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Re: PRs for either PC.createRtpSender or PC.addTrack(..., RtpSenderInit, ...)

From: Adam Bergkvist <adam.bergkvist@ericsson.com>
Date: Tue, 25 Aug 2015 07:28:27 +0000
To: Peter Thatcher <pthatcher@google.com>, "public-webrtc@w3.org" <public-webrtc@w3.org>
Message-ID: <A222C88B6882744D8D4B9681B315889024012C7A@ESESSMB307.ericsson.se>
On 2015-08-22 08:36, Peter Thatcher wrote:
> On the list we have had discussion around adding an RtpSenderInit
> parameter to PC.addTrack, and around adding PC.createRtpSender.  Today I
> realized that RtpSenderInit could also be used the same way
> PC.createRtpSender is.
>
> So, I have two PRs to choose from:
>
> PR 271 (https://github.com/w3c/webrtc-pc/pull/271):
>
> +          <dt>RTCRtpSender createRtpSender (DOMString kind)</dt>
> +
> +          <dd>
> +            <p>Equivalent to calling <code>addTrack(null)<code>, but
> +            the returned RtpSender is configured to send a track of
> +            the given <code>kind</code>.  If the returned RtpSender is
> +            later set to have a different track, that track must have
> +            the same kind.
> +          </dd>
>
> Example:
>
> var sender = pc.createRtpSender("audio");
> // ... later ...
> sender.setTrack(track);
>
> Pros:
> - Simple
>
> Cons:
> - Adds a new method (two ways to do things)
>
> PR 272 (https://github.com/w3c/webrtc-pc/pull/272):
>
> +          <dt>RTCRtpSender addTrack (
> +            MediaStreamTrack track,
> +            optional RTCRtpSenderInit senderDict,
> +            MediaStream... streams)</dt>
>
> +        <dl class="idl" title="dictionary RTCRtpSenderInit">
> +          <dt>DOMString kind</dt>
> +          <dd>
> +            <p>The kind of the track that the <code>RtpSender</code>
> +              will send.  If <code>addTrack</code> is passed a null track,
> +              this must be set to indicate the type of track that will be
> +              set later.  If <code>addTrack</code> is passed a non-null
> +              track, this kind must either be unset or agree with the kind
> +              of the given track.</p>
> +          </dd>
> +
> +          <dt>RTCRtpParameters parameters<dt>
> +            <dd>
> +              <p>The initial parameters to use for
> +                the <code>RtpSender</code>.  This is equivalent to
> +                calling <code>RTCRtpSender.setParameters</code> on the
> +                RTCRtpSender returned by <code>addTrack</code>.
> +              </p>
> +            </dd>
> +        </dl>
>
> Example:
>
> var sender = pc.addTrack(null, {kind: "audio"});
> // ... later ...
> sender.setTrack(track);
>
> Pros:
> - RtpSenderInit is useful for other things (Could be used for VAD or
> MSID replacement)
>
> Cons:
> - A little more complex
>
>
> So, which do we like?  I'd be happy with either.

Hi

I think #271 is more straight forward. It's a simple addition to the 
API. It's not possible to provide any stream here, but perhaps that's ok.

The approach in #272, with an "injected" argument, affects the most 
common usage of addTrack(), no options - just a track and a stream, and 
breaks a lot of existing code.

pc.addTrack(track, null, stream);
or
pc.addTrack(track, {}, stream);

And in the majority of cases, the "kind" member is redundant since the 
track has a kind. Also, what does it mean if its called with a 
null-track and actual streams?

I agree that the options dictionary (in #272) could be useful for other 
things, but I don't think it's a big loss since we have the RTCRtpSender 
object as an API surface.

If people don't want the extra API surface and the 
two-ways-of-doing-thinsg of createSender(), we could go with something like:

RTCRtpSender addTrack ((MediaStreamTrack or DOMString) trackOrKind,
                        MediaStream... streams);

That doesn't affect the common usage and creating an "empty" sender 
would be:

pc.addTrack("audio");

The most common case would still look the same:

pc.adDTrack(track, stream);


/Adam
Received on Tuesday, 25 August 2015 07:28:55 UTC

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