Author: ods15 Date: Sat Oct 28 20:29:06 2006 New Revision: 165 Modified: trunk/docs/nut-english.txt Log: Explain VLC's... Modified: trunk/docs/nut-english.txt ============================================================================== --- trunk/docs/nut-english.txt (original) +++ trunk/docs/nut-english.txt Sat Oct 28 20:29:06 2006 @@ -43,6 +43,20 @@ reserved fields which can be skipped by old demuxers, and a CRC covering the packet from after the packet_header until the CRC itself. +Variable Length Coding + +Almost all fields in NUT are coded using VLCs. VLCs allow for compact +storage of small integers, which still being extendible to infinitely +large integers. The syntax is of a VLC is, per byte, a 1 bit flag stating +if there are more bits to the integer, and 7 bits to be prepended to the +lsb of the integer, shifting the previous value to the left. +Stuffing is allowed in VLCs by adding 0x80 bytes before the actual value, +but a maximum of 8 bytes of stuffing is allowed in any VLC outside of a +NUT packet. The only such fields are forward_ptr and fields in frame +headers. This is to prevent demuxers from looping on a large of amount of +damaged bytes of 0x80. Fields inside a NUT packet are protected by a CRC +whcih can be checked before decoding. + Header Structure A NUT file must begin with a magic identification string, followed by