Fix vad to return zero output for zero input

[wasd96040501]

fix #3668 Return empty result when not has_triggered. Zeroed wav audio added to unit test.

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:x: 13 New Failures, 2 Unrelated Failures

As of commit 451ee170d0ea20573de574472f497eb5ee19d8af with merge base 36f5010b9b61092cf03d2e5f39708b1ec2f0caeb ():

NEW FAILURES - The following jobs have failed:

* [Build Linux Conda / pytorch/audio / conda-py3_8-cpu](https://hud.pytorch.org/pr/pytorch/audio/3685#18487811893) ([gh](https://github.com/pytorch/audio/actions/runs/6800069780/job/18487811893)) * [Build Linux Conda / pytorch/audio / conda-py3_8-cuda11_8](https://hud.pytorch.org/pr/pytorch/audio/3685#18487812287) ([gh](https://github.com/pytorch/audio/actions/runs/6800069780/job/18487812287)) * [Build Linux Conda / pytorch/audio / conda-py3_8-cuda12_1](https://hud.pytorch.org/pr/pytorch/audio/3685#18487812831) ([gh](https://github.com/pytorch/audio/actions/runs/6800069780/job/18487812831)) * [Build M1 Conda / pytorch/audio / conda-py3_8-cpu](https://hud.pytorch.org/pr/pytorch/audio/3685#18487812288) ([gh](https://github.com/pytorch/audio/actions/runs/6800069759/job/18487812288)) * [Build MacOS Conda / pytorch/audio / conda-py3_8-cpu](https://hud.pytorch.org/pr/pytorch/audio/3685#18487815824) ([gh](https://github.com/pytorch/audio/actions/runs/6800069763/job/18487815824)) * [Build Windows Conda / pytorch/audio / conda-py3_8-cpu](https://hud.pytorch.org/pr/pytorch/audio/3685#18487812290) ([gh](https://github.com/pytorch/audio/actions/runs/6800069782/job/18487812290)) * [Build Windows Conda / pytorch/audio / conda-py3_8-cuda12_1](https://hud.pytorch.org/pr/pytorch/audio/3685#18487813356) ([gh](https://github.com/pytorch/audio/actions/runs/6800069782/job/18487813356)) * [Unit-tests on Linux CPU / tests (3.10) / linux-job](https://hud.pytorch.org/pr/pytorch/audio/3685#18529504747) ([gh](https://github.com/pytorch/audio/actions/runs/6800069756/job/18529504747)) * [Unit-tests on Linux CPU / tests (3.8) / linux-job](https://hud.pytorch.org/pr/pytorch/audio/3685#18529504078) ([gh](https://github.com/pytorch/audio/actions/runs/6800069756/job/18529504078)) * [Unit-tests on Linux CPU / tests (3.9) / linux-job](https://hud.pytorch.org/pr/pytorch/audio/3685#18529504426) ([gh](https://github.com/pytorch/audio/actions/runs/6800069756/job/18529504426)) * [Unit-tests on Linux GPU / tests (3.10, 11.8) / linux-job](https://hud.pytorch.org/pr/pytorch/audio/3685#18529451810) ([gh](https://github.com/pytorch/audio/actions/runs/6800069800/job/18529451810)) * [Unit-tests on Linux GPU / tests (3.8, 11.8) / linux-job](https://hud.pytorch.org/pr/pytorch/audio/3685#18529452140) ([gh](https://github.com/pytorch/audio/actions/runs/6800069800/job/18529452140)) * [Unit-tests on Linux GPU / tests (3.9, 11.8) / linux-job](https://hud.pytorch.org/pr/pytorch/audio/3685#18529452492) ([gh](https://github.com/pytorch/audio/actions/runs/6800069800/job/18529452492))

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

* [Build Windows Conda / pytorch/audio / conda-py3_8-cuda11_8](https://hud.pytorch.org/pr/pytorch/audio/3685#18487812850) ([gh](https://github.com/pytorch/audio/actions/runs/6800069782/job/18487812850)) * [Unit-tests on Macos CPU / tests / macos-job](https://hud.pytorch.org/pr/pytorch/audio/3685#18529508596) ([gh](https://github.com/pytorch/audio/actions/runs/6800069749/job/18529508596))

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[wasd96040501]

Hi @mthrok , I have implemented the changes, please take a look😊

[wasd96040501]

Hi, @mthrok It seems build conda failed. What can I do to fix this?

[mthrok]

Hi, @mthrok It seems build conda failed. What can I do to fix this?

@wasd96040501 This PR has nothing to do with build, and build jobs often fail for external reasons, so we don't need to worry about it.

FYI: I edited the test you added a bit.

[trangham283]

Hi, I think the current way to handle not has_triggered is wrong. It returns an empty tensor even if all the samples are non-zero. Here is a similar reproducible example to the one in https://github.com/pytorch/audio/issues/3668:

import torch
import torchaudio.functional as F
x = 10*torch.ones([16000])
y = F.vad(x, 16000)
print(f"input_size={x.size()}, ysize={y.size()}")

output: input_size=torch.Size([16000]), ysize=torch.Size([0])

I realize this is not the best example, as there is no speech in that array of all ones. Here is a sample that didn't trigger the flag even though there is speech in it, which led me to discover this.