Bitrate calculator in ffmpegx, a setting or what?

[Kave]

First, thank you Major for making such a nice GUI to the various mpeg tools. I have find it much easier to use then the others.
I just wonder if the bitrate calculator is just a calculator, or if it sets the actual bitrate in the final mpeg?
I use it this way:
1. Point out where the vob file is ( from 0Sex).
2. Point out where to save the result.
3. Use quick preset > MOV, VOB or Divx > MPEG2 SVCD PAL
4. fill in how large the movie is,in minutes, and how many CD's I like to have it fit into, in my case 120 mins of video, 3 cd's
5. Hit "Split in 3 chunks" in the Tools tab
6. Hit encode.
This will result in 3 mpeg files which is 711MB each, and SVCD images.
I have tried to manually lower the bitrate in the calculator without ending up with smaller files, howcome? Is there any other setting to make the resulting files actually fit an amount of cd's, ie making them smaller?

[major]

The calculator sets the bitrate, but SVCD has always bitrate forced to 2500, conforming to the standard, no matter what you enter. If you want to lower the bitrate, set MPEG-2 profile (in the mpeg-2 options tab) to "XSVCD".

[promoter]

I'm testing whether setting ffmpegX 0.0.4d's "MPEG-2 constant quality (no bitrate limit)" will produce a higher quality NTSC SVCD from an .MOV source file than the SVCD preset. I understand that the SVCD preset will override any customization unless the XSVCD or Generic MPEG-2 profiles are used, so after reading Major's response above I launched ffmpegX with the following settings:

-VIDEO Tab: Video Codec "MPEG-2 [.MPG]," Video bitrate 2500, 30 minutes, Keep in 1 CDs of 80min mode-2, video size 640x352, Autosize 4:3, Framerate NTSC (29.97)
-MPEG-2 Tab: "XSVCD" profile, "Constant quality (no bit rate limit)," Non-interlaced, VBV size 230kb, with Bicubic Scaling, Altivec (I'm on a G4), and Denoise encoding options.
-TOOLS Tab: "Author as SVCD (XA .img)" only.

Upon clicking "Encode," the Terminal window gives me the following error:

"**ERROR: [mpeg2enc] Generic format - must specify bit-rate!"

I've typed 2500, 2600, and other numbers in the Calculator's Video Bitrate box, but still get this error. This happens even if I let the calculator populate the Video Bitrate by pressing one of the "Calculate" buttons. When I press the left Calculate button, it fills the field with 3469; the right one, 2440. Using the "Generic MPEG-2" profile instead of XSVCD produces the same error. It seems I'm providing a bit rate in the right place, but mpeg2enc still complains. What am I doing wrong? Also, does the "Constant quality (no bit rate limit)" cause mpeg2enc to use VBR?

[major]

video size 640x352, Autosize 4:3

These values should not be used. To make a XSVCD first select the SVCD preset, then change profile to XSVCD and change the bitrate, as the image size should be SVCD compliant if you want playback on a DVD player.

"**ERROR: [mpeg2enc] Generic format - must specify bit-rate!"

You found a bug. Thank you. I'll fix it in 0.0.4e.

Also, does the "Constant quality (no bit rate limit)" cause mpeg2enc to use VBR?

Right now VBR is always used. The bitrate can go from a lower limit set by the q factor, to an upper limit set by the bitrate value. I'll implement the CBR checkbox later. "Constant quality" means there is no upper limit to the bitrate, this could not work on DVD players not being able to play SVCD with bitrate higher than 2500.

[promoter]

Major,

Thanks for the help. From another thread, I know you're considering putting together a FAQ, guide, or manual. It's been a bit frustrating, but acceptable given that ffmpegX is a work in progress & how much it automates the process. I'm slowly getting the hang of ffmpegX through posts like this.

"Constant quality" means there is no upper limit to the bitrate, this could not work on DVD players not being able to play SVCD with bitrate higher than 2500.

That explains the mess I saw on my DVD player when I checked this box, regardless of the bit rate I set in the Calculator. So in a nutshell, since ffmpegX is already using VBR, I just need to experiment with the highest bit rate my DVD player will handle, since it chokes when I check the "Constant Quality" box. Thanks for your help!

[promoter]

OK, I'm being a bad boy & staying up way too late testing Major's advice. But this is getting pretty interesting. My DVD player can handle 4000, 5000, & 6000 kbit/s, though 6000 gets a bit jerky & the sound starts cutting in & out.

I think the garbled screen I referred to in my last post was due to the incorrectly set video resolution rather than a too-high bit rate. So now, I'm really excited to see Major fix the "**ERROR: [mpeg2enc] Generic format - must specify bit-rate!" bug, because I want to try that "Constant Quality" checkbox. Thanks again for your hard work at making ffmpegX available, and for the great advice, Major!