Fix Safari iOS video time scale#2457
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soulgalore merged 1 commit intomainfrom May 5, 2026
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When recording an iPhone over USB the captured video used to play back at half wall-clock speed, which made every visualmetrics-derived metric (FirstVisualChange, VisualComplete85, LastVisualChange and the filmstrip frame timestamps) drift away from the browser metrics that sitespeed.io renders alongside them. On the visual progress card you could see FCP and LCP markers landing in completely different places than the matching filmstrip thumbnails — the symptom that prompted this fix. The reason is that AVFoundation delivers iOS screen-capture frames at the device's display refresh rate, and ios-capture was telling its ffmpeg encoder the input was 30 fps regardless. Encoding 60 frames per real second as a 30 fps stream stretches the timeline by 2x. This change defaults ios-capture and the Safari driver to 60 fps so the encoded video matches the device's actual delivery rate. ProMotion devices may need a follow-up with PTS-correct frames via AVAssetWriter, but for 60 Hz iPhones the timelines now line up to within one frame. Co-authored-by: Claude Opus 4.7 (1M context) noreply@anthropic.com Change-Id: I265ca6fe8e3cccfaa88234be3cfb4a5a2ec70b75
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When recording an iPhone over USB the captured video used to play back at half wall-clock speed, which made every visualmetrics-derived metric (FirstVisualChange, VisualComplete85, LastVisualChange and the filmstrip frame timestamps) drift away from the browser metrics that sitespeed.io renders alongside them. On the visual progress card you could see FCP and LCP markers landing in completely different places than the matching filmstrip thumbnails — the symptom that prompted this fix.
The reason is that AVFoundation delivers iOS screen-capture frames at the device's display refresh rate, and ios-capture was telling its ffmpeg encoder the input was 30 fps regardless. Encoding 60 frames per real second as a 30 fps stream stretches the timeline by 2x.
This change defaults ios-capture and the Safari driver to 60 fps so the encoded video matches the device's actual delivery rate. ProMotion devices may need a follow-up with PTS-correct frames via AVAssetWriter, but for 60 Hz iPhones the timelines now line up to within one frame.
Co-authored-by: Claude Opus 4.7 (1M context) noreply@anthropic.com
Change-Id: I265ca6fe8e3cccfaa88234be3cfb4a5a2ec70b75