使用帧方法的带音频慢动作视频-iOS [英] Slow Motion Video with Audio using frames approach - iOS

问题描述

我必须使用基于帧的方法将视频转换为带音频的慢动作.以下链接是很多帮助，这是反向-AVAsset-高效

I have to convert video to slow motion with audio using frame base approach. Following links were lot of help which are Reverse-AVAsset-Efficient

在解决方案中，我可以更改缓冲区的时间戳并获得慢动作视频.

In solution I can change the timestamp of the buffer and achieve slow motion video.

for sample in videoSamples {
   var presentationTime = CMSampleBufferGetPresentationTimeStamp(sample)

   //Changing Timestamp to achieve slow-motion 
   presentationTime.timescale = presentationTime.timescale * 2

   let imageBufferRef = CMSampleBufferGetImageBuffer(sample)
   while !videoWriterInput.isReadyForMoreMediaData {
     Thread.sleep(forTimeInterval: 0.1)
   }
   pixelBufferAdaptor.append(imageBufferRef!, withPresentationTime: presentationTime)
}

对于音频慢动作，我尝试更改音频样本的时间戳，但没有任何效果.

for audio slow motion I tried to change the timestamp of audio sample but it has no effect.

是否有用于音频慢动作的解决方案.

Is there any solution for Audio slow-motion.

如果您有Objective-C解决方案，请随时发布.谢谢.

If you have Objective-C solution, feel free to post it. Thanks.

推荐答案

您可以使用 AVMutableComposition 轻松慢动作.正如@ hotpaw2所提到的，有多种方法可以降低音频速度-例如，您可以降低音调或使其保持恒定.这种解决方案似乎可以保持不变，我看不出有任何方法可以改变它.也许这就是您想要的.也许不会.

You can do an easy slow motion using AVMutableComposition. As @hotpaw2 mentioned, there is more than one way to slow down your audio - for example you could lower the pitch or keep it constant. This solution seems to keep it constant and I don't see any way to change that. Maybe that's what you want. Maybe not.

您可以使用 AVAssetExportSession 将慢速视频写到文件中，并且 AVMutableComposition 是 AVAsset 的子类(也许令人惊讶)，即使您没有导出慢动作版本，也可以使用 AVPlayer 预览结果.的视频.

You can use AVAssetExportSession to write the slow video out to a file, and since AVMutableComposition is (perhaps surprisingly) a subclass of AVAsset, you can preview the results using AVPlayer even if you haven't exported the slow motion version of the video.

let asset = AVURLAsset(url: Bundle.main.url(forResource: "video", withExtension: "mp4")! , options : nil)

let srcVideoTrack = asset.tracks(withMediaType: .video).first!
let srcAudioTrack = asset.tracks(withMediaType: .audio).first!

let sloMoComposition = AVMutableComposition()
let sloMoVideoTrack = sloMoComposition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)!
let sloMoAudioTrack = sloMoComposition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid)!

let assetTimeRange = CMTimeRange(start: .zero, duration: asset.duration)

try! sloMoVideoTrack.insertTimeRange(assetTimeRange, of: srcVideoTrack, at: .zero)
try! sloMoAudioTrack.insertTimeRange(assetTimeRange, of: srcAudioTrack, at: .zero)

let newDuration = CMTimeMultiplyByFloat64(assetTimeRange.duration, multiplier: 2)
sloMoVideoTrack.scaleTimeRange(assetTimeRange, toDuration: newDuration)
sloMoAudioTrack.scaleTimeRange(assetTimeRange, toDuration: newDuration)

// you can play sloMoComposition in an AVPlayer at this point

// Export to a file using AVAssetExportSession
let exportSession = AVAssetExportSession(asset: sloMoComposition, presetName: AVAssetExportPresetPassthrough)!
exportSession.outputFileType = .mp4
exportSession.outputURL = getDocumentsDirectory().appendingPathComponent("slow-mo-\(Date.timeIntervalSinceReferenceDate).mp4")
exportSession.exportAsynchronously {
    assert(exportSession.status == .completed)
    print("File in \(exportSession.outputURL!)")
}

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