yet another noob conversion question

[perry2]

Sorry if this question has been asked a zillion times, didnt see anything exactly like it. So here goes...
I have a movie file and Gspot tells me this about it:
it is an Xvid encoded file, runtime 1 hour 17 min 12 sec, video is 464x352 @ 29.97 fps and an 1149 kbs rate. The audio is mp3 @ 108 kbs and 48khz.
I want to run it through Tmpenc to get elementary streams that I can author to DVD. At first glance one might think that by doubling (sorta) the vid resolution to 720x480 that I would end up with a file(s) approximately twice the size of the original (700 meg). Not so, Tmpegenc tells me I'm going to end up with files(s) of over 4 gig! Obviously I havent set up Tmpgenc properly. I told it to encode the file with an audio bitrate of 112kbs and a video bitrate of 2000kbs. If I make the video bitrate lower, it forces the video to half D1. What am I doing wrong? Im also confused about the video bitrate reported by Gspot, is this supposed to be a constant bitrate or the average of a variable bitrate? I assumed that I should set up Tmpegenc with the same bitrates reported by Gspot and that they were constant rates. Like I said though I couldnt go below 2000 kbs for the video in Tmpegenc.
thanks for any tips

[whitejremiah]

Your problem may be in the audio, not the video.....i've had tmpgenc spit out COMPLETELY wrong filesizes for audio if the source is VBR.....perhaps you should take the audio and convert it to wav first......this may fix it...

[ZippyP.]

Some points to ponder....

Resolution does not affect file size, only running time and bitrate.

The bitrate for an xvid and mpeg are not directly related as they are different compression types. Generally Mpeg requires much higher rates.

You should not upsize when converting, in this case you should go for 1/2 dvd - 352X480.

A 352X480 mpeg needs at least 2000 kbps, 3000 is even better.

Using a wav audio source will avoid problems.

112 kbps audio will sound crappy, 192 is much better. Why skimp?

Gspot will report an average bitrate.

[jagabo]

There's nothing wrong with upsizing video. If you downsize it for DVD your DVD player is going to upsize it again for display. So in the end it's going to be upsized -- the questions are which upsizer is better (the software upsizing from 464 to 720, or the DVD player's upsizing to the equivalent size -- after losing 25 percent of the resolution from downsizing from 464 to 352), and is it worth the extra bitrate the larger frame size is going to require. And of course, don't expect the picture quality to improve either way.

TMPGEnc's resizer is adequate but not the best. Since your video is only 77 minutes long you shouldn't have any problem with 720x480. Just select an appropriate bitrate -- around 6000 kbps for a 77 minute movie will fill a 4.3 GB DVD.

If you want an even better resizing (up or down), use AVISynth's LanczosResize or Lanczos4Resize. But that will require that you install AVISynth and learn how to use it...