这里的目标是通过 AVCaptureDataOutput 的视频和录制 CoreAudio 的音频创建一个 mp4 文件。然后将两者的 CMSampleBuffers 发送到具有随附 AVAssetWriterInput(AVMediaTypeVideo) 和 AVAssetWriterInput(AVMediaTypeAudio) 的 AVAssetWriter
我的音频编码器将 AudioBuffer 复制到新的 CMSampleBuffer 并将其传递给 AVAssetWriterInput(AVMediaTypeAudio)。这个例子是如何完成 AudioBuffer 到 CMSampleBuffer 的转换。转换为 CMSampleBuffer
长话短说，它不起作用。视频显示但没有音频。
但是，如果我注释掉视频编码，那么音频就会被写入文件并且可以听到。
这从经验告诉我这是一个时间问题。到 CMSampleBuffer的转换确实显示
CMSampleTimingInfo timing = { CMTimeMake(1, 44100.0), kCMTimeZero, kCMTimeInvalid };
它产生一个时间 CMTimeCopyDescription ，{0/1 = 0.000} 这对我来说似乎完全错误。我尝试跟踪渲染的帧并传递时间值的帧数和时间尺度的采样率，如下所示
CMSampleTimingInfo timing = { CMTimeMake(1, 44100.0), CMTimeMake(self.frameCount, 44100.0), kCMTimeInvalid };
但没有骰子。更好看的 CMSampleTimingInfo {107520/44100 = 2.438}，但文件中仍然没有音频。
视频 CMSampleBuffer 会产生类似这样的内容{65792640630624/1000000000 = 65792.641, rounded}。这告诉我 AVCaptureVideoOutput 的时间尺度为 10 亿，可能是纳秒。我来宾时间值是设备时间之类的东西。我找不到任何关于 AVCaptureVideoOutput 使用的信息。
有人有任何有用的指导吗？我什至走在正确的轨道上吗？
这是转换
CMSampleBufferRef buff = malloc(sizeof(CMSampleBufferRef));
CMFormatDescriptionRef format = NULL;
self.frameCount += inNumberFrames;
CMTime presentationTime = CMTimeMake(self.frameCount, self.pcmASBD.mSampleRate);
AudioStreamBasicDescription audioFormat = self.pcmASBD;
CheckError(CMAudioFormatDescriptionCreate(kCFAllocatorDefault,
&audioFormat,
0,
NULL,
0,
NULL,
NULL,
&format),
"Could not create format from AudioStreamBasicDescription");
CMSampleTimingInfo timing = { CMTimeMake(1, self.pcmASBD.mSampleRate), presentationTime, kCMTimeInvalid };
CheckError(CMSampleBufferCreate(kCFAllocatorDefault,
NULL,
false,
NULL,
NULL,
format,
(CMItemCount)inNumberFrames,
1,
&timing,
0,
NULL,
&buff),
"Could not create CMSampleBufferRef");
CheckError(CMSampleBufferSetDataBufferFromAudioBufferList(buff,
kCFAllocatorDefault,
kCFAllocatorDefault,
0,
audioBufferList),
"Could not set data in CMSampleBufferRef");
[self.delegate didRenderAudioSampleBuffer:buff];
CFRelease(buff);
还有我创建的assetWriters
func createVideoInputWriter()->AVAssetWriterInput? {
let numPixels = Int(self.size.width * self.size.height)
let bitsPerPixel:Int = 11
let bitRate = Int64(numPixels * bitsPerPixel)
let fps:Int = 30
let settings:[NSObject : AnyObject] = [
AVVideoCodecKey : AVVideoCodecH264,
AVVideoWidthKey : self.size.width,
AVVideoHeightKey : self.size.height,
AVVideoCompressionPropertiesKey : [
AVVideoAverageBitRateKey : NSNumber(longLong: bitRate),
AVVideoMaxKeyFrameIntervalKey : NSNumber(integer: fps)
]
]
var assetWriter:AVAssetWriterInput!
if self.mainAssetWriter.canApplyOutputSettings(settings, forMediaType:AVMediaTypeVideo) {
assetWriter = AVAssetWriterInput(mediaType:AVMediaTypeVideo, outputSettings:settings)
assetWriter.expectsMediaDataInRealTime = true
if self.mainAssetWriter.canAddInput(assetWriter) {
self.mainAssetWriter.addInput(assetWriter)
}
}
return assetWriter;
}
func createAudioInputWriter()->AVAssetWriterInput? {
let settings:[NSObject : AnyObject] = [
AVFormatIDKey : kAudioFormatMPEG4AAC,
AVNumberOfChannelsKey : 2,
AVSampleRateKey : 44100,
AVEncoderBitRateKey : 64000
]
var assetWriter:AVAssetWriterInput!
if self.mainAssetWriter.canApplyOutputSettings(settings, forMediaType:AVMediaTypeAudio) {
assetWriter = AVAssetWriterInput(mediaType:AVMediaTypeAudio, outputSettings:settings)
assetWriter.expectsMediaDataInRealTime = true
if self.mainAssetWriter.canAddInput(assetWriter) {
self.mainAssetWriter.addInput(assetWriter)
} else {
let error = NSError(domain:CMHDFileEncoder.Domain, code:CMHDFileEncoderErrorCode.CantAddInput.rawValue, userInfo:nil)
self.errorDelegate.hdFileEncoderError(error)
}
} else {
let error = NSError(domain:CMHDFileEncoder.Domain, code:CMHDFileEncoderErrorCode.CantApplyOutputSettings.rawValue, userInfo:nil)
self.errorDelegate.hdFileEncoderError(error)
}
return assetWriter
}