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Re: [rtcweb] FEC for audio?

Justin Uberti <juberti@google.com> Mon, 19 May 2014 21:36 UTC

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From: Justin Uberti <juberti@google.com>
Date: Mon, 19 May 2014 14:36:04 -0700
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To: "Timothy B. Terriberry" <tterriberry@mozilla.com>
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Subject: Re: [rtcweb] FEC for audio?
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On Mon, May 19, 2014 at 12:54 PM, Timothy B. Terriberry <
tterriberry@mozilla.com> wrote:

> Peter Thatcher wrote:
>
>> Is there a good reason not to support FEC for audio, if that's what the
>> application wants?
>>
>
> I can't think of one. I think we should support FEC for audio.
>
>  On Mon, May 19, 2014 at 9:44 AM, Justin Uberti <juberti@google.com
>> <mailto:juberti@google.com>> wrote:
>>     Should we specify generic FEC for audio as well as video? Opus has
>>     built-in FEC, but it only works for the SILK portion of the payload,
>>     meaning that in high bitrate situations, it won't do much for you. I
>>     don't know if it has benefits over generic FEC.
>>
>
> The built-in FEC for the SILK layer was meant to cover the case where you
> wanted FEC with no more than one extra frame of latency, but did not want
> to double your bitrate. The reason we did not add built-in FEC for the CELT
> layer was that at the bitrates where CELT operates, we assumed traditional
> codec-agnostic FEC would be used, and thought it an adequate solution
> compared to the extra complexity a codec-specific solution would have
> required.
>
>
Thanks, that's very helpful. This means that if the app says "do FEC", and
the remote side supports opus inband FEC, and the data rate is < XX kbps,
we'll use the inband FEC instead of generic FEC.

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