[foms] Adaptive streaming

John Luther johnluther at webmproject.org
Fri Oct 29 08:13:08 PDT 2010

Wow, cool. I'd love to see a demo. 436K is a lot of data, you could do 30 or
40 seconds of mobile-rate video with that!


On Fri, Oct 29, 2010 at 10:43 AM, Jeroen Wijering
<jeroen at longtailvideo.com>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?
> Kind regards,
> Jeroen
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