From the discussion of the phone Nokia 6303:

Maruska: people, please help me, I have a flv video on the comp, I copy the video to the phone, I put the 3gp format, and it still doesn't work.
Can this be corrected somehow?

Max: "I put the format 3gp"explain

Maruska: I press on the compe to rename the video and in the format I write 3GP, and then transfer the video to the phone

XD thank you very much 😉