Resolution rule?

[NotSoEasy]

Is it really necessary to downsize resolution?
I mean, going from 720 x 480 source for example, to anything smaller seems like a bad thing when converting to say XviD.
Would you not be loosing pixels at this point? What about viewing this on a TV which is much larger than your PC monitor.Would it not look pixelated?

Reason I ask is I see so many conversions that are so small ( and sometimes wrong ) it makes you wonder why.Your trying to make a good backup, only in a different format.

[guns1inger]

The first Divx enabled players were only able to read Divx files from CDs, so a movie had to be able to be backed up to 700 MB. Keeping it full-D1 resolution and compressing it to 700 MB killed quality and defeated the purpose. Even today, many have a 1 GB limit (i.e. wont play back single files larger than 1 GB), so reducing resolution is a fair compromise in order to keep bitrate high enough. High res + low bitrate = crap. Lower res + higher bitrate = acceptable viewing in most cases.

It is really a technical limitation of the playback hardware we currently have.

[FulciLives]

The "best" XviD resolution to use is 640x480 as that is the same as the DVD resolution of 720x480 ... the difference in width is because MPEG-4 (what XivD really is) uses square pixels whereas DVD does not use square pixels.

It's also common to cut the black on a widescreen movie. So for instance a NTSC DVD with an aspect ratio of 2.35:1 would be 640x272 for the XviD version. Also it is common to switch from 16x9 anamorphic on the DVD to 4:3 widescreen. So for instance a NTSC DVD with an aspect ratio of 2.35:1 that is also 16x9 would be 720x360 when you cut the black but again it becomes 640x272 for the XviD version.

As for the "best" resolutioin ... some people use a smaller resolution because there often times is not enough bitrate to go the full width of 640 pixels when converting a DVD down to the size of a single CD (700MB). If creating your own DVD to XviD copies I would make the size 2 CD (1400MB) as that will give more bitrate meaning you can go for the 640 width and still get very good quality.

- John "FulciLives" Coleman

[NotSoEasy]

See, thats what I was thinking, but then when I looked at some resolutions, they just seemed off to me.Even though they seemed to follow this rule of thumb.
For example, I was watching a 640x272 XviD and it just seemed smashed to me.Telling DivX player to use 640x306-320 made it look proper.So that tells me the AR is going to be off and what will it then look like on my TV if I were to re-encode it to that resolution?

As for bitrate, that has yet to sink in here in this head
Im learning though!

So lets see.What we do is take 720 and devide by the AR....

720 / 2.35 ( 2.35:1 ) gives us 306 so = 720x306
720 / 1.85 ( 1.85:1 ) gives us 389 so = 720x390
720 / 16:9 or 1.78 ( 1.78:1 ) gives us 404 so = 720x404

Then there is this one
640 / 4:3 or 1.33 ( 1.33:1 ) gives us 480 so = 640x480
I am assuming that fullscreen 4:3 has a resolution width of 640 rather than the 720 which belongs to widescreen?

[celtic_druid]

XviD is MPEG-4 which supports non square pixels. And the first 700MB encodes would have been well before hardware players. I know mine were. DVD burners just didn't exist and then when they did, they were slow and expensive. Also the limit is 2GB's since most players don't like UDF.

I agree, if you can encode at full resolution with the PAR set correctly so that it resizes on playback.

You should also crop black borders and use a mod16 resolution.