Re: [Dvdauthor-users] What is mpt when doing mpeg2desc -m ?

[Scott T. S. <sc...@ge...>]

On Fri, 2005-04-22 at 19:02 +0000, Johnny of Oz wrote:
> I have read that I can determine the audio delay in an .mpg with mpeg2desc 
> -m < [filename] . This does indeed return a value like 4770 or 6300. I know 
> you can use these as '4770mpt' to correct the audio delay.
> 
> If I determine the audio delay via another method (DVD Lab) for the same 
> files I find 53 and 70, respectively. I know these values are milliseconds. 
> By chance I found out that there is a relation with the other figures as 
> follows:
> 
> 53 * 90 = 4770
> 70 * 90 = 6300
> 
> So my question is: what is 'mpt' and how is this related to milliseconds 
> through the factor 90 (in my case anyway)???

I forget why it's called 'mpt'.  But basically the smallest atomic unit
of mpeg time is 1/90,000th of a second.  It can accurately clock both
NTSC and PAL frames (not fields), along with the corresponding audio.
Thus if you really want accurate a/v sync, you need to deal with these
units, instead of 'ms'.  This is especially important when chaining
together multiple files together and you want perfect a/v sync.

	Scott