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

Re: MediaStream Recording options

From: Greg Billock <gbillock@google.com>
Date: Sun, 21 Jul 2013 23:31:16 -0700
Message-ID: <CAAxVY9fetiQ0V15i4cEiDNZz70Mbxg646bvwcrz8_d8SHLUstw@mail.gmail.com>
To: Jim Barnett <Jim.Barnett@genesyslab.com>, Harald Alvestrand <hta@google.com>
Cc: "public-media-capture@w3.org" <public-media-capture@w3.org>
Thanks, Jim and Harald. Encoding options are a big black hole, obviously.
:-(

I think if we use MediaTrackConstraints for this, we should mimic the
MediaStreamTrack API ("constraints()/applyConstraints()") -- or perhaps
have that mimic the recorder API if getConstraints/setConstraints is
preferable -- so it's hinted they're the same type. Is that what you had in
mind when you mentioned hoping to just be able to grab the type and
semantics from a parallel instance? Or is there another potential spot to
get it from?





On Fri, Jul 19, 2013 at 12:00 PM, Jim Barnett <Jim.Barnett@genesyslab.com>wrote:

>  Greg,****
>
>   In general, get/setOptions is the least mature part of the spec.  Iíve
> been hoping that I would be able to inherit the options/settings interface
> from another spec, but so far that hasnít worked out.   Further comments
> in-line.****
>
> ** **
>
> *From:* Greg Billock [mailto:gbillock@google.com]
> *Sent:* Friday, July 19, 2013 2:44 PM
> *To:* public-media-capture@w3.org
> *Subject:* MediaStream Recording options****
>
> ** **
>
> A couple more questions about the getOptions/setOptions methods.****
>
> ** **
>
> First, these APIs look dual, but in fact getOptions returns the set of
> available options, not the options that have been set with setOptions.
> Should this be renamed getAvailableOptions instead? That the
> RecordingSettings and AvailableSettings are different types is a bit
> confusing as well. Would renaming the methods be ergonomic enough to go
> with a single RecordingSettings type?****
>
> >> Something like this would make sense, but again Iím hoping to inherit
> the API from another spec, so that all the Recording spec would have to do
> is to define the specific options that it uses.****
>
> ** **
>
> Having getOptions return the set of current options might still be a good
> idea.****
>
> ** **
>
> Second. Are the options meant to be user-consumed? That is, is the idea
> that retrieved options can be presented to the user? Or is this meant to
> just be manipulated directly by app code?****
>
> >> Theyíre mostly intended for app use.  We havenít really thought about
> presentation to the user.  I wonder if weíd want an additional pretty-print
> name or something like that.  ****
>
> ** **
>
> Third. Have you considered options relating to audio sampling? For example
> a "audioBitDepth" and "audioSampleRate" might be really nice. I'm guessing
> this set of options is intended as the spot where further encoding options
> can be added in. How many of these are intended to go here directly as
> settings keys as opposed to, say, params on the mime type?****
>
> ** **
>
> >> We really havenít thought about this part.  ****
>
> ** **
>
> Fourth. "imageWidth" and "imageHeight" sound like photo capture sizes. The
> comments on AvailableSettings makes it sound like this is capture size for
> video as well, though. Is that right? Will this crop, downsample, or what?
> I think this could use some additional documentation. Should these
> parameters, for video, echo the names in MediaTrackConstraints? "width",
> "height", "frameRate", etc.****
>
> >>  They may have started off as photo settings, and then not been
> properly renamed when photo was moved to a different spec.   Might it
> confuse people if they echo the names for the MediaTrackConstraints?  Iím
> not sure.   Thereís been a fair amount of discussion about how the UA
> may/should/must implement MediaStream constraints.  The rough conclusion
> has been that it can either use the settings on the underlying device, or
> do postprocessing, but itís not allowed to fake data (in other words, it
> can downsample, but not upsample.)  I imagine that similar considerations
> apply here, but we havenít written it  up yet.  This, again, is something I
> would like to inherit from another spec (i.e. the general syntax and
> semantics of settings.)****
>
> ** **
>
> Fifth. Is "takePhoto" and associated image parameters redundant to
> MediaStream Image Capture? Any reason to have them in both spots?
> Presumably the pre-encoding image capture will be lower latency and higher
> fidelity.****
>
> >> No, theyíre redundant and I have removed them from the editorís
> draft.  They were originally in the recording spec, then moved to a
> separate spec.  ****
>
> ** **
>
> Thanks!****
>
> ** **
>
> -Greg Billock****
>
> ** **
>
> ** **
>
Received on Monday, 22 July 2013 06:31:43 UTC

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