Re: random seeking with MAD

On Dec 1, 2003, at 12:52 AM, Jedediah Smith wrote:
> Thanks Rob, helpful stuff!
>
> But doesn't the main data pointer of the current frame come after the 
> header of the previous frame? That's how I read the ISO spec:
>
> "main_data_end - The value of main_data_end is used to determine the 
> location in the bitstream of the last bit of main_data for the frame. 
> The main_data_end value specifies the location as a negative offset in 
> bytes from the next frame's frame header location in the main_data 
> portion of the bitstream."

This seems to be from an older or preliminary version of the spec. 
There is no such field in the current ISO/IEC 11172-3. Probably the 
field was changed to main_data_begin semantics before the spec was 
standardized.

> So:
>  main_data_end for frame N-1 comes immediately after the header for 
> frame N-1
>  main_data_begin for frame N is equivelant to main_data_end for frame 
> N-1
>  thus main_data_begin for frame N comes immediately after the header 
> for frame N-1
>
> is that right?

No -- the main_data_begin for frame N comes immediately after the 
header for frame N.

Cheers,

-- 
Rob Leslie
[email protected]