Howdy,
> -----Original Message-----
> From: Leonid A. Kulakov [mailto:[EMAIL PROTECTED]]
> Sent: Friday, April 28, 2000 3:33 AM
> To: [EMAIL PROTECTED]
> Subject: Re: [MP3 ENCODER] MP3Enc upsampling /buffer
>
> I've got some points on this issue.
>
> 1. ISO docs has a number of errors and typos, this can be one of them.
> May be authors wanted to set buffer restriction to maximum, but
> forgot that maximum frame size corresponds to maximal bitrate
> and MINIMAL samplerate and took both maxima for computation?
> p. 2.4.3.4.4 in ISO 11172-3 is not apparent enough to be the truth.
It is pretty clearly wrong to use max bitrate and max samplerate when min
samplerate produces a larger value.
I'm not sure what ISO mean by the final sentence of the section under
consideration, "At sampling frequencies lower than 48 kHz the buffer should
be constrained such that the same physical buffer size is sufficient as the
one calculated for the for the 48 kHz case above." The sentence seems to
contradict itself (and is not grammatically correct in any case - does
anyone have a non-English version of the spec which makes more sense?) - how
can the buffer be constrained in a variable way to the same size? Is it
possible to interpret this clause to mean that the buffer size should be
adjusted up for lower samplerates?
> 2. I use 1440+512 bytes (11520 + 4096 bits) buffer in decoder.
> If any bitstream uses frame buffer > 7680 bits - not a problem.
I do a similar, but less smart, thing in my decoder. I use 7680 + 4096 bits
for the buffer, where 7680 is the 'maximum' frame size (though I only ever
buffer main/ancillary data) and 4096 is the max main_data_begin. I think I
may switch it to yours above. In any case, in software it's just a #define,
and most machines have RAM to burn these days...
> I'm sure every decoder should decode (and play music)
> rather then locate incompliances in bitstream. 1 KB is not a cost.
Amen.
...
> > Maybe Alex Broadhead could comment on if the decoder he just
> > wrote could handle this?
Sorry, I was off for a few days there.
My decoder has the buffer limitations above. Since we basically always run
at 64 kbit stereo, I could probably make my buffer much smaller, but I'm
trying to be a compatible as I can for now. If I ran into a bitstream that
crashed my decoder for buffer reasons, I'd definitely just up the size.
I should note, BTW, that the ISO 'dist10' package uses a BUFFER_SIZE of 4096
bytes... Doh.
Alex
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