Make torch_stft_fb.py encoder onnxable

[mpariente]

Ref #10
The fix was quite simple, but it always takes me time to find scriptable and onnxable tricks.

[mpariente]

And I cannot make the Decoder onnxable though.
If you want to give it a try @faroit, feel free!

[faroit]

Ref #10
The fix was quite simple, but it always takes me time to find scriptable and onnxable tricks.

cool, how did you find out that this causes problems?

[faroit]

@mpariente shall we add separate onnx tests for encoder and decoder, thus making at least something pass for this PR? I can then work on the decoder

[mpariente]

cool, how did you find out that this causes problems?

By elimination.

@mpariente shall we add separate onnx tests for encoder and decoder, thus making at least something pass for this PR? I can then work on the decoder

Yes, it would be nice to add tests.
I think they only work with nightly though, I'd have to check.
Do you want to implement them?

[faroit]

@mpariente good news, with your fix + torch 1.8.0 + setting opset to 11, both the decoder and encoder passes the onnx export.
We could go lower than opset 11 (which would allow better conversion to tensorflow) when the .squeeze(0) would be replaced...

UserWarning: This model contains a squeeze operation on dimension 0. If the model is intend
ed to be used with dynamic input shapes, please use opset version 11 to export the model.

I any case, i think separate tests should be added in a separate PR, i can do that. So I would suggest to merge this first

[mpariente]

I'd love tests, thanks !