I need a command line utility for Linux which can change the tempo of an audio track at a non-constant rate: for example, the tempo rate might be 100% right at the beginning of the output track and 150% at its end, and would grow between the two points linearly. I only need tempo changes, which means that pitch should not be affected. I expect the application to be capable of changing the tempo linearly, any additional modes are, of course, welcome. I expect the application to support “wav” audio format, any other common audio formats, like “mp3” or “ogg”, are fine too.
I've considered “sox”, “rubberband”, “ffmpeg”, and “soundstretch”; all the four applications only seem to change tempo by a fixed amount. I haven't considered any GUI applications with no CLI counterparts, because I would like to use the utility in Bash-scripts. I have considered splitting the audio into multiple small fragments and changing the tempo of each one, but I'm not inclined to use this method because, given the amount of material I expect to work with, this will either take too much time or produce unsatisfactory sound quality.