Add audio property to VideoDecoder

[Samoed]

Previously, accessing audio from a video file required creating a separate AudioDecoder alongside VideoDecoder #1158. This split made it difficult to integrate with external libraries such as huggingface datasets utilities that expect audio to be accessible directly from the video decoder - the absence of an audio attribute on VideoDecoder either required workarounds or left audio support missing entirely in those integrations.

This PR adds a lazy audio property to VideoDecoder that returns an AudioDecoder for audio stream in the same source, or None if the source contains no audio stream

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/meta-pytorch/torchcodec/1442

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❗ 1 Active SEVs

There are 1 currently active SEVs. If your PR is affected, please view them below:

• Run pull request jobs on OSDC runners in shadow mode

This comment was automatically generated by Dr. CI and updates every 15 minutes.

[NicolasHug]

Hi @Samoed , can you share more about this:

This split made it difficult to integrate with external libraries such as huggingface/datasets#8007 utilities that expect audio to be accessible directly from the video decoder - the absence of an audio attribute on VideoDecoder either required workarounds or left audio support missing entirely in those integrations

Specifically I'd like to understand why having two seprate VideoDecoder and AudioDecoder objects lead to friction, and how does the proposed design solve it

[Samoed]

The Datasets library outputs video inputs as VideoDecoder, and to be able to easily extract audio information it typically splits inputs into video and audio columns before uploading. Extracting audio input from such videos requires some hacks. Also, I think it would be good to be able to work with one object during data processing to handle both audio and video