Re: Constraints and MediaRecorder

On Sun, Feb 9, 2014 at 9:28 AM, Eric Rescorla <ekr@rtfm.com> wrote:

> On Mon, Feb 3, 2014 at 4:04 PM, Robert O'Callahan <robert@ocallahan.org>wrote:
>
>> On Tue, Feb 4, 2014 at 12:25 PM, Eric Rescorla <ekr@rtfm.com> wrote:
>>
>>> I agree that this is true to some extent, but TBH I found it more
>>> convincing before your post above suggesting that capability testing
>>> might consist of empirically verifying that the browser did what it
>>> promised it did. From the perspective of the consumer of the API,
>>> what I want is deterministic behavior and that includes errors when
>>> I ask for something the UA won't.
>>>
>>
>> OK, but the Web likes graceful degradation when feasible. That's why we
>> don't throw errors when you use an unsupported CSS property in a
>> stylesheet, and why 2D canvas silently skips rendering operations when
>> given NaN parameters. This is partly because the Web has a cohort of
>> mediocre developers and poorly maintained apps, partly because the Web has
>> heterogenous implementations with different levels of API support, and
>> partly because Web implementations compete on how many apps they can run so
>> economics favour permissiveness. (There are yet other reasons applying to
>> specific examples.) Having said that, I appreciate that degree of
>> permissiveness involves tradeoffs that have to be analyzed on a case by
>> case basis.
>>
>> In this case we have some consumers who want to provide optional
>> constraints, and others who want to provide mandatory constraints, and
>> providing a single API that provides both without confusing anyone over its
>> semantics is a bit hard. If we go with only optional constraints, and let
>> people implement mandatory checking via inspection APIs that we'll probably
>> have to provide anyway, it feels like a win to me.
>>
>
> I'm still finding myself confused about what you mean by "inspection APIs"
>
> Say, for instance, that I want the MediaRecorder to record at 192 kHz.
>
So we have some mechanism for me to ask for that and then the browser
> gives me back a MediaRecorder with some properties it thinks are
> appropriate. Are you arguing that there should be some API that will
> allow me to interrogate the object and see what I got (which would
> have to exist for every constraint, presumably) or that I have to
> directly test the object for its properties, e.g., by passing in audio
> and then seeing if it retains the high frequencies?
>

The former --- assuming there's a use-case where you really need to know,
at the time of recording, whether those frequencies are being recorded.

Rob
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