Checking Metadata or Moov Atom Location
In order for Mp4 or M4v files to play while they are being progressively loading into a player the metadata or moov atom that contains the play and stop controls needs to be moved to the front of the file.
The moov atom that is a part of the metadata for mp4 and m4v files is also known as the index of the file because it contains all of the information about the file that is read by any video players. Video encoders will often automatically move the metadata to the front of video files to make them web ready. Sometimes this is not the case. If you want to check the location of the moov atom you can use a simple hex editor and open your video files.
Once you have the file open simply search for "moov" and you should be able to tell the location based upon the line it is located on within the file.
If the metadata is located at the back of the file, then simply move it to the front of the file.
If you are using Windows use RNDWare MetaData Mover or MP4 FastStart.
If you are using a Mac, you can use Adobe Air (as an installation platform) and the QT Index Swapper to fix the metadata on your mp4 files.
You can get adobe air here:
http://renaun.com/air/QTIndexSwapper.air
Adobe Air is the platform that the program runs on. You have to first download and install Adobe Air. After that finishes, download and install QTIndexSwapper. Run QTIndexSwapper and choose the file you want to fix the metadata issue on.
Quicktime pro users can move the metadata by opening the file and choosing File->Export->Options then selecting Fast Start before re-saving the file.