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Re: What would you like to see in WebRTC next? A low-level API?

From: Harald Alvestrand <harald@alvestrand.no>
Date: Fri, 2 Feb 2018 09:01:05 +0100
To: Toshiya Nakakura <t.nakakura@kmd.keio.ac.jp>, Sergio Garcia Murillo <sergio.garcia.murillo@gmail.com>, Lennart Grahl <lennart.grahl@gmail.com>, public-webrtc@w3.org
Cc: Martin Thomson <martin.thomson@gmail.com>
Message-ID: <5134f8c4-b91c-a957-8158-2d6440e0fa05@alvestrand.no>
Every time I talk to real video people about the need for
synchronization, they say "SMTPE timecodes".
We've largely ignored those in WebRTC, but do they have a place?

On 02/02/2018 02:00 AM, Toshiya Nakakura wrote:
> Thank you for this fruitful discussion.
> Yes, JavaScript programs cannot handle RTP-binary currently.
> In the case which user handle data generated in JavaScript on Browser,
> the metadata plan would works perfectly.
> In my case, we need to consider getUserMedia API or another API which
> offer tactile data to JavaScript programs.
> I am sure you already know about this but video follows this flow.
> (A-1)get raw data -> (A-2)encode -> (A-3)generate RTP packets ->
> (A-4)transmit(on MediaStream) -> (A-5)extract payload -> (A-6)decode
> -> (A-7)buffering -> (A-8)play
> Also, tactile data follows this flow.
> (B-1)get raw data -> (B-2)encode -> (B-3)packetize -> (B-4)transmit(on
> DataChannel) -> (B-5)de-packetize -> (B-6)decode -> (B-7)buffering ->
> (B-8)play
> In the metadata plan, (B-1)processes in JavaScript programs need to
> set metadata to (A-1)process in Browser, and (B-7)processes also need
> to get metadata from (A-7)process.
> Then browsers also need to offer methods and event triggers for
> (B-1)and(B-7).
> Ideally, it is the best if Browsers have tactile encoders and decoders
> like video in the future.
> Currently, my program gets tactile data through serial device API for
> Chrome App.
> As for the getUserMedia, I have one more problem.
> In my understanding, one getUserMedia API call grabs only one camera.
> To make a 3D vision, videos from two eyes must be synchronized perfectly.
> But the synchronization between medias from another getUserMedia API
> calls isn't supported.
> Best Regards,
> Toshiya Nakakura
> On 2018年02月01日 20:41, Sergio Garcia Murillo wrote:
>> AFIK the problem is that the rtp timestamp is not know until after
>> the video frame is encoded very deep on the video processing
>> pipeline, so it is not possible to retrieve it on js at sending time.
>> Best regards
>> Sergio
>> On 01/02/2018 11:50, Lennart Grahl wrote:
>>> I really am not an expert when it comes to A/V but there's a timestamp
>>> field in the RTP... if the API would allow to retrieve that value
>>> (.currentTimestamp) when sending and wait for it when receiving
>>> (.waitForTimestamp(timestamp))... shouldn't that work?
>>> Cheers
>>> Lennart
>>> On 01.02.2018 08:22, Sergio Garcia Murillo wrote:
>>>> If you can send a metadata payload within rtp, you can sync with
>>>> external sources. Jus' sayin' ;)
>>>> For example, if you create a json object with an uuid and send it via
>>>> datachannel, you could send that uuid in the rtp metadata.
>>>> Then on the receiving side you could get an  onmetadata event on the
>>>> media stream track, retrieve the uuid sent by rtp and sync it with the
>>>> data sent via datachannel.
>>>> If the json is small, you could even send the full json on the rtp
>>>> metadata and not even send it via datachannels.
>>>> Best regards
>>>> Sergio

Surveillance is pervasive. Go Dark.
Received on Friday, 2 February 2018 08:01:47 UTC

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