Difference between revisions of "Video Playback Slightly Too Fast"

Revision as of 18:15, 11 March 2013

Best described by a user on AfterDawn forums: "Anyone notice this problem? It seems to be with some xvid or divx videos I've downloaded. The speed difference is so slight that you really can't tell until you watch the original and hear that the theme song is in a lower key and the voices are lower."

source: AfterDawn > Forums > Video playback problems > video plays slightly too fast

Files playing at 25fps but were filmed at 24fps will cause this problem. For European PAL TVs the film is simply sped up the 4.16%. The sound is also sped up and is a half-step too high. People are not encoding the files properly, and the difference is just too slight to notice.

Judging by the running times, I would guess the source was probably 24fps film. The 25 fps AVI probably came from a PAL DVD where the film is sped up to 25 fps. The 25 fps AVI retained that frame rate and probably has smooth, though slightly fast playback (compared to the original film).

Film can be shot at either 24fps or 25fps for PAL. There are two ways to transfer the film to tape.

Telecine A: 25 FPS frame-for-frame from the negative or workprint. Either film that originated at 24 FPS or 25 FPS can be transferred this way. If the film was shot at 25 FPS, there is no modification in the playrate. If the film was shot at 24 FPS, it is being played 4.166% faster.

Telecine B: 24 FPS adding a field at the 12th and 24th film frame (24 FPS film is cine-expanded to 25 frames). Film shot at 24 FPS is played at that rate with an additional frame generated in the telecine process so one second of film still plays at that duration on the PAL tape.