Re: [cdg123-devs] Extracting CD+G CDs on Linux

[Miguel R. <yo...@mi...>]

Hi,

El Lunes, 6 de Septiembre de 2004 14:58, Steve Fosdick escribi=F3:
> Hi,
>
> I was looking for a CD+G player for Linux and found this project.  I have
> downloaded and built libcdg123 and libxmms_cdg123 so the next step was to
> see if I could get input data in the right format while reading the CD+G
> disc on Linux.
>

I hope you have the version 0.0.2 of the plugin, as it fixes an audio/graph=
ics=20
sync problem.

> I have found the cdrdao command claims to be able to extract sub-channel
> information from a CD provided the CD-ROM drive supports this.  In my case
> the drive did though I was only able to get this to work in raw mode
> (option --read-subchan rw_raw).  In this mode cdrdao appears to write a
> single file consisting of a series of 2448 sectors each being the 2352
> bytes of audio data followed by the 96 bytes of sub-channel data.
>

I extracted some CD+G info with cdrdao a few months ago. It is possible to =
do=20
but requires a lot of options tunning.

> I was able to use the TOC file generated by cdrdao to split the tracks
> appart and then splitting the audio and sub-channel data by reading chunks
> of 2448 bytes at a time and writing the first 2352 to the audio file and
> the next 96 to the sub-channel file.
>
> Playing the resulting files with the XMMS plugin doesn't work though - the
> SDL output window cycles between black and blue backgrounds with occasion=
al
> junk appearing on the screen.  This makes me think that the format of the
> .cdg file may not be the same as the sub-channel data from the disk or th=
at
> the sub-channel data may still need rearranging in some way before
> libcdg123 can process it.
>

The format of the .cdg in actually the same as the subchannel data. Each CD=
=2DDA=20
frame (96 bytes) can contain up to 4 cdg frames (24 bytes each). The fact=20
that the SDL window changes color means that there is something on the file=
,=20
as libcdg123 first checks if the frame is really a cdg frame before drawing=
=20
it.

I am working on a new package called cdgutils that basically will contain s=
ome=20
utils to extract, rip and so cdg information. But ripping subchannels in=20
Linux is almost impossible, at least in a generic way valid for most drives.

> Is there a specification for the .cdg file format available publicly and =
is
> an extract of the .cdg test file available from anywhere?

I attach the document cdgrevealed, which I used to write libcdg123. Also it=
=20
might be a good idea to look at the source code of libcdg123, specially for=
=20
the part of XOR tiles, as it's difficult to figure how it works from the=20
document.

 Miguel