Audio sample rate adjustment for simple speed change (lossless)

[Noitarud]

I assume the audio is read at the sample rate speed, so if I somehow get the SR changed I should get a different audio playback speed (and this would be lossless), but with -c copy and -ar it appears to reencode (ignores -ar) and there is no speed change.
Here is the string I used:
"C:\Program Files\GPAC\ffmpeg" -i INPUT44100.mp3 -c copy -ar 22050 E:\slow.mp3

MP3: A little research gives me: sample rate is recorded on each frame, sample rates are specific steps, and this may only work per "version" (MPEG1 is 44.1/48/32k; V2 half of V1) if contents differ, such a conversion step (inside V1) may be expedient for some people, but not versitile enough for all (proper fractions of speed) even if between V1/2/2.5 were offered. ​http://mpgedit.org/mpgedit/mpeg_format/MP3Format.html
•Mp3 44100 to 48000 attempt same problem.

I can only see OGG, AIFF, WAV supports arbitrary values, so no good for me.

[Michael Koch]

This is the bug tracker. It's not the place for asking questions.