Any AVI has its own bitrate, which determines its size as function of its length.
A 700 MB AVI movie has
- very good bitrate if movie's length is 1h
- good bitrate if movie's length is 1.5h
- decent bitrate of its lengh is 2h
..and so on
When you convert to DVD movie an AVI, the DVD movie encoder has an option which detremines the DVD size as function of the movie's length.
To fix the most appropriate bitrate for an AVI --> DVD conversion you use the bitrate calculators, such as DVToolhttp://www.afterdawn.com/software/video_...ols/dv-tool.cfm which, you can check, tells you that if you encode a 120' movie to a M2V video using a video bitrate of 4723 kbps , once you insert in the authoring application an AC3 384 kbps audio stream, you fill more or exactly a DVD-R (4489 MB).
Once you know which is the mos proper bitrate to apply (the already mentioned 4723 kbps), you can encode CBR (any movie segment has a fixed bitrate of 4723 kbps) or VBR (the average bitrate is fixed, 4723 kbps, but the instantaneous bitrate is higher in fast movie's scenes and lesser in slower movie's scenes).
For instance, you could tell the encoder that the M2V video will have a bitrate:
2500 < bitrate < 6500 kbps; with average (bitrate) = 4723 kbps.
In these cases, the encoder will need more time to perform the so-called multi-pass analysis:
1st, .... (n-1) pass = scanning and
nth pass = encoding
This is the theory. In practice, if you use an AVI input (which has a smaller size than 4489 MB, generally its size is 700 MB or, only in particular 'lucky' cases, 1400 MB) the DVD quality is very often determined by the input AVIs quality, only.
