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Re: [Libcdio-devel] unexpected offset in bincue.c for audio sectors

From: Robert William Fuller
Subject: Re: [Libcdio-devel] unexpected offset in bincue.c for audio sectors
Date: Mon, 17 Mar 2008 01:49:57 -0400
User-agent: Thunderbird (X11/20071013)

Eric Shattow wrote:
Would you suggest removing it or making it configurable at run-time?

I would remove it. The cd-paranoia included with libcdio already has a read offset correction option (-O). Similarly, my own ripper, cued, does read offset correction as well. It is easy enough for the application programmer to do read offset correction.

If we make it configurable, then we need to add it to NRG and all the other drivers as well. Adding it to the operating system drivers will be a real pain because then we have to apply an offset across sector boundaries, which means reading additional sectors. This is best done at a higher level, like the application level, which is how libcdio's cd-paranoia and cued manage it.

The most painless fix is to not change the model, but fix the bug. Even if in the long term it is decided to change the model, the bug needs to be fixed in the short term. By the way, it looks like the cdrdao driver also has a 272 byte offset, probably for the same reason the bincue driver has it.

On Mon, Mar 17, 2008 at 12:27 AM, Robert William Fuller <
address@hidden> wrote:

Does anybody know what this is about?  I'm pretty sure I know what it's
about, but I want to confirm.  I spent some time trying to figure out
why every time I re-created an image file from a rip and re-ripped from
the new image file, each new rip was progressively off by 68 more audio
samples, i.e. 272 bytes (2 channels * 2 bytes per channel * 68 samples
== 272 bytes.)  So I carefully debugged my ripper and couldn't find
anything wrong with it, so I turned to libcdio and found the source of
my troubles.  The libcdio code in question is at the end of this message.

My suspicion is that the author of the libcdio code was comparing a CD
rip with an image rip and was trying to compensate for a CD drive with a
68 audio sample read offset.  The author may not have known at the time
that almost all CD drives have some read offset, with the exception of a
few Plextors, which is why EAC, cued, and cdparanoia support read offset
correction.  If that is the case, the 272 byte offset in bincue.c for
audio sectors is emulating a CD drive with a 68 audio sample read
offset, which is probably the author's original CD drive!  I'm almost
certain we need to remove the 272 byte.  Note that this only affects
audio sectors.  Thoughts?

static driver_return_code_t
_read_audio_sectors_bincue (void *p_user_data, void *data, lsn_t lsn,
                         unsigned int nblocks)
  _img_private_t *p_env = p_user_data;
  int ret;

  /* Why the adjustment of 272, I don't know. It seems to work though */
  if (lsn != 0) {
    ret = cdio_stream_seek (p_env->gen.data_source,
                           (lsn * CDIO_CD_FRAMESIZE_RAW) - 272, SEEK_SET);

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