developers think of such a first step?
>
> The one additional thing I think is needed is that you need also to give the player the file headers for each variant (Header/Segment/Track for WebM, Movie Header and Segment Index for DASH mp4). Maybe also the Cueing Data in WebM can be used as an index ?
>
> There are various ways to do this and those more expert in HTML5 than me can suggest the best, but one way might be:
>
> tag = videoElement.initializeVideo( "http://example.com/video_800.webm" )
>
> then onSeekpoints returns { tag: 1, seekpoints = [ { position: 0, start: 8839, end: 9957 }, ... ] }


If we are considering adding an onSeekpoints() function to the
JavaScript API of <video>, how large do we think such a table can be?
Is this just supposed to return the seek table that is at the
beginning of the file - such as the recently newly introduced
OggIndex[1]? I think that has a somewhat limited size, so that's
probably acceptable. What about WebM and MPEG - do they have such a
seek table with a max size?

[1] http://github.com/cpearce/OggIndex/blob/master/Skeleton-4.0-Index-Specification.txt

Cheers,
Silvia.



> then videoElement.appendVideo( tag, "http://example.com/video_800.webm", 8839, 9957 )
>
> You are still appending to a single common playout buffer, the tag is about where the information comes from, or rather how to understand it, not where it is appended to.
>
> Same, independently, for audio.
>
> ...Mark
>
>
>>
>> Kind regards,
>>
>> Jeroen
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