Remove registration of video/audio callbacks based on TrackSource

[stephen-derosa]

bridge changes were only applied to truly purge the public API of this improper implementation.

[Copilot]

Pull request overview

This PR updates the SDK callback registration model to be keyed by (participant_identity, track_name) (removing TrackSource-based registration), and extends the video pipeline to optionally carry packet-trailer metadata (user timestamps / frame IDs) through capture, publish options, and receive callbacks.

Changes:

• Removed TrackSource-keyed audio/video callback registration and updated Room/dispatcher/bridge APIs and tests to use track names.
• Added video frame metadata support via VideoFrameMetadata / VideoCaptureOptions, protobuf conversion helpers, and a richer VideoFrameEvent callback path.
• Added unit + integration tests for metadata round-tripping and updated test build/linking (notably for Windows protobuf symbol handling).

Reviewed changes

Copilot reviewed 29 out of 29 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/video_utils.h	Adds proto conversions for optional video frame metadata.
src/video_utils.cpp	Implements metadata conversions and minor const-correctness tweaks.
src/video_stream.cpp	Populates VideoFrameEvent with optional received metadata.
src/video_source.cpp	Adds VideoCaptureOptions overload and forwards optional metadata to FFI.
src/video_frame.cpp	Simplifies pointer casts and minor formatting changes in owned-buffer copy path.
src/tests/unit/test_video_frame_metadata.cpp	New unit tests for metadata/proto conversions and publish options trailer features.
src/tests/unit/test_subscription_thread_dispatcher.cpp	Updates dispatcher tests to use track-name keyed callbacks.
src/tests/unit/test_room_callbacks.cpp	Updates room callback tests to use track-name keyed callbacks.
src/tests/integration/test_video_frame_metadata.cpp	New integration test validating metadata round-trip to receiver callback.
src/tests/CMakeLists.txt	Adjusts test linking/includes, including Windows protobuf symbol handling.
src/subscription_thread_dispatcher.cpp	Removes source-keyed paths; adds event callback registration and dispatch.
src/room.cpp	Routes subscribe/unsubscribe events using track-name keyed dispatcher API.
src/room_proto_converter.cpp	Adds proto conversion for PacketTrailerFeatures within TrackPublishOptions.
include/livekit/video_stream.h	Extends VideoFrameEvent with optional metadata and clarifies timestamp semantics.
include/livekit/video_source.h	Introduces VideoFrameMetadata + VideoCaptureOptions and new capture overload.
include/livekit/subscription_thread_dispatcher.h	Updates public dispatcher API to track-name keys; adds VideoFrameEventCallback.
include/livekit/room.h	Updates public Room callback APIs (track-name key) and adds video frame event callback setter.
include/livekit/room_event_types.h	Adds PacketTrailerFeatures and wires into TrackPublishOptions.
bridge/tests/test_livekit_bridge.cpp	Updates bridge callback tests to use track names.
bridge/src/livekit_bridge.cpp	Updates bridge callback registration/clearing to use track names.
bridge/README.md	Updates bridge documentation to describe track-name keyed callbacks.
bridge/include/livekit_bridge/livekit_bridge.h	Updates bridge public header docs and signatures to use track names.
AGENTS.md	Adds guidelines on fixed-width integer type usage.
.token_helpers/set_data_track_test_tokens.bash	Adds helper script to generate and export integration-test tokens.
.token_helpers/README.md	Adds brief documentation for token helper scripts.
.token_helpers/gen_and_set.bash	Adds helper script to generate and export a single token for local use.
.github/workflows/builds.yml	Disables clang-tidy thread comments in CI configuration.

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[alan-george-lk]

LGTM, just confirming (other than bridge) all of the header changes are in private scope (I think they are but hard to tell from PR diff)

[stephen-derosa]

LGTM, just confirming (other than bridge) all of the header changes are in private scope (I think they are but hard to tell from PR diff)

these changes touch public api code -- it breaks usage. We will major bump next release

[stephen-derosa]

I added this chunk here to keep track of deprecated and breaking changes. If we decide to not introduce breaking changes right now, we can just commit the README changes and officially remove with the bridge on 06/01.