[whatwg] Extending HTML 5 video for adaptive streaming

Robert O'Callahan robert at ocallahan.org
Thu Jun 30 16:13:25 PDT 2011

On Fri, Jul 1, 2011 at 4:59 AM, Aaron Colwell <acolwell at google.com> wrote:

> I've also been looking at the WebRTC MediaStream API and was wondering if
> it
> makes more sense to create an object similar to the LocalMediaStream
> object.
> This has the benefits of unifying how media streams are handled independent
> of whether they come from a camera or a JavaScript based streaming
> algorithm. This could also enable sending the media stream through a
> Peer-to-peer connection instead of only allowing a camera as a source. Here
> is an example of the type of object I'm talking about.

I think MediaStreams should not be dealing with compressed data except as an
optimization when access to decoded data is not required anywhere in the
stream pipeline. If you want to do processing of decoded stream data (which
I do --- see
then introducing a decoder inside the stream processing graph creates all
sorts of complications.

I think the natural way to support the functionality you're looking for is
to extend the concept of Blob URLs. Right now you can create a binary Blob,
mint a URL for it and set that URL as the source for a media element. The
only extension you need is the ability to append data to the Blob while
retaining the same URL; you would need to initially mark the Blob as "open"
to indicate to URL consumers that the data stream has not ended. That
extension would be useful for all sorts of things because you can use those
Blob URLs anywhere. An alternative would be to create a new kind of object
representing an appendable sequence of Blobs and create an API to mint URLs
for it.

Note that with my API proposal above, you can get a MediaStream from a media
element that's using any URL and send that through a PeerConnection.

"If we claim to be without sin, we deceive ourselves and the truth is not in
us. If we confess our sins, he is faithful and just and will forgive us our
sins and purify us from all unrighteousness. If we claim we have not sinned,
we make him out to be a liar and his word is not in us." [1 John 1:8-10]

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