On 25 Nov 2003, Florin Andrei wrote:
> Conditions:
> My source is a cheap CCD, not too bad, pretty good detail, excellent
> chroma, some mild noise when in the dark but otherwise it's clean.
>
> Goals:
> I want to put my movies on DVDs with the highest quality that's
> achievable with the mpeg2enc encoder.
> Also i want to obtain the highest portability and compatibility
> especially w.r.t. standalone players.
>
> Now the questions:
>
> How often is actually needed -s? What do i loose if i don't use it?
DVDs require it - "-f 8" sets it automatically for you.
> Any side-effects of -c?
Minimal increase in filesize (few tenths of a percent) due to
very slight decrease in compression efficiency. For editing
purposes -c is very useful (and _required_ for multi angle DVDs).
> Is it a good choice to use -g 6 -G 18?
> Any possible side-effects of doing that?
> In general, when would you recommend to tweak -g -G?
High motion videos might benefit from '-g' being decreased - in fact
you could set that to 1 (if you're using the cvs version of mpeg2enc
or at least the current release candidate). Lowering -g will increase
the size of the file because more I frames will be generated.
-G is set correctly for the standards - don't raise it unless you're
only playing back on a computer (or a *very* forgiving settop box).
> Did anyone actually encounter a set-top DVD player that gets upset by -R
> 0?
Nope - and you won't. B frames are an additional feature of the
higher levels of the MPEG standards - they're not required.
> What are the default values of -4 and -2? (the equivalent of not using
> them at all)
I use -4 2 -2 1. Dropping -4 from 2 to 1 increases the encoding
time by a lot (30 - 40%) for a nominal (couple percent at best)
decrease in average bitrate.
> -E -20 corresponds to what kind of quality? VHS-like? Broadcast-like?
It's not that simple... But you knew that ;) -20 is moderately
aggressive, and I've not tried that setting, but it most definitely
would not degrade things to VHS levels.
Since you're not overly concerned about bitrate/filesize I'd suggest
a modest -E setting.
> What's the _visual_ difference (the result) between positive and
> negative values? When would you recommend either side?
Don't know that - I just started with - values and left it there ;)
> What -E value would you recommend to start experimenting with in my
> case?
-10 is a good non-aggressive/mild setting (i've seen good results
with -5 to -8).
> Could you please comment on this combination of parameters? Anything
> that doesn't make sense? Any contradictory parameters?
>
> -b 9800 -E -15 -q 6 -R 0 -s -c -I 1 -g 6 -G 18 -4 2 -2 1 -K tmpgenc -N 1
9800 is too high. Some standalone players can not handle the maximum.
For portability you'll really want to back off to something like 8500.
Skip the '-s' - it's redundant. The "-I 1" is the default so there's
no need for that but I can understand having explicit reminders in the
command line. Just take the default for -G (mpeg2enc knows the
NTSC and PAL limits for the max GOP size so why second guess it?) and
leave that out. The minimum is up to you
For maximum quality use just I frames "-g 1 -G 1" :-) The filesize
will be large but the encoding will be very very fast.
Steven Schultz
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