half horizontal resolution file size problem

[Blackbat]

I've just encoded a PAL DV file using CCE with "half horizontal resolution" checked (and "dvd compliant" unchecked). I sort of assumed that the resulting mpeg2 file would be half the size than if I'd encoded at full 720x576 resolution, assuming the bitrates were similar. What seems to happen, though, is that the half D1 encoded file is the same size as the full D1 file.

Hmm. Just tried TMPG with the same result - output file size is the same regardless of whether target resolution is 720x576 or 352x576.

Can anyone explain this?

thanks,

Justin

[adam]

Resolution has no effect on filesize. Your filesize is soley determined by your bitrate.

filesize= bits per sec x number of secs.

If you want to set your output to a specific filesize use a bitrate calculator. I recommend FitCd.

[Blackbat]

Of course, how stupid of me.

I guess that I could drop the bitrate down if the resolution is less though, as fewer bits would be needed for a decent picture. SVCD, for instance, is pretty good with 2500kbps so 352x576 with, say, 4500kbps should be OK. I'll give it a try.

thanks,

Justin

[FredThompson]

Huh?

(480/360)*2500 = 3333 1/3, not 4500.

Maybe you should try 3500 as a more fair comparison.

[FredThompson]

Oh, yeah, half of 720 is 360, not 352. 352 is for VCD, not CVD.

[Blackbat]

Originally posted by FredThompson
Oh, yeah, half of 720 is 360, not 352. 352 is for VCD, not CVD.

352 (x576) can also be for DVD :-)

[FredThompson]

The first couple of lines talk about taking a D1 PAL source and reducing the horizontal resolution in half. That's 360. If 352 is legal, and I trust you on that, fine, it's compatible but it's not D2 or 1/2 of D1.

[FredThompson]

Have you shot PAL DV in America? I took NTSC DV under European florescent lights and the video pulses something fierce, especially when I kick the shutter speed up.

Makes sense when I think about it now but it sure wasn't something I expected.

[Blackbat]

I think you'll find that 352 is half D1. 360 is indeed 720/2, but not divisible by 16, so 352 is the nearest "legal" equivalent. Hence the use of 352x576 (or x480 for NTSC) in the DVD spec.

As for PAL DV in America, yes I have but only outdoors in sunny California :-)

[adam]

Originally posted by FredThompson
Oh, yeah, half of 720 is 360, not 352. 352 is for VCD, not CVD.

352 is used for vcd, cvd, and dvd.

VCD=352x240/288
CVD=352x480/576
DVD=352x240/288 (only with mpeg1 I believe), 352x480/576 and of course 720x480/576

[FredThompson]

Ah, yes, you're absolutely correct. I just looked at Aho's page and the MPEG specs because it dind't make any sense to me. I've been playing with CVD the past few days. Don't know how I got screwed up unless it had something to do with thinking about 1/2 the D1 resolution. It's also the DirecTV format, btw. (ok, well, with some added sync stuff 'cause both video and audio are VBR.)

Gad, that's embarassing. Where's my can of whiteout?

--

Yeah, weird thing that, maybe the sun is dual-format? Wonder if it does SECAM or that Brazilian (right? Brazil?) PAL variant.