There are options to encode as interlaced for h264 (i.e. mp4), at least with ffmpeg. the -flags +ildct+ilme is the part of the command that does this. As an example, See this post
http://www.digitalfaq.com/forum/vide...html#post78883 Of course, with that, it then comes down to whether the video player you use will play it back nicely. I love the theory of not having to deinterlace the video, since the analog world is all interlaced. But sometimes the reality of the progressive/deinterlaced world we live in now makes it more difficult for PCs/tablets/phones to properly handle interlaced content. This option is not mentioned often, so I wanted to at least do that. It's something you'd have to experiment with to see whether it would work well for the use cases you plan to use it for.
If you are going to encode the file as deinterlaced, i.e the default for mp4, then it can be useful to do the deinterlacing on the AVI with QTGMC to either go from 30 frames per second (aka 60 fields interlaced) to 60 progressive frames per second. Or, if you find the video players or streaming setup you use don't play 60 frames per second very well, there is an FPSDivisor=2 option in QTGMC that will decimate back to 30 progressive frames per second for the final output. Or you can use the often mentioned SeparateFields().SelectEvery(4,0,3).Weave() to decimate the 60 fps back to 30 fps after running QTGMC.
Assuming capture at 720 x 480, and you want it to look 4 x 3 (640 x 480), you can either try the Spline36Resize option to go from 720 to 640 (or 704 to 640 if you use Avisynth to trim off the black vertical edges) or you can specify an aspect ratio option when you encode, with say ffmpeg using the sar options (see post referenced above). The options there are again sort of dependent on the players or setup you are using. If the players being used can properly take 720 x 480 or 704 x 480 file with a SAR flag that will make it display it in proper 4 x 3, then you could prefer that. However, if you have some players that don't honor that and those that are viewing care about it looking proper and not slightly stretched, then you can do the Spline36Resize to force the file to be 640 x 480 with a SAR of 1/1. That way, I think you would have less chance of a player incorrectly displaying the correct aspect ratio. DVD was much better about honoring the aspect ratio. But with H264, there are so many video players out there and not all of them handle simple standard features like aspect ratio (or deinterlacing, for that matter) as well.
