[MPlayer-users] -ss Does it work? Also bpp. Bunkus explain maybe?

[D Richard Felker III]

On Sun, Jan 12, 2003 at 09:17:52PM -0500, Geoffrey Trexler wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> Does the start position (-ss) work? I'll show you the options I'm using.
> 
> cat *.vob | nice -+19 mencoder -aid 128 -oac mp3lame -lameopts
> vbr=3:br=128 -ofps 23.976 -ovc lavc -lavcopts
> vcodec=mpeg4:vhq:vbitrate=1608:vqmin=2:vqmax=31:vpass=1 -vop
> scale=528:-2 -ss 00:00:21 -endpos 01:55:50 -; cat *.vob | nice -+19
> mencoder -aid 128 -oac mp3lame -lameopts vbr=3:br=128 -ofps 23.976
> -ovc lavc -lavcopts
> vcodec=mpeg4:vhq:vbitrate=1608:vqmin=2:vqmax=31:vpass=2 -vop
> scale=528:-2 -ss 00:00:21 -endpos 01:55:50 -

Of course -ss doesn't work on non-seekable streams such as pipes. WHY
ON EARTH are you copying vob files and then cating them to mencoder to
encode?? PLEASE EVERYONE! There's a reason mplayer/mencoder have a
-dvd option. It works MUCH better than trying to play vob files.

Also if you simply CAN'T use -dvd with mencoder (for example if the
DVD drive is on a different computer, still DO NOT COPY THE VOBS!
Instead use mplayer -dumpstream to get the entire DVD as one decrypted
file and encode from it.

> Ok about the bits per pixel. I put this in:  perl ../../calcbpp.pl 720x466 1.78 1608 29.97
> 
> Prescaled picture: 1025x466, AR 2.20
> 720x320, diff   7, new AR 2.25, AR error 2.21% scale=720:320 bpp: 0.233
> 704x320, diff   0, new AR 2.20, AR error 0.01% scale=704:320 bpp: 0.238
> 688x320, diff  -7, new AR 2.15, AR error 2.33% scale=688:320 bpp: 0.244
> 672x304, diff   1, new AR 2.21, AR error 0.47% scale=672:304 bpp: 0.263
> 656x304, diff  -6, new AR 2.16, AR error 1.96% scale=656:304 bpp: 0.269
> 640x288, diff   3, new AR 2.22, AR error 0.99% scale=640:288 bpp: 0.291
> 624x288, diff  -4, new AR 2.17, AR error 1.55% scale=624:288 bpp: 0.299
> 608x272, diff   4, new AR 2.24, AR error 1.57% scale=608:272 bpp: 0.324
> 592x272, diff  -3, new AR 2.18, AR error 1.09% scale=592:272 bpp: 0.333
> 576x256, diff   6, new AR 2.25, AR error 2.21% scale=576:256 bpp: 0.364
> 560x256, diff  -1, new AR 2.19, AR error 0.58% scale=560:256 bpp: 0.374
> 544x240, diff   7, new AR 2.27, AR error 2.93% scale=544:240 bpp: 0.411
> 528x240, diff   0, new AR 2.20, AR error 0.01% scale=528:240 bpp: 0.423
> 512x240, diff  -7, new AR 2.13, AR error 3.13% scale=512:240 bpp: 0.437
> 496x224, diff   1, new AR 2.21, AR error 0.64% scale=496:224 bpp: 0.483
> 480x224, diff  -6, new AR 2.14, AR error 2.67% scale=480:224 bpp: 0.499
> 464x208, diff   3, new AR 2.23, AR error 1.37% scale=464:208 bpp: 0.556
> 448x208, diff  -4, new AR 2.15, AR error 2.15% scale=448:208 bpp: 0.576
> 432x192, diff   4, new AR 2.25, AR error 2.21% scale=432:192 bpp: 0.647
> 416x192, diff  -3, new AR 2.17, AR error 1.55% scale=416:192 bpp: 0.672
> 400x176, diff   6, new AR 2.27, AR error 3.19% scale=400:176 bpp: 0.762
> 384x176, diff  -1, new AR 2.18, AR error 0.84% scale=384:176 bpp: 0.794
> 368x160, diff   7, new AR 2.30, AR error 4.34% scale=368:160 bpp: 0.911
> 352x160, diff   0, new AR 2.20, AR error 0.01% scale=352:160 bpp: 0.953
> 336x160, diff  -7, new AR 2.10, AR error 4.77% scale=336:160 bpp: 0.998
> 320x144, diff   1, new AR 2.22, AR error 0.99% scale=320:144 bpp: 1.164
> 
> I don't really understand what all this means. For example diff -4
> ???, and AR error ??? Could someone explain this in detail to me?

AR = aspect ratio, AR error = how much the aspect ratio is off by if
you use those dimensions. You can't get the exact aspect you want
unless you make width and height not divisible by 16, but that will
lower quality. Also these numbers look a bit fishy...are you sure
you're using the script right?

> I'm trying to encode a good DVD Quality Spiderman onto two 700MB
> CD's. That's my goal. It looks really nice in the low motion scenes
> with the settings I have above, however in the high motion scenes it
> doesn't look that great. BTW the movie is 121 minutes long, but I'm
> going to cut some of it, which is why I'm trying to get the -ss to
> work. So it should turn out to be about 115 minutes long. Maybe this
> will help in your calculations.

With the bitrate you have it should look nearly identical to the DVD.
However you're not cropping the black borders it seems, so that will
lower quality quite a bit! Use -vop cropdetect with mplayer first to
figure out crop values, then tighten them in a little bit to make sure
you get rid of all the border.

Also read the docs and the encoding tips file.

Rich