I have a lot of FLVs that are unseekable. I have tried a number of converters, because that is all that I have read about for solving the problem, however the only one that I have found that works for me is HandBrake. The problem with it is that the only output options are for either MKV or MP4. Since I have had some problems with MKVs in the past, I am using the latter. The reason that is a problem is because the converted MP4 is twice as large as the original FLV, and I see no difference in either audio or video quality. Is there not a way to make a FLV seekable and keep the FLV format so that the size remains the same?