"ffmpeg -ss" supported formats for accurate seeking? mp3 does not appear to work, only .wav

Question

ffmpeg -ss 00:00:00 -i 'input.mp3' -to 00:25:00 -c copy output.mp3

I noticed while scripting that this particular script that it works for mp3 files but not for .wav files. What happens is it copies (strangely) to a 25 minute .mp3 file but it clips the audio at the end intrinsically. Seems to stretch the actual audio beyond the 25-minute boundary for some reason thus clipping happens. This doesn't happen with .wav files though. Searching through the man pages I came across this below:

-ss position (input/output) When used as an input option (before -i), seeks in this input file to position. Note that in most formats it is not possible to seek exactly, so ffmpeg will seek to the closest seek point before position. When transcoding and -accurate_seek is enabled (the default), this extra segment between the seek point and position will be decoded and discarded. When doing stream copy or when -noaccurate_seek is used, it will be preserved.

My question is, first, it appears that .mp3 is not a supported format that seeks exactly, but it appears that .wav files are supported given what happened. Is this the reason why it clipped the audio? Second, is there any documentation regarding supported formats that have 100% accurate -ss times? I can't find that in any of the man pages. Maybe documentation exists but if it does I'm guessing it should have been listed in that section. This is bad documentation on ffmpeg and should be updated! Vague information that's not helpful.

Answer 1

The only formats that are perfectly seekable, are non compressed formats. I.e. wav and pcm. All compressed formats encode into “frames” (because that’s how compression works). Using codec copy, you can only copy entire frames. Every codec uses a different number for samples per frame.