Feature needed to prevent user error when sample rates or channels vary

[rbracco]

This is a very common error when making a batch:
RuntimeError: invalid argument 0: Sizes of tensors must match except in dimension 0. Got 1 and 2 in dimension 1

and is a result of doing one of the following 4 things.

1. mixing mono and stereo or...
2. different sample rates or...
3. you forgot to crop to same width or...
4. you cropped to same width but did a transform after that altered width somehow

It would be very nice if we added warnings to alert users to presence of multiple sample rates (Resample required) or varying # of channels (downmix required), or neither (crop required).

[PranY]

I recently faced 1 and 2 and eventually solved 1 by writing a custom method and 2 by using a custom sox hack. I didn't know about DownminToMono and Resample before.

I think the way I traced the error is a good fix to the above situation. I can write a method verify_pipeline() that takes the pipeline of transformations or tfms in-general, loop through transform and tells where exactly the problem lies.

If this approach makes sense to you then please give me a thumbs-up and I'll write, test and send a PR.

[mogwai]

That could be interesting, I was thinking of writing a verify pipeline for another features that we're still missing from the previous version. I think that this may be useful so please feel free to open PR and we can continue the discussion there. Thanks again for your help!