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Re: [AVT] Working group last call: JPEG-2000 payload format



On 9 Jun 2007, at 00:30, Dave Singer wrote:
At 9:15 -0700 6/06/07, Chuck Harrison wrote:
Suppose

1. A compliant J2K receiver MUST accept 90kHz timestamps
2. A compliant J2K receiver MAY accept other timestamp rates
3. A compliant J2K sender SHOULD transmit 90kHz timestamps
4. The RFC warns that senders violating the SHOULD of item 3
    risk interoperability problems.

I think timestamp conversion tends to be a common function in an RTP stack, doesn't it? Be that as it may, it's no good allowing me to send non-90KHz if I can't know it'll work -- standards are about interoperability.

Right - this is the problem with allowing multiple rates.

So I think that it should say

* a 90 KHz clockrate is recommended (you could even use SHOULD be used) for JPEG 2000 streams

SHOULD, I think.

* receivers MUST be able to handle other clock rates

The RFC warns that if you choose an unsuitable rate, or a rate whose conversion is difficult, error-prone (e.g. to round-off errors), or even unusual, you risk playability problems.

...and the offer/answer considerations section in the draft explains how to negotiate the desired rate, and how to interact with receivers that only support 90 kHz.


--
Colin Perkins
http://csperkins.org/



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