[v1.2] Document ZCC uses channel_id (not metadata.userName) for speaker identification

[MaxMansfield]

Context

SDK examples and docs (examples/node.md, examples/python.md) show identifying speakers in on_transcript_data / on_audio_data callbacks via metadata.userName (Node) / metadata.user_name (Python). This field is not present (or not meaningful) for ZCC events. ZCC RTMS streams identify participants via a channel_id on the packet/metadata — see [ADR-2026-05-08 — RTMS audio packet channel ID is ZCC-only].

Customers building ZCC integrations copy-paste the standard example, get None / undefined for the speaker, and assume the SDK is broken.

What to ship

1. Update examples/python.md — add a ZCC-specific subsection under the audio/transcript callback examples showing the right way to identify a speaker:

@client.on_transcript_data
def _(data, size, ts, metadata):
    speaker = metadata.channel_id        # ZCC routes by channel
    text    = data.decode("utf-8", errors="replace")
    print(f"channel {speaker}: {text}")

2. Update examples/node.md — same pattern in JS:

client.onTranscriptData((data, size, ts, metadata) => {
    const speaker = metadata.channelId;
    console.log(`channel ${speaker}: ${data.toString()}`);
});

3. Mark userName / user_name as Optional in type stubs (__init__.pyi Python, rtms.d.ts Node) — document that it's populated only for Zoom Meetings / Webinars streams, not ZCC.

4. Add channel_id / channelId to type stubs as Optional — populated only for ZCC streams.

5. Update examples/zcc.md with a cross-link to the new sections in the language guides.

Acceptance criteria

• ZCC speaker-identification section added to examples/python.md
• ZCC speaker-identification section added to examples/node.md
• userName / user_name marked Optional in both type stub sets
• channel_id / channelId documented in both type stub sets
• examples/zcc.md cross-links to the new language sections
• Confirmed with a real ZCC RTMS stream that metadata.channel_id is populated and metadata.user_name is empty

Cross-language parity

• examples/python.md and examples/node.md updated in the same PR
• Same structure, same code examples
• Type stub updates ship together
• PR description includes "Cross-language parity check" section

Source

Tracked in vault: Projects/RTMS SDK v1.2.md → DEVS-X15. Builds on the 2026-05-08 ADR.

Tracker

Part of the v1.2 milestone. Project: https://github.com/orgs/zoom/projects/11.