Very useful. Sometimes some flv conversion tools don’t include info that is vital for playback. In this case, the seekbar wouldn’t show up in the player until after playback finished. I’ll be testing to see if this resolves it but either way, this is good to know. The first hint was this post stating that the duration metadata probably wasn’t present in the file. A quick test with flvtool2 showed that indeed there was NO metadata. Using the command shown here, the data was added. I might either wrap this up in a python wrapper to batch a directory with it, or just bite the bullet and learn more shell programming to loop through all matching files in a directory.
 I guess looping in shell programming isn’t so bad:
ls -1 *.flv | while read file; do cat "$file" | flvtool2 -U stdin "$file" ; done
By default an flv movie doesn’t contain the duration metadata. Using the flvtool2 program it is injected like this into the movie file.
cat mymovie.flv | flvtool2 -U stdin mymovie.flv