potential fix: av foundation take the duration from the matched range… - #1314
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…'s own bounds instead of deriving it from the rounded fps.
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| } else { | ||
| // The rate lies strictly inside the range, so its reciprocal lies | ||
| // strictly inside the range's duration bounds. | ||
| // SAFETY: `requested` is finite and greater than zero here. | ||
| unsafe { CMTime::with_seconds(1.0 / requested, 600) } |
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🟡 Requested frame rates that don't divide evenly can still crash the app on some cameras
The frame time is rounded to a fixed 600-tick clock (CMTime::with_seconds(1.0 / requested, 600) at livekit-capture/src/sources/device/avfoundation.rs:957) without being clamped to what the camera advertises, so for rates such as 45 the value can land just outside the accepted window and abort the app.
Impact: On certain cameras, asking for a frame rate the fixed clock cannot represent exactly makes the application terminate instead of starting capture.
Rounding to a 600 timescale can exceed the range's minFrameDuration
device_format_frame_duration snaps to maxFrameDuration/minFrameDuration only at the endpoints; for a rate strictly inside the range it derives the duration from 1.0 / requested with timescale 600. Only rates that divide 600 (1,2,3,4,5,6,8,10,12,15,20,24,25,30,40,50,60,75,…) are exactly representable. For 45 fps, 600/45 = 13.33 rounds to 13 ticks → 46.15 fps, i.e. a duration shorter than the range's minFrameDuration whenever maxFrameRate lies in (45, 46.15) — exactly the near-integral advertised maxima this PR was written to handle (e.g. max = 45.00003). The resulting value is then handed to device.setActiveVideoMinFrameDuration/setActiveVideoMaxFrameDuration (livekit-capture/src/sources/device/avfoundation.rs:1033-1036) or input.setActiveLockedVideoFrameDuration (livekit-capture/src/sources/device/avfoundation.rs:443), which raises the uncatchable Objective-C exception the comment describes.
Prompt for agents
In device_format_frame_duration (livekit-capture/src/sources/device/avfoundation.rs), the interior-of-range case builds the duration with CMTime::with_seconds(1.0 / requested, 600). A timescale of 600 cannot exactly represent every integer frame rate (e.g. 45 fps needs 13.33 ticks), and CMTimeMakeWithSeconds rounds, so the resulting duration can be shorter than the range's minFrameDuration when maxFrameRate is only slightly above the requested rate. Since an out-of-range duration triggers an uncatchable Objective-C exception at the setActiveVideoMin/MaxFrameDuration and setActiveLockedVideoFrameDuration call sites, the computed duration should be exact and/or clamped. Options: build the CMTime exactly as value=1, timescale=framerate, and/or clamp the resulting CMTime into [minFrameDuration, maxFrameDuration] of the matched range before returning.
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ladvoc
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ladvoc
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Makes sense to me! What version of macOS did you test on?
26.5.2 (25F84)! |
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