[mythtv-users] IVTV Bitrate & Resolution

Scott Alfter mythtv at salfter.dyndns.org
Sat Mar 24 20:27:38 UTC 2007

Ma Begaj wrote:
> 720x480 ?
> that's not 4:3 ...   720x540 would be 4:3 ...

You definitely don't want to use 720x540, as there are only 480 scanlines in
NTSC video.

Encoding resolution and aspect ratio are really somewhat unrelated concepts.
If you're dealing with a file format (such as an MPEG-2 program stream or an
MPEG-4 container with H.264 video) that stores info on the video's aspect
ratio, you can encode video at whatever horizontal resolution you want.  On
playback, it'll be scaled appropriately to restore the correct proportions.  If
you have 4:3 video encoded at 480x480, it'll be scaled to 640x480, 1024x768, or
whatever on playback.  16:9 video can also be encoded at 480x480 (and on DVDs,
it's encoded at 720x480).  For playback, it could be scaled to 852x480,
1280x720, etc.

Lame formats (such as DivX AVIs) don't provide for including aspect-ratio
information in the file, so they need to be encoded in a square-pixel format
(like 852x480) that wastes bandwidth without providing a visible quality
improvement.  Basically, you have to scale the video before it's encoded (and
possibly scale it again on playback).  If aspect ratio is stored with the
video, it only needs to be scaled once, on playback.

 / v \ Scott Alfter
(IIGS( http://alfter.us/            Top-posting!
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