commit 8baabbe3924d189a5f06f6ced33512b8e8f35a4c
Author: Matteo Cypriani <mcy@lm7.fr>
Date:   Wed Dec 7 05:07:13 2016 +0100

    Update page 'Home'

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+# About the NRG image format
+
+A good reference about the metadata format is the corresponding Wikipedia
+article: <https://en.wikipedia.org/wiki/NRG_(file_format)>.
+
+The source code and comments of NRGrip also provide some information, of
+course.
+
+
+# Manual audio data extraction howto
+
+Just for fun, it is possible to extract manually the audio data from an NRG
+image, after displaying its metadata with NRGrip. You will need to know:
+
+- The first audio byte (`dd skip`):
+  `daox.first_track.index1` (or `index0` if you wish to include the pre-gap)
+
+- The last audio byte:
+  `daox.last_track.end_of_track`
+
+- The number of audio bytes (`dd count`):
+  `Last audio byte - First audio byte`
+
+To extract the raw audio data (substitute `${FIRST_AUDIO_BYTE}` and
+`${NB_AUDIO_BYTES}` with the numbers found above:
+
+    dd iflag=count_bytes,skip_bytes if=image.nrg of=image.raw \
+      bs=4M skip=${FIRST_AUDIO_BYTE} count=${NB_AUDIO_BYTES}
+
+
+# Notes on cue sheet extraction
+
+From Wikipedia:
+
+- A CD can contain up to 99 tracks.
+- Each track can in turn have up to 100 indexes.
+- The vast majority of songs are recorded under index 1, with the pre-gap being
+  index 0.
+- Sometimes hidden tracks are placed at the end of the last track of the disc,
+  often using index 2 or 3.
+- In an NRG cue sheet, the _index0_ points are present even when they are
+  identical to the _index1_ ones.
+- The _index0_ points in audio tracks are incorrect if Nero has been asked to
+  record all the sub-channel data (in that case the sector size is 2448 bytes).
+- No index other than 0 or 1 has been encountered, although the chunk format
+  allows for such cue points to be recorded; thus the number of cue blocks seems
+  to always be `2 * (number of tracks + 1)`: two indices for each track, an
+  _index0_ for the lead-in and an _index1_ for the lead-out.
+
+From this information and other observations:
+
+- The cue sheet should include all the indices for each track, but _index0_
+  should be ignored if:
+  - _index0_ = _index1_, or
+  - _index0_'s position is negative.
+- It is possible to have incoherent track numbering (observed: track 10 is
+  numbered 16 in CUEX).
+- The lead-in area (track 0) and the lead-out area (track 0xAA) should not
+  appear in the cue sheet.
+
+How will multi-session CDs be handled? Is it worth implementing, since
+multi-session audio CDs must be very rare?
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