W3C home > Mailing lists > Public > public-media-capture@w3.org > April 2013

Re: new draft of recording

From: Robert O'Callahan <robert@ocallahan.org>
Date: Tue, 2 Apr 2013 15:12:59 +1300
Message-ID: <CAOp6jLZJRdM6Jzmqr-333X3ccgEq-LrEEaO_k_gHkYdVf3+65Q@mail.gmail.com>
To: Travis Leithead <travis.leithead@microsoft.com>
Cc: Jim Barnett <Jim.Barnett@genesyslab.com>, "public-media-capture@w3.org" <public-media-capture@w3.org>
On Tue, Apr 2, 2013 at 10:35 AM, Travis Leithead <
travis.leithead@microsoft.com> wrote:

>  OK. What does 'imageHeight' mean? I thought it was the image height the
> UA had selected after capturing has begun. Are you saying it's the height
> the author requested via setOptions? How is it supposed to be used by apps?
> Maybe we should just remove it?
> >Ditto for the MIME type. An app can get that from the first Blob
> delivered, can't it?****
> These properties report what the recorder is currently configured to—which
> might be different than the options you provided—especially since the
> constraints you provide might only specify a particular range of
> values—you’ll eventually want to know exactly what the proportions are. For
> mimetype, it seems common enough to want to know in advance of starting
> recording, whether the format you want is supported.

It seems to me quite constraining for the implementation to have to figure
out the imageWidth/height and MIME type synchronously, if there are
external frameworks involved or the automatically-selected MIME type
depends on track contents. If we had canRecordType as I suggested then it
would be easy for the app to query whether a format is supported. So I
suggest removing those attributes.

> ** **
>   The utility of stop/start/pause/resume events seems questionable. These
> happen in response to method calls on the MediaRecorder, so authors already
> know when these things are happening. Are there use-cases where these
> events are useful?****
> >> The idea is that these are asynchronous commands, and the app needs to
> know when they actually go into effect.  This is particularly the case for
> start(), which can be called before any media is available.  I’m less sure
> of the case for pause/resume, but the events were added for consistency.
> In general , stop/pause/resume should take effect quite quickly, but there
> can be a long delay before a call to start() produces any actual recording.
> ****
>  >It's not clear to me why an app would care when recording started
> (especially since the event fires async and can therefore be delayed a
> while after the actual start). Can you give an example where these events
> are needed?****
> Imagine a UI that wants to provide feedback based on when a stream
> actually starts recording, vs. when the users presses the record button.
> I’ve seen at least a few UIs that use an “armed” state to represent this
> interim period.

OK I guess. What about stop, pause and resume?

> At one of our prior F2F meetings, one of the use cases for warnings was to
> alert the user if the inbound stream configuration changes in such a way
> that could still be supported by the recorder, but might be something the
> code would want to respond to. For example, new tracks being added/removed
> while recording.

That's covered by track add/remove events already specced on MediaStreams.

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Received on Tuesday, 2 April 2013 02:13:26 UTC

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