AVAssetExportSession -如何从视频持续时间修剪毫秒

Question

使用AVAssetExportSession时，如何从videoUrl修剪毫秒?我使用下面的代码，根据资产的数量和它们的时间框架，最终视频的持续时间为15.233333334秒或17.9333333334秒。一旦它们都加在一起，我想把mixComposition调整为15秒，17秒，等等。

AVMutableComposition:

let mixComposition = AVMutableComposition()

let compositionVideoTrack = mixComposition.addMutableTrack(withMediaType: .video, preferredTrackID: Int32(kCMPersistentTrackID_Invalid))
let soundtrackTrack = mixComposition.addMutableTrack(withMediaType: .audio, preferredTrackID: Int32(kCMPersistentTrackID_Invalid))
var insertTime = CMTime.zero
for videoAsset in videoAssets {
do {
let videoTrack = videoAsset.tracks(withMediaType: .video)
try compositionVideoTrack?.insertTimeRange(CMTimeRangeMake(start: CMTime.zero, duration: videoAsset.duration), videoAsset.tracks(withMediaType: .video)[0], at: insertTime)
let audioTrack = videoAsset.tracks(withMediaType: .audio)
try soundtrackTrack?.insertTimeRange(CMTimeRangeMake(start: CMTime.zero, duration: videoAsset.duration), videoAsset.tracks(withMediaType: .audio)[0], at: insertTime)
insertTime = CMTimeAdd(insertTime, videoAsset.duration)
} catch {
}
}

AVAssetExportSession:

guard let exporter = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPresetHighestQuality) else { return }
let start = CMTimeMakeWithSeconds(.zero, preferredTimescale: 600)
let videoDuration = CMTimeMakeWithSeconds(mixComposition.duration, preferredTimescale: 600)
let range = CMTimeRangeMake(start: start, duration: videoDuration)
exporter.timeRange = range
// ...

Answer 1

我发现了一个简单的方法。有一个名为trunc()的内置方法，它截断任何余数，只留下一个整数。

如果使用AVMutableComposition():

let mixComposition = AVMutableComposition()
// ...
let videoDuration = CMTimeGetSeconds(mixComposition.duration)
let dub = Double(videoDuration)
let durationTruncated = trunc(dub)
print(".......truncate: ", durationTruncated)
let duration = CMTimeMakeWithSeconds(durationTruncated, preferredTimescale: 600)
let start = CMTimeMakeWithSeconds(.zero, preferredTimescale: 600)
let range = CMTimeRangeMake(start: start, duration: duration)
exporter.timeRange = range

如果使用来自photoLibrary的url:

let asset = AVURLAsset(url: yourLibraryUrl) // if this isn't a libraryUrl you will need to run it through asset.loadValuesAsynchronously and use the "duration" asset key to get the duration first
let videoDuration = CMTimeGetSeconds(asset.duration)
let dub = Double(videoDuration)
let durationTruncated = trunc(dub)
print(".......truncate: ", durationTruncated)
let duration = CMTimeMakeWithSeconds(durationTruncated, preferredTimescale: 600)
let start = CMTimeMakeWithSeconds(.zero, preferredTimescale: 600)
let range = CMTimeRangeMake(start: start, duration: duration)
exporter.timeRange = range