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Re: Adding MIDI APIs to Audio WG Charter (was: MIDI enumeration (was: Re: getUserMedia use cases))

From: Jussi Kalliokoski <jussi.kalliokoski@gmail.com>
Date: Mon, 6 Feb 2012 21:48:19 +0200
Message-ID: <CAJhzemVQG3wWgE-KPr8ki1iEBBqassKcvbihA7j-kXOJmaSdSQ@mail.gmail.com>
To: Vilson Vieira <vilson@void.cc>
Cc: robert@ocallahan.org, Joseph Berkovitz <joe@noteflight.com>, James Ingram <j.ingram@netcologne.de>, public-audio@w3.org
Hi Vilson!

In the context of a browser, I think it's more useful to have a more
advanced API that goes well together with the existing audio and video
APIs, to allow better latency synchronization, etc.


On Mon, Feb 6, 2012 at 9:43 PM, Vilson Vieira <vilson@void.cc> wrote:

> Hi all,
> when I think in MIDI devices as input in the browser I just think in a
> wrapper API to a MIDI lib like PortMidi. Am I wrong?
> Cheers.
> 2012/2/6 Robert O'Callahan <robert@ocallahan.org>
>> On Tue, Feb 7, 2012 at 5:28 AM, Jussi Kalliokoski <
>> jussi.kalliokoski@gmail.com> wrote:
>>> I put together a gist in the form of IDL of what MIDI in the browser
>>> could look like, respective of MediaStreams Processing API and getUserMedia
>>> API. Excuse my weak skills in IDL, I hope it suffices to introduce my idea.
>>> It's also a bit incomplete, for example, it doesn't describe how to
>>> actually push the midi stream to the MediaStreamProcessor, because I
>>> haven't thought of a good way to do it yet. I also included an example
>>> usage.
>>> https://gist.github.com/1752949
>>> Feedback appreciated.
>> To make sure you can get MIDI data for all input streams to a
>> ProcessedMediaStream, I'd give each MediaInputBuffer an array of MIDIEvent
>> objects comprising the MIDI data for the first MIDI track, and give
>> ProcessMediaEvent a writeMIDI() method that lets you write an array of
>> MIDIEvents to the stream output. Maybe it's necessary to support multiple
>> output MIDI tracks for a single stream?
>> Also, ProcessMediaEvent already has an 'inputTime', which probably means
>> the same thing as "sampleTime".
>> We also need to discuss whether main-thread access to MIDI data streams
>> is worth having. Most of the time you want the latency and performance
>> benefits of handling the data in a Worker, and it's trivial to have a
>> worker send and receive data to the main thread if needed, so a dedicated
>> main-thread API may not be needed.
>> There's a whole separate conversation to be had about how devices should
>> be accessed and enumerated and how the UI could work. This is mostly an
>> API-independent issue. In general it's probably best if the app can specify
>> its requirements declaratively up front --- e.g., the sort of devices it
>> wants to talk to --- and let the browser, interacting with the user, decide
>> which devices to connect to (and remember that decision between runs). That
>> reduces the amount of trust the user has to give the app.
>> Rob
>> --
>> "If we claim to be without sin, we deceive ourselves and the truth is not
>> in us. If we confess our sins, he is faithful and just and will forgive us
>> our sins and purify us from all unrighteousness. If we claim we have not
>> sinned, we make him out to be a liar and his word is not in us." [1 John
>> 1:8-10]
> --
> Vilson Vieira
> vilson@void.cc
> ((( http://automata.cc )))
> ((( http://musa.cc )))
Received on Monday, 6 February 2012 19:48:46 UTC

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