Downloads - bigger file means better AV quality

[Njr Scrawl]

Being new to downloads, does more megabytes (bigger file) of an episode usually mean that the quality of that episode would be better than the same episode with less MB/smaller file?

[TalonG4]

Sometimes but not always, it depends how good the encoder is and also which codec they are using. For example h.264 video codec looks better than XviD but ideally should be a smaller file size.

[TAS]

Being new to downloads, does more megabytes (bigger file) of an episode usually mean that the quality of that episode would be better than the same episode with less MB/smaller file?
If everything else is the same yes, but that is not often the case.
Codec - An MPG2 file will be much bigger then an XVID file.
Skill of the encoder - Toei's Slam Dunk downloads are 339 MB, very large for a single episode. I've seen similar material with better quality at half the size.

[bayoab]

Assuming a competent person doing the encoding and a proper codec (DivX, xvid, x.264, etc), the size vs perceived quality function follows a logistic curve (http://en.wikipedia.org/wiki/Logistic_curve). There is eventually a point where you can make the file 100mb larger and it won't look any better. This point is typically around 250mb for DVD resolution with the above named codecs, but depends on the series, file resolution, and many other things.

[Quarkboy]

Let me be overly specific, in case anyone is interested.

As a reference, let's review the DVD standard:

At a semi standard 640x480 resolution (often called SD, somewhat erroneously) and 23.976 fps or 29.97 fps, DVD video video has bitrates of around 6-8 Mb/s (megabits/s if you want megabytes=MB, divide by 8).
A standard episode of anime is 22 minutes = 1.2 GB per episode. (This can very by quite a lot, depending on how many episodes you need to cram onto a DVD, etc...)

The next "generation" of codecs, are divx, xvid, and wmv... (technically wmv 7 only, as wmv 9 is considered a rival to AVC, although IMO it's not much better than xvid)...
As a rule of thumb, these codecs are about 6 times more efficient than mpeg 2 based codecs at very low bitrates (<1 Mb/s), and about 2 times more efficient at very high bitrates (> 5Mb/s).
So we would expect a "DVD" quality at around 2-3 Mb/s, which works out to filesizes of ~400 MB. As a comparison, Toei animation's download to own files are wmv encoded at 2 Mb/s (although they look like crap, however that has to do with how they are filtered and not the codec efficiency).

Then, the most recent generation of codecs, h.264 aka mpeg-4 AVC and WMV 9 (in my opinion WMV9 fails significantly compared to AVC, but that's simply because it's not an open standard and the only encoder that's available is from microsoft) have, as a rule of thumb, is 10 times more efficient than mpeg 2 at low bitrates (<1 Mb/s) and nearly 20 times more efficient at super low bitrates (<400 Kb/s), and 3-4 times more efficient at very high bitrates (>5 Mb/s)

You can easily get DVD quality using bitrates of 1.5-2 Mb/s with h.264. And if you are willing to lose a little bit of quality (mainly with some extra smoothing), 500 Kb/s encodes look pretty nice.
As an example of super low bitrate h.264, Youtube's "high quality" streams are very low bitrate h.264, which look pretty decent.

So that's basically all the info you'd need to enable you to roughly compare filesizes, even if the files are encoded using different standards (assuming they're the same resolution, anyway).