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Fix macOS recording duration when final frames stop updating #685

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Fix macOS recording duration when final frames stop updating #685

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58 changes: 48 additions & 10 deletions electron/native/ScreenCaptureKitRecorder.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -370,16 +370,13 @@ final class ScreenCaptureRecorder: NSObject, SCStreamOutput, SCStreamDelegate {
stream = nil
isRecording = false

if let originalBuffer = lastSampleBuffer, let videoInput = videoInput {
let additionalTime = lastVideoPresentationTime + frameDuration(for: originalBuffer)
let timing = CMSampleTimingInfo(duration: originalBuffer.duration, presentationTimeStamp: additionalTime, decodeTimeStamp: originalBuffer.decodeTimeStamp)
if let additionalSampleBuffer = try? CMSampleBuffer(copying: originalBuffer, withNewTiming: [timing]) {
videoInput.append(additionalSampleBuffer)
}
}

let videoEndTime = lastVideoPresentationTime + (lastSampleBuffer.map { frameDuration(for: $0) } ?? .zero)
let endTime = resolvedCaptureEndTime(videoEndTime: videoEndTime)
let captureEndTime = currentAdjustedCaptureTime()
let paddedVideoEndTime = appendFinalVideoFrameIfNeeded(
videoEndTime: videoEndTime,
captureEndTime: captureEndTime
)
let endTime = resolvedCaptureEndTime(videoEndTime: paddedVideoEndTime)
assetWriter?.endSession(atSourceTime: endTime)
videoInput?.markAsFinished()
inlineAudioInput?.markAsFinished()
Expand Down Expand Up @@ -469,6 +466,48 @@ final class ScreenCaptureRecorder: NSObject, SCStreamOutput, SCStreamDelegate {
return CMTime(value: 1, timescale: CMTimeScale(targetCaptureFPS))
}

private func currentAdjustedCaptureTime() -> CMTime {
guard firstSampleTime != .zero else {
return .zero
}

let now = CMClockGetTime(CMClockGetHostTimeClock())
let pauseDurationInProgress: CMTime
if isPaused, let pauseStartedHostTime {
pauseDurationInProgress = max(.zero, now - pauseStartedHostTime)
} else {
pauseDurationInProgress = .zero
}

return max(.zero, now - firstSampleTime - accumulatedPausedDuration - pauseDurationInProgress)
}

private func appendFinalVideoFrameIfNeeded(videoEndTime: CMTime, captureEndTime: CMTime) -> CMTime {
guard let originalBuffer = lastSampleBuffer, let videoInput else {
return videoEndTime
}

let duration = frameDuration(for: originalBuffer)
let minimumAdditionalTime = videoEndTime
let targetPresentationTime = max(
minimumAdditionalTime,
captureEndTime - duration
)
let timing = CMSampleTimingInfo(
duration: duration,
presentationTimeStamp: targetPresentationTime,
decodeTimeStamp: originalBuffer.decodeTimeStamp
)
if let finalSampleBuffer = try? CMSampleBuffer(copying: originalBuffer, withNewTiming: [timing]),
videoInput.append(finalSampleBuffer) {
lastVideoPresentationTime = targetPresentationTime
lastVideoDuration = duration
return targetPresentationTime + duration
}

return videoEndTime
}
Comment on lines +485 to +509

@coderabbitai coderabbitai Bot Jun 16, 2026

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⚠️ Potential issue | 🟠 Major | ⚡ Quick win

Only append the padding frame when the video actually ends early.

As written, this appends whenever lastSampleBuffer exists. When captureEndTime <= videoEndTime, targetPresentationTime becomes videoEndTime, so the returned end time is extended by one extra frame even though no padding was needed.

Proposed fix 
 private func appendFinalVideoFrameIfNeeded(videoEndTime: CMTime, captureEndTime: CMTime) -> CMTime {
 	guard let originalBuffer = lastSampleBuffer, let videoInput else {
 		return videoEndTime
 	}
+
+	guard CMTimeCompare(captureEndTime, videoEndTime) > 0 else {
+		return videoEndTime
+	}
 
 	let duration = frameDuration(for: originalBuffer)
 	let minimumAdditionalTime = videoEndTime
 	let targetPresentationTime = max(
 		minimumAdditionalTime,
 		captureEndTime - duration
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
private func appendFinalVideoFrameIfNeeded(videoEndTime: CMTime, captureEndTime: CMTime) -> CMTime {
guard let originalBuffer = lastSampleBuffer, let videoInput else {
return videoEndTime
}
let duration = frameDuration(for: originalBuffer)
let minimumAdditionalTime = videoEndTime
let targetPresentationTime = max(
minimumAdditionalTime,
captureEndTime - duration
)
let timing = CMSampleTimingInfo(
duration: duration,
presentationTimeStamp: targetPresentationTime,
decodeTimeStamp: originalBuffer.decodeTimeStamp
)
if let finalSampleBuffer = try? CMSampleBuffer(copying: originalBuffer, withNewTiming: [timing]),
videoInput.append(finalSampleBuffer) {
lastVideoPresentationTime = targetPresentationTime
lastVideoDuration = duration
return targetPresentationTime + duration
}
return videoEndTime
}
private func appendFinalVideoFrameIfNeeded(videoEndTime: CMTime, captureEndTime: CMTime) -> CMTime {
guard let originalBuffer = lastSampleBuffer, let videoInput else {
return videoEndTime
}
guard CMTimeCompare(captureEndTime, videoEndTime) > 0 else {
return videoEndTime
}
let duration = frameDuration(for: originalBuffer)
let minimumAdditionalTime = videoEndTime
let targetPresentationTime = max(
minimumAdditionalTime,
captureEndTime - duration
)
let timing = CMSampleTimingInfo(
duration: duration,
presentationTimeStamp: targetPresentationTime,
decodeTimeStamp: originalBuffer.decodeTimeStamp
)
if let finalSampleBuffer = try? CMSampleBuffer(copying: originalBuffer, withNewTiming: [timing]),
videoInput.append(finalSampleBuffer) {
lastVideoPresentationTime = targetPresentationTime
lastVideoDuration = duration
return targetPresentationTime + duration
}
return videoEndTime
}
🤖 Prompt for 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.

In `@electron/native/ScreenCaptureKitRecorder.swift` around lines 485 - 509, The
appendFinalVideoFrameIfNeeded function appends a padding frame whenever
lastSampleBuffer exists, but should only append when the video actually ends
early relative to the capture. When captureEndTime is less than or equal to
videoEndTime, the targetPresentationTime becomes equal to videoEndTime due to
the max() calculation, resulting in an unnecessary extra frame. Add a condition
before creating and appending the final sample buffer to check that
captureEndTime is actually greater than videoEndTime, ensuring padding is only
added when needed to fill the gap between video and capture end times.


private func latestInlineAudioEndTime() -> CMTime {
guard lastInlineAudioPresentationTime.isValid else {
return .invalid
Expand Down Expand Up @@ -715,4 +754,3 @@ DispatchQueue.global(qos: .utility).async {
}

service.waitUntilFinished()