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Re: [Libcdio-devel] Re: isrc API?

From: Peter Creath
Subject: Re: [Libcdio-devel] Re: isrc API?
Date: Thu, 20 Mar 2008 12:02:32 -0400

On Wed, Mar 19, 2008 at 11:33 PM, Robert William Fuller
<address@hidden> wrote:
>  Basically, READ SUB-CHANNEL is a great interface for displaying track
>  time when you're playing a disc.  It otherwise sucks.  That is why in
>  cued I use MMC READ CD to get the Q sub-channel data.  It works at high
>  speed and it doesn't play music.  It's great for ripping.
>  Unfortunately, not all drives support reading the Q sub-channel with MMC
>  READ CD because that part of MMC READ CD is optional, and there's no
>  feature test to answer the question "does MMC READ CD support reading
>  the Q sub-channel?"

You're definitely right to avoid the READ SUB-CHANNEL command.  I
remember looking into it some time ago and thinking it was a mess too.

But what about using READ CD to read RAW P-W subchannel data?  I
thought RAW P-W was more widely supported, as it required the drive to
do less.  (It's still optional, but it's a lot easier to implement
than Q extraction.)

I also thought that reading RAW P-W allowed you get a better sync with
the audio, whereas Q was not guaranteed to be sector-matched with the
audio you're playing.

Among other things, it looks like RAW P-W format (2448 = 2352+96) can
also be used to get the subchannel data for the disc lead-in.  I
doesn't appear that you can do that with just Q queries.  And P-W
seems to be required to support CD+G, if we ever get there.

So what do you think about issuing a RAW P-W read and then extracting
whatever subchannels you want in software?

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