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Re: Semantics question for onaddstream() callback

From: Justin Uberti <juberti@google.com>
Date: Sun, 13 Nov 2011 11:35:04 -0500
Message-ID: <CAOJ7v-3Bioe0O1uXPRD9-VwXXoR+UQunoO+-1T4sPTBOEMm=Dg@mail.gmail.com>
To: Stefan Håkansson <stefan.lk.hakansson@ericsson.com>
Cc: Eric Rescorla <ekr@rtfm.com>, Harald Alvestrand <harald@alvestrand.no>, "public-webrtc@w3.org" <public-webrtc@w3.org>
On Sun, Nov 13, 2011 at 9:59 AM, Stefan Håkansson <
stefan.lk.hakansson@ericsson.com> wrote:

> On 11/13/2011 03:33 PM, Justin Uberti wrote:
>
>>
>>
>> On Mon, Nov 7, 2011 at 11:51 AM, Stefan Håkansson LK
>> <stefan.lk.hakansson@ericsson.**com <stefan.lk.hakansson@ericsson.com>
>> <mailto:stefan.lk.hakansson@**ericsson.com<stefan.lk.hakansson@ericsson.com>>>
>> wrote:
>>
>>
>>     >On Mon, Nov 7, 2011 at 7:15 AM, Harald Alvestrand
>>    <harald@alvestrand.no <mailto:harald@alvestrand.no>> wrote:
>>     >> 1) We know that this stream is expected. The callback occurs as
>>    soon as we
>>     >> have the OFFER or ANSWER containing information about this
>>    stream. Move the
>>     >> last onaddstream() up to just after onconnecting().
>>     >>
>>     >> 2) We know that media is arriving on the stream. The callback
>>    occurs as soon
>>     >> as the first media packet arrives. Move the first onaddstream()
>>    down below
>>     >> the "ICE Completes" line
>>     >>
>>     >>
>>     >> My order of preference is 1) followed by 2). But I think we need
>>    to pick one
>>     >> and only one, and make sure the API spec says exactly that.
>>     >
>>     >My vote would be (1) and to add a onmediastarted() callback to
>>     >indicate the first
>>     >packet for a given media stream.
>>    I share this view - you need both. //Stefan
>>
>>
>> Agree regarding (1). Regarding (2), what do we expect the application
>> would do when it gets an onmediastarted()?
>>
> That's the indication that things worked out. (1) only indicates that
> signaling has been carried out, (2) tells the application that media is
> actually getting through. There can be problems with getting media through;
> there may FWs or NATs or other reasons for not getting it through.
>
> The application could e.g. wait with displaying the video surface until
> something is actually received. (Sure there are other ways - paint a
> canvas&analyze - but (2) is quite convenient)
>

I agree this is valuable, but typically in this case you want to wait until
the first frame is received, not just the first packet; you don't want to
start display of video until you actually have something to display.

Failure to receive media also seems like it might be a general problem for
the <video/> tag, so perhaps any notification of errors should (or perhaps
already do) happen there.

>
> As the API is currently defined, feeding back to the sender that (2) has
> happened can also be used as an indicator to the sender that the streams
> sent are received be the receiver (of course we could add error events at
> the addStream level to accomplish the same thing - but it is already there
> in some sense with (2)). So it can be part of error handling.
>
> If I had to select, (2) would be the one to keep; but both make a lot of
> sense.
>
> my $0.02
>
Received on Sunday, 13 November 2011 16:36:03 UTC

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