Re: [codec] #8: Sample rates?
stephen botzko <stephen.botzko@gmail.com> Tue, 13 April 2010 13:21 UTC
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From: stephen botzko <stephen.botzko@gmail.com>
To: "Kevin P. Fleming" <kpfleming@digium.com>
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Subject: Re: [codec] #8: Sample rates?
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Though I generally avoid MAY, this could be a case where it makes sense. Something like: CODEC MAY reduce the acoustic bandwidth at lower bit rates in order to optimize audio quality. This is free of any technology assumption about *how* the acoustic bandwidth is reduced. The MAY indicates that it is permissible. But if the CODEC algorithm doesn't need to reduce the acoustic bandwidth, then we are making no statement that it SHOULD (or SHOULD NOT). Kevin is distinguishing dynamic changes to the sample rate (for bandwidth management) from multiple fixed sample rates; and I agree that is a key distinction. I have not heard any clear application requirement for more than one fixed sampling rate. Though if there is such a requirement, IMHO we would have to negotiate the rate within SDP in the usual way, and it would affect the RTP timestamps, jitter buffers, etc. G.722.1 / G.722.1C is one precedent - it is the same core codec, but can run at two different sample rates (negotiated by SDP). Stephen Botzko On Tue, Apr 13, 2010 at 7:41 AM, Kevin P. Fleming <kpfleming@digium.com>wrote: > stephen botzko wrote: > > > Dynamically changing sample rates on the system level adds some > > complexity for RTP, since the timestamp granularity is supposed to be > > the sample rate. > > And jitter buffers, and anything else that is based on timestamps and > sample rates/counts. If the desire is for the codec to be able to change > sample rates to adjust to network conditions, then I agree with > Stephen... the 'external' sample rate (input to the encoder and output > from the decoder) should be fixed, and this is what would be negotiated > in SDP and used for RTP timestamps. The codec can downsample in the > encoder and upsample in the decoder if it has decided to transmit fewer > bits across the network. > > -- > Kevin P. Fleming > Digium, Inc. | Director of Software Technologies > 445 Jan Davis Drive NW - Huntsville, AL 35806 - USA > skype: kpfleming | jabber: kfleming@digium.com > Check us out at www.digium.com & www.asterisk.org >
- [codec] #8: Sample rates? codec issue tracker
- Re: [codec] #8: Sample rates? codec issue tracker
- Re: [codec] #8: Sample rates? Christian Hoene
- Re: [codec] #8: Sample rates? stephen botzko
- Re: [codec] #8: Sample rates? Kevin P. Fleming
- Re: [codec] #8: Sample rates? stephen botzko
- Re: [codec] #8: Sample rates? Christian Hoene
- Re: [codec] #8: Sample rates? stephen botzko
- Re: [codec] #8: Sample rates? Christian Hoene
- Re: [codec] #8: Sample rates? stephen botzko
- Re: [codec] #8: Sample rates? Roman Shpount
- Re: [codec] #8: Sample rates? Marc Petit-Huguenin
- Re: [codec] #8: Sample rates? Marc Petit-Huguenin
- Re: [codec] #8: Sample rates? stephen botzko
- Re: [codec] #8: Sample rates? Kevin P. Fleming
- Re: [codec] #8: Sample rates? Roman Shpount
- Re: [codec] #8: Sample rates? stephen botzko
- Re: [codec] #8: Sample rates? Benjamin M. Schwartz
- Re: [codec] #8: Sample rates? Raymond (Juin-Hwey) Chen
- Re: [codec] #8: Sample rates? stephen botzko
- Re: [codec] #8: Sample rates? Koen Vos
- Re: [codec] #8: Sample rates? stephen botzko
- Re: [codec] #8: Sample rates? stephen botzko
- Re: [codec] #8: Sample rates? Koen Vos
- Re: [codec] #8: Sample rates? Benjamin M. Schwartz
- Re: [codec] #8: Sample rates? Koen Vos
- Re: [codec] #8: Sample rates? Benjamin M. Schwartz
- Re: [codec] #8: Sample rates? stephen botzko
- Re: [codec] #8: Sample rates? Roman Shpount
- Re: [codec] #8: Sample rates? 44.1kHz? Michael Knappe
- Re: [codec] #8: Sample rates? Koen Vos
- Re: [codec] #8: Sample rates? Jean-Marc Valin
- Re: [codec] #8: Sample rates? Mikael Abrahamsson
- Re: [codec] #8: Sample rates? Roman Shpount
- Re: [codec] #8: Sample rates? Christian Hoene
- Re: [codec] #8: Sample rates? stephen botzko
- Re: [codec] #8: Sample rates? Roni Even
- Re: [codec] #8: Sample rates? 44.1kHz? Brian West
- Re: [codec] #8: Sample rates? Christian Hoene
- Re: [codec] #8: Sample rates? stephen botzko
- Re: [codec] #8: Sample rates? Christian Hoene
- Re: [codec] #8: Sample rates? stephen botzko
- Re: [codec] #8: Sample rates? Schwarz Albrecht
- Re: [codec] #8: Sample rates? 44.1kHz? Christian Hoene
- Re: [codec] #8: Sample rates? 44.1kHz? Koen Vos
- Re: [codec] #8: Sample rates? 44.1kHz? Christian Hoene
- Re: [codec] #8: Sample rates? 44.1kHz? stephen botzko
- Re: [codec] #8: Sample rates? 44.1kHz? stephen botzko
- Re: [codec] #8: Sample rates? codec issue tracker
- Re: [codec] requirements #8 (new): Sample rates? Koen Vos
- Re: [codec] requirements #8 (new): Sample rates? codec issue tracker
- Re: [codec] requirements #8 (new): Sample rates? Roman Shpount
- Re: [codec] requirements #8 (new): Sample rates? Jean-Marc Valin
- Re: [codec] requirements #8 (new): Sample rates? codec issue tracker
- Re: [codec] requirements #8 (new): Sample rates? Roman Shpount
- Re: [codec] requirements #8 (new): Sample rates? Raymond (Juin-Hwey) Chen
- Re: [codec] requirements #8 (new): Sample rates? Koen Vos
- Re: [codec] requirements #8 (new): Sample rates? Jean-Marc Valin
- Re: [codec] requirements #8 (new): Sample rates? Pascal Pochol
- Re: [codec] requirements #8 (new): Sample rates? Gregory Maxwell
- Re: [codec] requirements #8 (new): Sample rates? Pascal Pochol
- Re: [codec] requirements #8 (new): Sample rates? Koen Vos
- Re: [codec] requirements #8 (new): Sample rates? Jean-Marc Valin
- Re: [codec] requirements #8 (new): Sample rates? Jean-Marc Valin
- Re: [codec] requirements #8 (new): Sample rates? Koen Vos
- Re: [codec] requirements #8 (new): Sample rates? Jean-Marc Valin
- Re: [codec] requirements #8 (new): Sample rates? Pascal Pochol
- Re: [codec] requirements #8 (new): Sample rates? Butrus Damaskus
- Re: [codec] requirements #8 (new): Sample rates? Pascal Pochol
- Re: [codec] requirements #8 (new): Sample rates? Gregory Maxwell
- Re: [codec] #8: Sample rates? codec issue tracker