Subject: Re: [linux-audio-dev] MTC, SMPTE, etc.
From: Maarten de Boer (maarten.deboer_AT_iua.upf.es)
Date: Fri Jul 21 2000 - 12:50:40 EEST
> I know that my applications could/would not use it via the
> sequencer. I don't like the sequencer much at all, not because of the
> implementation but because of the concept.
>
> I would much rather have a C++ (or C) function that accepted
> audio data in, and returned SMPTE time, and another than accepted
> SMPTE time and returned a buffer of audio data.
Yes, I understand that. Right now my code is not reentrant. I will
move some statics to structs, so it will be possible to use it as
a library.
> >About jitter: of course the audio input buffer size adds jitter to the
> >SMPTE. I am not sure if this is a problem. The SMPTE time could be
> >adjusted accordingly...
>
> I don't think you necessarily mean jitter, do you ? More like latency?
> Unless you're referring to times when the SMPTE signal crosses the
> fragment (interrupt) boundaries ?
Yes, that is exactly what I am refering to. Theoratically, when the SMPTE
would have a constant speed, the fragment size could be set to always
contain exactly one SMPTE frame. But SMPTE speed is not fixed, and also
not all sound cards allow sample-accurate setting of the fragment size.
Imagine we use a fragment size of 256, at 22050 Hz (which I found sufficient
to recognize the SMPTE), we can be 0.012 sec off. At 30 SMPTE frame/sec, this
is more than a third of the SMPTE frame duration.
Maarten
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