# Framerate conversion

1500 frames
60 secs / 60

### Conversion 'conform': 25 → 23.976fps

##### Definition
The total # of frames stays the same
##### Speed
video is slowed down from 25 to 23.976 fps
##### Audio
As a result, the audio will sound lower
##### Correct audio
pitch up by +4.271% (0.724 semitones)
##### Convert video
ffmpeg -i [input] -r 23.976 -filter:v "setpts=1.0427*PTS" -y [output]
##### Convert audio
sox [input] [output] tempo 0.959
ffmpeg -i [input] -filter:a "atempo=0.959" -vn [output]
##### Duration: time
1500 frames / 23.976 fps

### Conversion 'interpolate': 25 → 23.976fps

##### Definition
The total duration stays the same
##### New length
60 seconds * 23.976 fps
##### Naive conversion
drop a frame every
##### Convert video
ffmpeg -i [input] -r 23.976 -y [output]
##### Convert audio
audio stays exactly the same

### Explanation

• Calculate # frames from time duration and vice versa. e.g. 93 sec @ 24fps = 2232 frames
• Calculate how audio and video should be manipulated to change from one framerate to another, using sox and/or ffmpeg
• When is this necessary? If you have a video that was recorded in 25fps(PAL) or 30fps(NTSC), and you want to show it on a cinema screen: you have to convert the framerate to 24 fps.