= SV8 specification draft =


== File header ==

|| '''Field''' || '''length (bits)''' || '''Value''' ||
|| Magic || 24 || "MP+" ||
|| Version || 8 || 0x08 ||
This file header allow old mpc readers to stop decoding at this point, without crashing.


== Block formating ==

All blocks are formated using Key / Length / Value.[[BR]]
Key is 16 bits long. It's the block ID.[[BR]]
Length is a variable size field using the same values as [http://www.matroska.org/technical/specs/index.html matroska] :[[BR]]
{{{
bits, big-endian
1xxx xxxx                                           - value 0 to  2^7-2
01xx xxxx  xxxx xxxx                                - value 0 to 2^14-2
001x xxxx  xxxx xxxx  xxxx xxxx                     - value 0 to 2^21-2
0001 xxxx  xxxx xxxx  xxxx xxxx  xxxx xxxx          - value 0 to 2^28-2
...
}}}

other way ([http://svn.mplayerhq.hu/mplayer/trunk/DOCS/tech/nut.txt?view=markup nut] way) :
{{{
bits, big-endian
0xxx xxxx                                           - value 0 to  2^7-2
1xxx xxxx  0xxx xxxx                                - value 0 to 2^14-2
1xxx xxxx  1xxx xxxx  0xxx xxxx                     - value 0 to 2^21-2
1xxx xxxx  1xxx xxxx  1xxx xxxx  0xxx xxxx          - value 0 to 2^28-2
...
}}}

what do you prefer ? I prefer the nut way

The length is the size of the block in bytes, including the key and size fields. So the minimum length of a block is 3 bytes.[[BR]]
The value is the block content. Its size can be 0.[[BR]]
All unused bits in a block MUST be 0.[[BR]]

|| '''Field''' || '''length (bits)''' || '''Value''' ||
|| Key || 16 || "EX" ||
|| Length || n*8; 0 < n < 10 || 0x1A ||
|| Value || Lentgh * 8 || "exemple" ||


== Stream information block ==

This block key is "SI".[[BR]]
This block contain the informations needed to decode the stream. This block is mandatory and must be written before the first audio block.[[BR]]

|| '''Field''' || '''length (bits)''' || '''Value''' || '''comment''' ||
|| CRC || 32 ||  || CRC 32 of the block (this field excluded). 0 = invalid ||
|| Sample count || n*8; 0 < n < 10 ||  || number of samples in the stream. 0 = unknow ||
|| Sample Frequency || 4 ||  || see table below ||
|| Channel count || 4 || 1..16 || number of channels in the stream ||
|| Audio block frames || 4 || 1..16 || number of frames in an audio block is : 2^Value^ (2..65536) ||
|| Unused || 4 ||  || must be 0 ||
|| Max used bands || 5 || 1..32 || maximum number of bands used in the file ||
|| IS used || 1 ||  || IntensityStereo. Klemm specification suggest to use the number of band always using IS ? ||
|| MS used || 1 ||  || MidSideStereo ||
|| PNS used || 1 ||  ||  ||

Frequency table
|| '''Value''' || '''Frequency (Hz)''' ||
|| 0 || 44100 ||
|| 1 || 48000 ||
|| 2 || 37800 ||
|| 3 || 32000 ||
|| 4 || 96000 ||

The CRC used in this block needs to be define.


== Replay gain block ==

This block key is "RG".[[BR]]
This block contains replay gain datas. This block is mandatory and must be written before the first audio block.[[BR]]
Values stored in dB in Q8.8 format (maybe Q7.9 or relative to the max value for the bitdepth is better ?).[[BR]]

|| '''Field''' || '''length (bits)''' || '''Value''' || '''comment''' ||
|| Version || 8 ||  || The replay gain version ||
|| Title gain || 16 ||  || The loudness calculated for the title, ''and not the gain that the player must apply'' ||
|| Title peak || 16 ||  ||  ||
|| Album gain || 16 ||  || The loudness calculated for the album ||
|| Album peak || 16 ||  ||  ||


== Encoder infomations ==

This block key is "EI".

|| '''Field''' || '''length (bits)''' || '''Value''' || '''comment''' ||
|| profile used || 4 || 0..15 ||  ||
|| unused || 4 ||  ||  ||
|| encoder version || 24 || 0-255.0-255.a-z ||  ||

== Audio block ==

This block key is "AB".[[BR]]
This block contain audio frames. The first frame is a key frame.[[BR]]
The seek elements allow to jump back or forward. The block size can be used to seek 1 block forward.[[BR]]

Seek block nb should be ( - means offset is negative) :[[BR]]
2 -2 3 -3 2 -2 4 -4 2 -2 3 -3 2 -2 5 -5 2 -2 3 -3 2 -2 4 -4 2 -2 3 -3 6 -6 2 -2 ...[[BR]]
so 2 -> 2, 3 -> 3 ... and -2 -> -2, -3 -> -3 ...[[BR]]
Allow to seek back and forward in O(ln(n)) time without a seeking table. It's something like [http://www.cipr.rpi.edu/~pearlman/papers/EI05_fastaccess_ycp.pdf this paper][[BR]]

|| '''Field''' || '''length (bits)''' || '''Value''' || '''comment''' ||
|| seek block nb || 4 || 2..17 || the number of blocks that can be skiped is 2^Value^ ||
|| seek offset || 28 || -2^27^..2^27^-1 || number of bytes to jump the blocks from the beginning of this block. 0 = invalid ||
|| audio frames || ? ||  ||  ||

== Seek Table Block ==

This block key is "ST".[[BR]]

Format have to be defined.


== Security Block ==

Checksum (MD5, SHA1) or error correcting code (LDPC).[[BR]]
Useful ?

== Tags ==

No block must be written after the last audio block to allow tagging by other applications.[[BR]]
Remarks about tagging? Incompatibilities?[[BR]]