Cap heats up a lot gets excessively hot when recording video

[AasheeshLikePanner]

Description

Cap heats up a lot / gets excessively hot when recording video with both camera (webcam/facecam) and microphone turned on. The laptop becomes noticeably warm within just a few minutes, fans spin up louder, and it feels uncomfortably hot to touch. This happens even during short recordings (3–10 minutes).

Expected: Smooth recording without abnormal heating / high CPU/GPU usage when using camera + mic together. It seems worse than when recording screen only (no camera/mic).

Reproduction

1. Open Cap desktop app
2. Start a new screen recording
3. Turn ON both Camera (webcam overlay) and Microphone
4. Click record (with or without capturing screen — happens either way)
5. Record for 3–10 minutes → device gets significantly hot

Additional Context

• Operating system, version: macOS tahoe 26.3.1
• Device (optional): macbook air m4

[linear]

CAP-662

[tembo]

This issue is closely related to #586 (Laggy system while recording), which reports similar high CPU usage and system lag during recording on a MacBook Pro M1 Max. In that issue, a maintainer noted that the encoding uses VTEncoder via AVFoundation which is supposed to be hardware-accelerated, but may require different configuration for high-resolution encoding.

Relevant code areas for investigation:

• Camera feed processing: crates/recording/src/feeds/camera.rs - handles camera frame capture and distribution
• macOS output pipeline: crates/recording/src/output_pipeline/macos.rs - manages encoding with channel pressure tracking
• VideoToolbox integration: crates/frame-converter/src/videotoolbox.rs - pixel format conversion using VTPixelTransferSession

Diagnostic tools available:

The codebase includes a camera benchmark that could help isolate whether the issue is in capture, conversion, or encoding:

cd apps/desktop
cargo run --example camera-benchmark --release

This measures frame rate, inter-frame timing, and full encoding pipeline performance.

Potential contributing factors:

1. The camera format selection in select_camera_format filters for formats under 2000x2000 and 30fps+, but simultaneous screen + camera encoding at high resolutions may still stress the encoder
2. Frame conversion between camera pixel formats and encoder input (UYVY/YUYV to NV12) happens on CPU via the converter pool
3. Multiple encoding streams (screen + camera) running in parallel compounds resource usage

Attaching diagnostic logs via the app's "Upload Logs" feature would help identify whether frame drops or encoder backpressure are occurring.

[tembo]

This issue is related to several existing reports about CPU usage during recording:

• #586 - Reports 100% CPU usage with GPU not being used during recording with webcam on MacBook Pro M1 Max. A contributor noted that Cap uses VTEncoder via AVFoundation which should be hardware accelerated, but may need different configuration for certain resolutions.
• #988 - Similar report of all available CPU being used on Apple M4 Max with laggy/patchy video output.
• #109 - Tracks CPU/memory optimization during recording, with reports of the issue reproducing specifically when recording with webcam + mic enabled.

Relevant code areas:

• Camera capture pipeline: crates/recording/src/sources/camera.rs - handles frame scaling via FFmpeg's software scaler when camera dimensions change
• Camera feed processing: crates/recording/src/feeds/camera.rs
• macOS camera backend: crates/camera-avfoundation/src/lib.rs
• Output encoding: crates/recording/src/output_pipeline/macos.rs

Diagnostic tools available:
The codebase includes a camera benchmark example at crates/recording/examples/camera-benchmark.rs that can help measure frame rate and encoding performance. Running this could help identify whether the bottleneck is in capture, color conversion, or encoding:

cargo run --release --example camera-benchmark

The camera source uses a software scaler (ffmpeg::software::scaling::Context) when frame dimensions don't match the expected output, which runs on CPU. If the webcam is delivering frames at a different resolution than expected, this could contribute to CPU load.

For debugging, logs from ~/Library/Logs/so.cap.desktop/ would help determine if frames are being dropped due to the encoder not keeping up (look for "encoder can't keep up" warnings).