我必须在视频中应用不透明度。我必须在一秒钟的视频结束之前应用它。我正在使用“ firstInstruction”获得视频的总时长。但是,当我调用“ firstInstruction.setOpacityRamp”方法时,我无法减去第二个方法。
let mainInstruction = AVMutableVideoCompositionInstruction()
mainInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeAdd(firstAsset.duration, secondAsset.duration))
let firstInstruction = VideoHelper.videoCompositionInstruction(firstTrack, asset: firstAsset)
firstInstruction.setOpacityRamp(fromStartOpacity: 1, toEndOpacity: 0.1, timeRange: mainInstruction.timeRange)
答案 0 :(得分:2)
我将使用三条指令进行淡入淡出:
所以,首先,让我们获得曲目:
import AVFoundation
import CoreVideo
func crossFade(asset0: AVAsset, asset1: AVAsset, crossFadeDuration: CMTime, to outputUrl: URL) throws {
guard
let asset0Track = asset0.tracks(withMediaType: .video).first,
let asset1Track = asset1.tracks(withMediaType: .video).first,
case let composition = AVMutableComposition(),
case let compositionTrack0Id = composition.unusedTrackID(),
let compositionTrack0 = composition.addMutableTrack(
withMediaType: .video, preferredTrackID: compositionTrack0Id),
case let compositionTrack1Id = composition.unusedTrackID(),
let compositionTrack1 = composition.addMutableTrack(
withMediaType: .video, preferredTrackID: compositionTrack1Id)
else { return }
现在让我们计算所需的所有时间。首先,构图中的asset0Track
的整个范围,包括通过和淡入淡出周期:
// When does asset0Track start, in the composition?
let asset0TrackStartTime = CMTime.zero
// When does asset0Track end, in the composition?
let asset0TrackEndTime = asset0TrackStartTime + asset0Track.timeRange.duration
接下来,淡入淡出的时间范围:
// When does the cross-fade end, in the composition?
// It should end exactly at the end of asset0's video track.
let crossFadeEndTime = asset0TrackEndTime
// When does the cross-fade start, in the composition?
let crossFadeStartTime = crossFadeEndTime - crossFadeDuration
// What is the entire time range of the cross-fade, in the composition?
let crossFadeTimeRange = CMTimeRangeMake(
start: crossFadeStartTime,
duration: crossFadeDuration)
接下来,构图中的asset1Track
的整个范围都包括淡入淡出和通过时间:
// When does asset1Track start, in the composition?
// It should start exactly at the start of the cross-fade.
let asset1TrackStartTime = crossFadeStartTime
// When does asset1Track end, in the composition?
let asset1TrackEndTime = asset1TrackStartTime + asset1Track.timeRange.duration
最后,两个通过时间范围:
// What is the time range during which only asset0 is visible, in the composition?
let compositionTrack0PassThroughTimeRange = CMTimeRangeMake(
start: asset0TrackStartTime,
duration: crossFadeStartTime - asset0TrackStartTime)
// What is the time range during which only asset1 is visible, in the composition?
let compositionTrack1PassThroughTimeRange = CMTimeRangeMake(
start: crossFadeEndTime,
duration: asset1TrackEndTime - crossFadeEndTime)
现在,我们可以将输入轨道插入到合成的轨道中:
// Put asset0Track into compositionTrack0.
try compositionTrack0.insertTimeRange(
asset0Track.timeRange,of: asset0Track, at: asset0TrackStartTime)
// Put asset1Track into compositionTrack1.
try compositionTrack1.insertTimeRange(
asset1Track.timeRange, of: asset1Track, at: asset1TrackStartTime)
这就是AVMutableComposition
要做的全部工作。但是我们还需要制作一个AVMutableVideoComposition
:
let videoComposition = AVMutableVideoComposition()
videoComposition.frameDuration =
min(asset0Track.minFrameDuration, asset1Track.minFrameDuration)
videoComposition.renderSize = CGSize(
width: max(asset0Track.naturalSize.width, asset1Track.naturalSize.width),
height: max(asset0Track.naturalSize.height, asset1Track.naturalSize.height))
我们需要设置视频合成的说明。第一条指令是在适当的时间范围内仅通过compositionTrack0
:
// I'm using a helper function defined below.
let compositionTrack0PassThroughInstruction = AVMutableVideoCompositionInstruction.passThrough(
trackId: compositionTrack0Id, timeRange: compositionTrack0PassThroughTimeRange)
第二条指令用于淡入淡出,因此更为复杂。它需要两个子指令,即淡入淡出中的每一层。每层指令以及整个淡入淡出指令都使用相同的时间范围:
let crossFadeLayer0Instruction = AVMutableVideoCompositionLayerInstruction()
crossFadeLayer0Instruction.trackID = compositionTrack0Id
crossFadeLayer0Instruction.setOpacityRamp(fromStartOpacity: 1, toEndOpacity: 0, timeRange: crossFadeTimeRange)
let crossFadeLayer1Instruction = AVMutableVideoCompositionLayerInstruction()
crossFadeLayer1Instruction.trackID = compositionTrack1Id
crossFadeLayer1Instruction.setOpacityRamp(fromStartOpacity: 0, toEndOpacity: 1, timeRange: crossFadeTimeRange)
let crossFadeInstruction = AVMutableVideoCompositionInstruction()
crossFadeInstruction.timeRange = crossFadeTimeRange
crossFadeInstruction.layerInstructions = [crossFadeLayer0Instruction, crossFadeLayer1Instruction]
第三条指令是在适当的时间范围内仅通过compositionTrack1
:
let compositionTrack1PassThroughInstruction = AVMutableVideoCompositionInstruction.passThrough(
trackId: compositionTrack1Id, timeRange: compositionTrack1PassThroughTimeRange)
现在我们已经掌握了全部三个指令,可以将它们用于视频合成:
videoComposition.instructions = [compositionTrack0PassThroughInstruction, crossFadeInstruction, compositionTrack1PassThroughInstruction]
现在我们可以一起使用composition
和videoComposition
,例如导出一个新的电影文件:
let export = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetMediumQuality)!
export.outputURL = outputUrl
export.videoComposition = videoComposition
export.exportAsynchronously {
exit(0)
}
}
这是我用来创建传递说明的助手:
extension AVMutableVideoCompositionInstruction {
static func passThrough(trackId: CMPersistentTrackID, timeRange: CMTimeRange) -> AVMutableVideoCompositionInstruction {
let layerInstruction = AVMutableVideoCompositionLayerInstruction()
layerInstruction.trackID = trackId
let instruction = AVMutableVideoCompositionInstruction()
instruction.timeRange = timeRange
instruction.layerInstructions = [layerInstruction]
return instruction
}
}
这是我的测试代码。我使用了macOS命令行应用进行测试:
let asset0 = AVURLAsset(url: URL(fileURLWithPath: "/tmp/asset0.mp4"))
let asset1 = AVURLAsset(url: URL(fileURLWithPath: "/tmp/asset1.mp4"))
let outputUrl = URL(fileURLWithPath: "/tmp/output.mp4")
try! crossFade(asset0: asset0, asset1: asset1, crossFadeDuration: CMTimeMake(value: 1, timescale: 1), to: outputUrl)
dispatchMain()
结果:
请注意,由于Stack Overflow对图片文件大小的限制,我必须使动画小而色彩淡。
由Jeffrey Beach提供输入视频。