[Mjpeg-users] Re: mpeg2enc options for SVCD

[Matti H. <mat...@ni...>]

Bernhard Praschinger:

>>ppmtoy4m: -v 0 -S 420_mpeg2 -L -I b -F 600:24 -A 8:5
>>mpeg2enc: -v 0 -f 4 -F 3 -n p -a 2 -b 2500 -I 1 -r 16 -q 7 -Q 2 -V 256
>
>You do not need to specify -a 2 because 2 is the default, the same with
>-I 1.

Yes, I know some options are redundant but I have included them just 
to learn them and those default strings also act as templates so I 
can change their values easier.

I vaguely remember reading somewhere that mpeg2enc defaults to 
interlaced output if the input resolution goes over a certain limit?

>Why do you use that strange defaults for ppmtoy4m (I hope the third p is
>an accident) for -F an -A ? Because I think mpeg2enc has no option for
>encoding a that unusual pixel aspect ratio (-A).

-A 8:5 in ppmtoy4m is filled by MediaPipe GUI.

Also I wondered where that 8:5 came from until I discovered that, for 
example, if the output is PAL 480 x 576, then 480x(8:5) x 576 = 768 x 
576 which is "True" computer square-pixel resolution. The same 
MediaPipe default calculation seems to apply to other resolutions as 
well. But based on my tests, omitting -A 8:5 didn't seem to make any 
difference in the final output dimensions via TV so I guess I can 
just take it off.

BTW, there is a nice page describing these obscure Digital Video 
Resolution and Aspect Ratio Conversions at:

<http://www.iki.fi/znark/video/conversion/>

>Also which frame rate do you relly have, I do not know a norm that has
>600:24. I gues you want NTSC so your ratio will be 30000:1001 or
>60000:1001.

600:24 = 25, i.e. PAL frame rate. The interlaced output is OK with 
this setting although now I wonder whether I should use 1200:24 = 50 
which is PAL field rate? Oh, so many options...

>When you rest the frame rate to a correct size you do not hat to use the
>mpeg2enc -n p option.

-n p (PAL) seems to be the default so there is another redundant 
option at least for PAL users.

>The -q option controls the minimum quantization of the output stream.
>Quantization controls the precision with which image information is
>encoded. The lower the value the better the image quality.

Thanks for the clarification.

>  BTW, I have a SVCD on a Macintosh memo and cookbook at:
>  <http://www.sjoki.uta.fi/~shmhav/SVCD_on_a_Macintosh.txt>
>
>If you want I cann ad it as a reference to the howto.

Please do but remember also the great RNC's Guide to SVCD on Mac 
which has taught me a lot:

<http://homepage.mac.com/rnc/>

Many thanks for your comments. I really appreciate your help,


-- 
Matti Haveri <mat...@sj...> <http://www.sjoki.uta.fi/~shmhav/>