Update the logic to fetch pixel format from filter graph

[mthrok]

When using GPU decoder in some environments, attempting to read the output formats from filter graph caused an issue in which the software pixel format cannot be determined.

We do not know the exact cause but when it happens, the input link of buffer sink does not have HW frames context.

Since currently no filter can convert the pixel format of CUDA frame, we resort to the HW frames context of the output link of buffer source.

Environments this was observed.

Env1

• OS: Fedora 36 (x86_64)
• GCC 12.2.1
• Python 3.10.12
• GPU: GeForce RTX 3070 Ti Laptop GPU
• FFmpeg: 5.1.3
• nv-codec-header: n11.1.5.2
• CUDA: 12.1

Env2

• Ubuntu 20.04.4 LTS (x86_64)
• GCC 9.4.0
• Python 3.11.3
• GPU: Quadro GV100
• FFmpeg: 5.1.3
• nv-codec-header: n11.1.5.2
• CUDA: 11.4

[pytorch-bot]

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❌ 2 New Failures

As of commit 72ef2d1:

NEW FAILURES - The following jobs have failed:

• build (3.8) (gh)
• tests / macos-job (gh)

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@mthrok has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@mthrok merged this pull request in cf53a48.

[github-actions]

Hey @mthrok.
You merged this PR, but labels were not properly added. Please add a primary and secondary label (See https://github.com/pytorch/audio/blob/main/.github/process_commit.py).

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