Hardware 3DS - SC DSTWO - iPlayer video encoding tips?

[velusip]

I've been tinkering with video encoding settings for the Supercard DSTWO iPlayer plugin (Version 1.1, rel 2010-11-17). I have stubled across some nuances.

First, it seems the filename must end with .avi to show up in the iPlayer file browser. However, the container type doesn't have to be avi. The lack of documentation has lead me to trial and error. I'm a novice at encoding video, so I'm sure there are some encoding tweaks I don't know that would help.

* When I try to encode a video with h264, the iPlayer hangs on "loading". e.g.

ffmpeg -i vid.mkv -vf "scale=256:-1" -map 0 -c:v libx264 -b:v 250k -c:a libmp3lame -b:a 192k out1.avi

* Trying h264rgb instead, iPlayer shows 1 grey frame and then finishes "playing" that video.
* Encoding mjpeg, xvid, and mpeg-4 all work perfectly, but there are issues with compression artefacts or huge file sizes. e.g.

Large files, but nice quality:
ffmpeg -i vid.mkv -vf "scale=256:-1" -qscale 2 out2.avi
 
Small files, but kinda ugly:
ffmpeg -i vid.mkv -vf "scale=256:-1" -map 0 -c:v libxvid -b:v 250k -c:a libmp3lame -b:a 192k out1.avi

I really wanted to use h264 because of the excellent quality and very small file size. At a resolution of 256*144 an hour of video with no artefacts at all is just over 100MiB. Does anyone have tips on encoding h264 for the iPlayer plugin?