I am working on an mp3 decoder, the formula to determine the length, in bytes, of an mp3 frame is
FrameSize = 144 * BitRate / (SampleRate + Padding)
I can't find anywhere that explains what the '144' represents.
Does anyone know?
The 144 represents total bytes-per-frame.
MP3 files are generally encoded as MPEG-1 Layer 3.
There are 1152 samples per frame in type Layer 3.
1152 samples / 8 bits-per-byte = 144 bytes total.
Taking the formula for frame size (in bytes):
FrameSize = 144 * BitRate / (SampleRate + Padding)
We can see (for MP3 with 192 bitrate @ 44.1 khz):
144 * 192 / (44.1 + 0) = 626 bytes per audio frame (fraction parts are ignored).