Re: [Mjpeg-users] mpeg2enc options for SVCD

[Bernhard P. <sha...@ut...>]

Hallo

> pppmtoy4m: -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
> 
> BTW, I noticed that currently the QuickTime input file's High Quality
> flag must be set and saved with QuickTime Pro 6 before encoding,
> otherwise the output is progressive if using mpeg2enc via MediaPipe.
> For progressive output it seems to be best to leave the QuickTime
> input file's High Quality flag unchecked.

> - Have I understood correctly that in mpeg2enc -f 4 (SVCD) ignores -b
> -r -g -G and sets them to -b 2500 -r 16 -g 6 -G 18 no matter what?
mpeg2enc sets som things by default. If you want to override the
options, you should use -f 5, than you can override the mpeg2enc
defaults. 

You do not need to specify -a 2 because 2 is the default, the same with
-I 1.
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). 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.

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

> - Does it matter whether I use -f 5 (user SVCD) or -f 3 (Generic
> MPEG2) to override -b -r -g -G while encoding a lower bitrate SVCD or
> a higher bitrate and/or an odd resolution (PAL 352x288 or 720x576)
> XSVCD?
If you want to create a SVCD you have to use -f 4/5. I think I answered
your question aboth. 

> - ./mpeg2enc -help says about -q that "Image data quantisation factor
> [1..31] (_1_ is _best_ quality, no default)" but the mjpeg tools
> howto 1.6.0 says "The -q option controls the minimum quantization of
> the output stream. Quantization controls the precision with which
> image information is encoded. The _higher_ the value the _better_ the
> image quality". This leaves me puzzled:
This it a typing mistake in the howto. The new version (CVS) or HTML on
SF hast this problem corrected. 

The correct version in the howto is:
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.

> So is -q 7 better or worse than -q 3 at -b 2500? Should I lower or
> increase -q with lower than 2500 bitrates??
There you take a second look on the howtos subsection: Which values
should be used for VBR Encoding

> - What does mpeg2enc -Q actually do (Quantisation-reduction, Max.
> quantisation reduction for highly active blocks [0.0 .. 5] (default:
> 0.0))? Is -Q 2 OK?
I never use it. 

> - Is there an upper limit for the -V (Target decoders video buffer
> size in KB) for DVD players? mpeg2enc fails with the default -V 46
> with -f 5 so I have used -V 256 which succeeds with up to 10036 kb/s
> or 9.8 Mb/s DVD-like bitrates.
If you have a DVD Player, in VCD/SVCD mode, You have to try which buffer
it accepts. VCD allowes only 46k (which is also default). For SVCD (-f
4/5) you can set your own) but mpeg2enc has a default here. (I use 300k)

I have never heard of a buffer size a DVD player must have. If you want
to creat DVDs (-f 8) the default value for the buffer size works well. 

> - When is it recommended to use -d (Don't generate of dummy SVCD
> scan-data for the ISO CD image generator "vcdimager" to fill in) or
If you do not use vcdiamger afterwards, or if you encounter problems
playing the streams with the dummy svcd SOF back. 

> -C (Force SVCD horizontal_display_size to be 480 - standards say 540
> or 720 But many DVD/SVCD players screw up with these values)?
I think the mpeg2enc manpage explains everything. Just try encoding with
that Option. If your player does not play the stream at the correct
width you have tho use that option.

> 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. Or any other
suitable document. 

auf hoffentlich bald,

Berni the Chaos of Woodquarter

Email: sha...@ut... ber...@t-...
www: http://www.lysator.liu.se/~gz/bernhard