Swift开发：CMTimeRange设置时出现警告问题求助

Hey, let's work through that warning you're seeing when setting up CMTimeRange for your export session. Even though your printed startTime and endTime look normal, there are a few common pitfalls that might be triggering the warning. Here's what to check:

1. Make sure start time doesn't come after end time #

While the raw values might look okay, differences in timescale (the units used to measure time) can make a startTime appear smaller numerically but actually be later than endTime when evaluated properly. Always use CMTimeCompare to validate this:

if CMTimeCompare(startTime, endTime) > 0 {
    print("Warning: Start time is later than end time!")
    // Handle this case (swap times, show error, etc.)
    return
}

2. Ensure the time range fits within the asset's total duration #

AVAssetExportSession will warn if your timeRange extends beyond the bounds of the source asset. Add a check against the asset's duration:

let assetTotalDuration = asset.duration
if CMTimeCompare(startTime, kCMTimeZero) < 0 || CMTimeCompare(endTime, assetTotalDuration) > 0 {
    print("Warning: Time range falls outside the asset's duration!")
    return
}

3. Use CMTimeRangeMakeWithStartAndDuration for safer initialization #

Instead of creating the range directly with start and end, building it from start time and duration can avoid precision issues that sometimes trigger warnings:

let clipDuration = CMTimeSubtract(endTime, startTime)
let safeTimeRange = CMTimeRangeMake(start: startTime, duration: clipDuration)
exportSession.timeRange = safeTimeRange

4. Align the timescale of your trimmer times with the asset #

If the startTime/endTime from your trimmerView use a different timescale than the source asset, this can cause unexpected parsing issues. Convert them to match the asset's timescale:

let targetTimescale = asset.duration.timescale
let convertedStartTime = CMTimeConvertScale(startTime, targetTimescale, .roundHalfAwayFromZero)
let convertedEndTime = CMTimeConvertScale(endTime, targetTimescale, .roundHalfAwayFromZero)
let alignedTimeRange = CMTimeRange(start: convertedStartTime, end: convertedEndTime)

If you can share the exact text of the warning you're seeing, that would help narrow things down even more!

内容的提问来源于stack exchange，提问作者jeongbalmountain