feat: iOS video renderer improvements

[Brazol]

Summary by CodeRabbit

• Performance Improvements
  • Improved video rendering efficiency through zero-copy frame delivery where supported.
  • Reduced visual processing overhead by reusing video buffers and optimizing rotation, cropping, and scaling.
• Bug Fixes
  • Corrected video-track switching to properly detach the previous track before attaching a new one.
• Rendering
  • Updated iOS platform-view rendering for smoother, more consistent video playback.

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: d7a3a605-e1c6-4743-906d-4c9c2d98607b

📥 Commits

Reviewing files that changed from the base of the PR and between 1c8a212 and 0ba15ef.

📒 Files selected for processing (2)

• ios/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterRTCVideoRenderer.m
• macos/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterRTCVideoRenderer.m

📝 Walkthrough

Walkthrough

The changes replace iOS sample-buffer rendering with WebRTC shared Metal rendering, correct previous-track detachment, and update iOS/macOS texture renderers to reuse buffers, optimize NV12 delivery, handle rotation efficiently, and retain the current frame buffer.

Changes

Video rendering pipeline

Layer / File(s)	Summary
Platform view and track integration ios/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterRTCVideoPlatformView.m, ios/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterRTCVideoPlatformViewController.m	The iOS platform view forwards layout, size, and frames to RTCVideoRenderingView using the shared Metal backend, while track replacement detaches an existing previous track.
Reusable renderer buffers and rotation ios/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterRTCVideoRenderer.m, macos/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterRTCVideoRenderer.m	Renderers retain the current output buffer, reuse NV12, crop, and rotated I420 buffers, and release the added resources during disposal.
NV12 and texture frame delivery ios/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterRTCVideoRenderer.m, macos/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterRTCVideoRenderer.m	Frame handling attempts zero-copy or reused NV12 output before falling back to I420 conversion, then publishes the selected buffer through the texture registry.

Estimated code review effort: 4 (Complex) | ~45 minutes

Sequence Diagram(s)

sequenceDiagram
  participant RTCVideoFrame
  participant FlutterRTCVideoRenderer
  participant FlutterTextureRegistry
  RTCVideoFrame->>FlutterRTCVideoRenderer: provide video frame
  FlutterRTCVideoRenderer->>FlutterRTCVideoRenderer: select zero-copy, NV12, or I420 output
  FlutterRTCVideoRenderer->>FlutterTextureRegistry: mark texture frame available
  FlutterTextureRegistry->>FlutterRTCVideoRenderer: request current pixel buffer
  FlutterRTCVideoRenderer-->>FlutterTextureRegistry: return retained current buffer

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the renderer-focused improvements, though it understates that macOS changes are included too.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chore/ios-render-improvements

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[coderabbitai]

Actionable comments posted: 3

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In
`@ios/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterRTCVideoRenderer.m`:
- Around line 70-84: Update ensureNV12BufferWithWidth:height: to accept the
source pixel format and use it when creating _nv12BufferRef, rather than always
selecting kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange. Pass renderFrame:’s
fmt through this method so both video-range and full-range NV12 frames retain
their correct color range.

In
`@macos/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterRTCVideoRenderer.m`:
- Around line 70-84: Update ensureNV12BufferWithWidth:height: to accept the
source fmt, create _nv12BufferRef with that format, and include fmt in the
reuse-validity check so a format change recreates the buffer. Propagate fmt from
the crop path and validate the CVPixelBufferCreate result before retaining or
using the buffer.
- Around line 245-293: Double-buffer the cropped NV12 output used by the
renderer: replace the single _nv12BufferRef handoff in cropAndScaleTo: with two
reusable NV12 pixel buffers, selecting the buffer not currently published as
_currentBuffer before each crop. Update ensureNV12BufferWithWidth:height: and
the cleanup/state handling so both buffers are allocated, reused, and released
safely, while preserving the existing zero-copy path for unpadded IOSurface
frames.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: f6e08697-bff9-4151-a880-c4d2358bde28

📥 Commits

Reviewing files that changed from the base of the PR and between d7098ba and 1c8a212.

📒 Files selected for processing (4)

• ios/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterRTCVideoPlatformView.m
• ios/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterRTCVideoPlatformViewController.m
• ios/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterRTCVideoRenderer.m
• macos/stream_webrtc_flutter/Sources/stream_webrtc_flutter/FlutterRTCVideoRenderer.m