LPCM headers

[SMurf]

Hi,

I'm looking into developing a multiplexer that supports LPCM and after searching on the net for a while I found the header for it:-

number of frames: 8 bits
first access unit pointer: 16 bits
audio emphasis on-off: 1 bits
audio mute on-off: 1 bits
reserved: 1 bits
audio frame number: 5 bits
quantization word length: 2 bits
audio sampling frequency (48khz = 0, 96khz = 1): 2 bits
reserved: 1 bits
number of audio channels - 1 (e.g. stereo = 1): 3 bits
dynamic range control (0x80 if off): 8 bits
(total 6 bytes)

I understand nearly all of it, except the first access unit pointer, audio frame number and quantization word length. If the number of frames is stored in eight bits, how could the audio frame number only be in five? Is the quantization word length actually used for something (Not from the DVD I've got)? :confused:

[mpucoder]

The first three bytes are the same for all formats, so don't let the field sizes throw you.
The first access unit is a concept that applies to compressed audio that packages into frames, these are not related in any way to the video frames. An example: AC3 uses 32ms frames. The value is a relative offset into the stream. This also points to the sample which represents the PTM value.

Quantization word length values are the same as an audio header in an .ifo 0=16, 1=20, 2=24, 3=DRC. DRC doesn't apply to LPCM, either.