[Partner Nodes] feat(bria): add Transparent option to Remove Video Background

[guill]

PR Created by the Glary-Bot Agent

---

Why

Bria asked for the "Transparent" output to live inside the Bria Remove Video Background node as just another background_color dropdown value, rather than a separate Bria Remove Video Background (Transparent) node. This PR is the smallest change that adds it.

Draft on purpose — there is a UX caveat we should decide how to handle before merging. See "Open question" below.

What changed

comfy_api_nodes/nodes_bria.py:

• BriaRemoveVideoBackground now exposes Transparent in the background_color dropdown.
• When background_color == "Transparent", the node sends output_container_and_codec="webm_vp9" to Bria (Bria returns 422 if you pair Transparent with mp4_h264). Everything else still sends mp4_h264.
• Dropdown default explicitly pinned to "Black" to preserve the prior implicit default; Transparent is at the end of the list.
• Descriptions/tooltips on both BriaRemoveVideoBackground and BriaTransparentVideoBackground reworked to make the division of labor explicit and call out the Save Video alpha-drop issue.
• BriaTransparentVideoBackground (the IMAGE + MASK node) is unchanged and not deprecated — see "Why both still exist".

tests-unit/comfy_api_test/video_types_test.py:

• New test_video_from_file_save_to_bytesio_stream_copies_vp9_alpha: builds a synthetic WebM/VP9 video with a deliberately varying alpha plane, runs it through VideoFromFile.save_to(BytesIO, format=AUTO, codec=AUTO), and confirms alpha decodes back identically via libvpx-vp9. Test name and docstring scope it precisely to the in-memory BytesIO path; the .mp4 file-path case (SaveVideo's default) is intentionally not covered because it drops alpha (see PR notes).

Why both nodes still exist (and the new node isn't a full replacement)

I tested the end-to-end flow on a synthetic VP9 + alpha file, and there are two ComfyUI-core gaps that mean the consolidated node is not yet equivalent to the dedicated transparent node:

1. Get Video Components cannot expose the alpha plane for VP9. VideoFromFile.get_components_internal decodes with PyAV's default vp9 decoder, which drops the side alpha layer before the alpha-detection code at comfy_api/latest/_input_impl/video_types.py:291-321 runs. The existing BriaTransparentVideoBackground works around this by manually constructing CodecContext.create("libvpx-vp9", "r") (see _video_to_images_and_mask). Until core grows VP9-alpha decoding, anyone who wants images + mask sockets has to use the dedicated node.
2. Save Video with default auto/auto writes a .mp4 file, and muxing a VP9 stream into MP4 drops the alpha plane. Confirmed locally: source [50, 100, 151, 201, 251] per-frame alpha decodes back as [255, 255, 255, 255, 255] after a round-trip through a .mp4 path. VideoContainer doesn't have a WebM option today, so users can't simply pick a different format either.

So BriaTransparentVideoBackground is the only path that actually delivers an alpha-channel result to disk today. The PR makes that explicit in both nodes' descriptions.

Open question for review

The consolidated "Transparent" option technically works — Bria returns the right file, the file passes through the graph carrying alpha bytes — but the only thing the user can do with it today is feed it back into the graph in memory or write it to disk losing alpha. Options:

• Ship as-is (this PR): honest descriptions, no surprises. The consolidated node is mostly useful as a forward-looking entry point once core video alpha support lands.
• Extend scope: add WebM to VideoContainer, teach SaveVideo to pick the right extension based on source codec/container, optionally surface VideoComponents.alpha from GetVideoComponents. Bigger blast radius (touches core video code that every node uses).
• Defer: don't add Transparent to the consolidated node yet; just clean up the descriptions of the two existing nodes to clarify the split.

I lean toward shipping this PR as-is and filing follow-ups for the two core issues — but it's your call. Not marking ready-for-review until that's decided.

Verification

• ruff check comfy_api_nodes/nodes_bria.py tests-unit/comfy_api_test/video_types_test.py — clean.
• python -m pytest tests-unit/comfy_api_test/video_types_test.py — 16 passed, including the new VP9-alpha round-trip test.
• Manual: synthetic VP9 + alpha encode → VideoFromFile → save_to confirmed (a) byte-exact alpha preservation when target is BytesIO/.webm, (b) alpha-dropping when target is .mp4 (which is what SaveVideo does by default — the caveat we're being honest about).
• No live Bria API testing in this environment (no API key, no GPU).

Follow-ups (not in this PR)

• Patch VideoFromFile.get_components_internal to fall back to libvpx-vp9 when the stream codec is vp9 so alpha decoding works for every VP9 input, then surface an optional mask output on GetVideoComponents.
• Add webm_vp9 to VideoContainer/VideoCodec and teach SaveVideo to choose the extension based on the source's container/codec when in auto mode.
• Once both land, BriaTransparentVideoBackground can actually be deprecated.

API Node PR Checklist

Scope

• Is API Node Change

Pricing & Billing

• Need pricing update
• No pricing update

If Need pricing update:

• Metronome rate cards updated
• Auto‑billing tests updated and passing

QA

• QA done
• QA not required

Comms

• Informed Kosinkadink