I have video playback working perfectly but it wasn't the case to start with: approximately once per second there was a discontinuity in a frame. I found such a frame using my rewind/fast forward buttons and it was immediately obvious that some page boundary (actually 4MByte) was being crossed which caused a line and a half to be lost while the card sorted itself out internally.
I feared this sort of thing might happen. The fix is straightforward though - don't cross 4MByte boundaries within a picture. I've gone further than that and ensured that no field crosses a 256 sector boundary. I did this because I can't predict the internal implementation of CF cards and so my feeling is that as few as possible boundaries should be crossed within the video, even if this impacts on total playing time (my 8GByte CF card can still store over 20min of 405 lines).
I'm VERY happy with the quality of the playback - much better than I expected with a resistor video DAC (the artifacts I had before turned out to be caused by the JPEG compression of the photo I downloaded!)
Next step: get audio working, and despite all the help Kat has given that has enabled me to get the video working I'm going to be cheeky and ask for help on the audio side
Basically, I'm going to do a run of ffmpeg prior to the video conversion run (involving reinterlace.c) to generate a raw audio file. It won't be too big - audio is 1% the size of the video.
I need ffmpeg to produce a raw file of monophonic 16 bit samples at 40500 samples per second. Is that possible? I'll settle for stereo and convert to mono in reinterlace.c