我正在尝试使用 iPhone 的前置摄像头录制带声音的视频。由于我还需要支持暂停/恢复功能，我需要使用AVAssetWriter. 我在网上找到了一个用 Objective-C 编写的示例，它几乎可以实现所需的功能（http://www.gdcl.co.uk/2013/02/20/iPhone-Pause.html）
不幸的是，在将此示例转换为 Swift 之后，我注意到如果我暂停/恢复，在每个“部分”的末尾会有一个小而明显的时间段，在此期间视频只是一个静止帧并且正在播放音频。因此，似乎在isPaused触发时，录制的音轨比录制的视频轨长。
对不起，如果这看起来像一个菜鸟问题，但我不是一个伟大的专家AVFoundation，一些帮助将不胜感激！
下面我发布我的didOutput sampleBuffer.
func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
var isVideo = true
if videoConntection != connection {
isVideo = false
}
if (!isCapturing || isPaused) {
return
}
if (encoder == nil) {
if isVideo {
return
}
if let fmt = CMSampleBufferGetFormatDescription(sampleBuffer) {
let desc = CMAudioFormatDescriptionGetStreamBasicDescription(fmt as CMAudioFormatDescription)
if let chan = desc?.pointee.mChannelsPerFrame, let rate = desc?.pointee.mSampleRate {
let path = tempPath()!
encoder = VideoEncoder(path: path, height: Int(cameraSize.height), width: Int(cameraSize.width), channels: chan, rate: rate)
}
}
}
if discont {
if isVideo {
return
}
discont = false
var pts = CMSampleBufferGetPresentationTimeStamp(sampleBuffer)
let last = lastAudio
if last.flags.contains(CMTimeFlags.valid) {
if cmOffset.flags.contains(CMTimeFlags.valid) {
pts = CMTimeSubtract(pts, cmOffset)
}
let off = CMTimeSubtract(pts, last)
print("setting offset from \(isVideo ? "video":"audio")")
print("adding \(CMTimeGetSeconds(off)) to \(CMTimeGetSeconds(cmOffset)) (pts \(CMTimeGetSeconds(cmOffset)))")
if cmOffset.value == 0 {
cmOffset = off
}
else {
cmOffset = CMTimeAdd(cmOffset, off)
}
}
lastVideo.flags = []
lastAudio.flags = []
return
}
var out:CMSampleBuffer?
if cmOffset.value > 0 {
var count:CMItemCount = CMSampleBufferGetNumSamples(sampleBuffer)
let pInfo = UnsafeMutablePointer<CMSampleTimingInfo>.allocate(capacity: count)
CMSampleBufferGetSampleTimingInfoArray(sampleBuffer, entryCount: count, arrayToFill: pInfo, entriesNeededOut: &count)
var i = 0
while i<count {
pInfo[i].decodeTimeStamp = CMTimeSubtract(pInfo[i].decodeTimeStamp, cmOffset)
pInfo[i].presentationTimeStamp = CMTimeSubtract(pInfo[i].presentationTimeStamp, cmOffset)
i+=1
}
CMSampleBufferCreateCopyWithNewTiming(allocator: nil, sampleBuffer: sampleBuffer, sampleTimingEntryCount: count, sampleTimingArray: pInfo, sampleBufferOut: &out)
}
else {
out = sampleBuffer
}
var pts = CMSampleBufferGetPresentationTimeStamp(out!)
let dur = CMSampleBufferGetDuration(out!)
if (dur.value > 0)
{
pts = CMTimeAdd(pts, dur);
}
if (isVideo) {
lastVideo = pts;
}
else {
lastAudio = pts;
}
encoder?.encodeFrame(sampleBuffer: out!, isVideo: isVideo)
}
这是我的VideoEncoder课：
final class VideoEncoder {
var writer:AVAssetWriter
var videoInput:AVAssetWriterInput
var audioInput:AVAssetWriterInput
var path:String
init(path:String, height:Int, width:Int, channels:UInt32, rate:Float64) {
self.path = path
if FileManager.default.fileExists(atPath:path) {
try? FileManager.default.removeItem(atPath: path)
}
let url = URL(fileURLWithPath: path)
writer = try! AVAssetWriter(outputURL: url, fileType: .mp4)
videoInput = AVAssetWriterInput(mediaType: .video, outputSettings: [
AVVideoCodecKey: AVVideoCodecType.h264,
AVVideoWidthKey:height,
AVVideoHeightKey:width
])
videoInput.expectsMediaDataInRealTime = true
writer.add(videoInput)
audioInput = AVAssetWriterInput(mediaType: .audio, outputSettings: [
AVFormatIDKey:kAudioFormatMPEG4AAC,
AVNumberOfChannelsKey:channels,
AVSampleRateKey:rate
])
audioInput.expectsMediaDataInRealTime = true
writer.add(audioInput)
}
func finish(with completionHandler:@escaping ()->Void) {
writer.finishWriting(completionHandler: completionHandler)
}
func encodeFrame(sampleBuffer:CMSampleBuffer, isVideo:Bool) -> Bool {
if CMSampleBufferDataIsReady(sampleBuffer) {
if writer.status == .unknown {
writer.startWriting()
writer.startSession(atSourceTime: CMSampleBufferGetPresentationTimeStamp(sampleBuffer))
}
if writer.status == .failed {
QFLogger.shared.addLog(format: "[ERROR initiating AVAssetWriter]", args: [], error: writer.error)
return false
}
if isVideo {
if videoInput.isReadyForMoreMediaData {
videoInput.append(sampleBuffer)
return true
}
}
else {
if audioInput.isReadyForMoreMediaData {
audioInput.append(sampleBuffer)
return true
}
}
}
return false
}
}
其余代码应该很明显，但为了使其完整，这是我暂停的内容：
isPaused = true
discont = true
这是简历：
isPaused = false
如果有人可以帮助我了解如何在这种现场录制过程中对齐视频和音轨，那就太好了！