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

From: Robert William Fuller
Subject: [Libcdio-devel] unexpected offset in bincue.c for audio sectors
Date: Mon, 17 Mar 2008 01:27:11 -0400
User-agent: Thunderbird (X11/20071013)

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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