As sometimes we receive reports about not streaming well videos, here's short explanation what is most possible reason:

Each video played by any flash payer should have information about keyframes.

1. FLV videos

If FLV video not "keyframed" - it still should play fine with PROGRESSIVE streaming method.
But when you try to make use of http streaming (streaming mods for lighttpd, nginx or Apache), when you try to jump to new position player will not be able to calculate jump position because of missing information about keyframes. This concerns every flash player that supports http streaming.

Usually each video script during conversion of uploaded video makes use of tools like FLVTool2 or Yamdi to insert some additional information (about keyframes, duration, size, author ) into final FLV video.
If video uploaded in other than standard upload way (eg. using FTP transport) final FLV video may miss all those information.
Also if uploaded video is of FLV format and video codec is other than Soerensen, tools like FLVTool2 may fail with inserting keyframes info into final video.
Another issue can be very long video. In such case FLVTool2 may also fail and suggested is to use Yamdi tool then.
If none of methods will help - last chance is to use desktop software like free FLVMDI from http://www.buraks.com/flvmdi/ before you upload video to your server.

2. MP4 videos

Standard MP4 video stores meta data in position that cannot be found by any flash player.
This can be solved with small desktop application, that moves MOOV atoms to the beginning of MP4 file.
You can DOWNLOAD this tool free from our server and use for MP4, also in batch mode.

MP4 video with h246 video codec usually doesn't require any additional efforts. Eg. downloaded youtube MP4 video is fine for any type of streaming.