We have managed to play audio files using SDL's Mix_PlayMusic function. The problem now we need to do some upsampling for one audio to match the other so that both have same duration. Any idea how to resolve this issue.
Do you want the pitch to warp with the speed?
Yes: Then you want time stretching.
This is simply interpolating / combining samples to generate the same overall waveform in a different number of samples. The obvious nearest neighbor approach will cause severe aliasing but technically works. To make it sound better one can use a higher order function like sinc interpolation.
No: Then you want time scaling.
This is usually boiling down the sound to a procedural / time domain representation, it is an active area of research and doesn't sound perfect. The common techniques are: