AVFoundataion 音视频采集
2020-03-02 本文已影响0人
pengxiaochao
音视频开发第一章
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1.音频概念
声波的三要素，频率，振幅，波形；
音频通过麦克风转成数字信号才能在互联网上传播，，音频的编码格式有很多种，MP3 ,WAV , ACC ,Ogg 等，但最初的音频裸流数据一般都脉冲编码调制（PCM）数据；采集PCM需要配置以下三个参数，在实际开发中也经常用配置；
- 量化格式(sampleFormat)
- 采样率(sampleRate)
- 声道数(channel)
举例
以CD音质为例,量化格式为16bite,采样率为44100,声道数为2.这些信息描述CD音质.那么可以CD音质数据,比特率是多少?
44100 * 16 * 2 = 1378.125kbps
那么一分钟的,这类CD音质数据需要占用多少存储空间?
1378.125 * 60 /8/1024 = 10.09MB
一般情况下量化格式为8bite 或者16bite，采样率为44100，声道数为1 或者2（表示单声道或者多声道）''
2.1.采集音频数据 （videoToolBox）
//0.创建捕捉会话 AVCaptureSession（音频/视频采集均通过该AVCaptureSession）
self.captureSession = [[AVCaptureSession alloc] init];
//1.获取麦克风设备
AVCaptureDevice *audioDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
//2.设置Audio的input 设备为iphone的麦克风设备
self.audioInputDevice = [AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:nil];
//3.创建音频输出output，并设置AVCaptureAudioDataOutputSampleBufferDelegate 的代理为自己
//self.captureQueue 为自定义队列
self.audioDataOutput = [[AVCaptureAudioDataOutput alloc] init];
[self.audioDataOutput setSampleBufferDelegate:self queue:self.captureQueue];
//4.将音频的input 和output 加入到AVCaptureSession对象中并提交配置
[self.captureSession beginConfiguration];
if ([self.captureSession canAddInput:self.audioInputDevice]) {
[self.captureSession addInput:self.audioInputDevice];
}
if([self.captureSession canAddOutput:self.audioDataOutput]){
[self.captureSession addOutput:self.audioDataOutput];
}
[self.captureSession commitConfiguration];
//self.audioconnection为配置的输出connect对象，可保存在viewcontroller属性中，在代理音频视频的代理方法体中通过connection 判断是音频connect还是视频connection
self.audioConnection = [self.audioDataOutput connectionWithMediaType:AVMediaTypeAudio];
//5.实现AVCaptureAudioDataOutputSampleBufferDelegate 代理方法（捕捉到的音频数据会通过这个sampleBuffer回调出来）
#pragma mark-实现代理方法
-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{
//PCM 数据就存放在 sampleBuffer 对象中；
}
//调用 （开始捕捉音频数据）
[self.captureSession startRunning];
//调用 （停止捕捉音频数据）
[self.captureSession stopRunning];
2.2.编码音频数据
创建一个类 AACAudioEncode 用于将获取到的sampleBuffer 转成AAC 格式的数据；
2.1. 初始化数据
AACAudioEncode类的.h 头文件，通过初始化AudioConfig 配置对象，配置
@protocol AACAudioEncodeDelegate <NSObject>
- (void)audioEncodeCallback:(NSData *)aacData;
@end
@interface AACAudioEncode : NSObject
@property (nonatomic, strong) AudioConfig *config;
@property (nonatomic, weak) id<CCAudioEncoderDelegate> delegate;
/**初始化传入编码器配置*/
- (instancetype)initWithConfig:(AudioConfig*)config;
/**编码*/
- (void)encodeAudioSamepleBuffer: (CMSampleBufferRef)sampleBuffer;
@end
AACAudioEncode 实现细节
- (instancetype)initWithConfig:(AudioConfig*)config {
self = [super init];
if (self) {
_encoderQueue = dispatch_queue_create("aac hard encoder queue", DISPATCH_QUEUE_SERIAL);
_callbackQueue = dispatch_queue_create("aac hard encoder callback queue", DISPATCH_QUEUE_SERIAL);
_audioConverter = NULL;
_pcmBufferSize = 0;
_pcmBuffer = NULL;
_config = config;
if (config == nil) {
_config = [[AudioConfig alloc] init];
}
}
return self;
}
//音频编码(当AVFoundation捕获到音频内容之后)
- (void)encodeAudioSamepleBuffer: (CMSampleBufferRef)sampleBuffer {
CFRetain(sampleBuffer);
//1.判断音频转换器是否创建成功.如果未创建成功.则配置音频编码参数且创建转码器
if (!_audioConverter) {
[self setupEncoderWithSampleBuffer:sampleBuffer];
}
//2.来到音频编码异步队列
dispatch_async(_encoderQueue, ^{
//3.获取CMBlockBuffer, 这里面保存了PCM数据
CMBlockBufferRef blockBuffer = CMSampleBufferGetDataBuffer(sampleBuffer);
CFRetain(blockBuffer);
//4.获取BlockBuffer中音频数据大小以及音频数据地址
OSStatus status = CMBlockBufferGetDataPointer(blockBuffer, 0, NULL, &_pcmBufferSize, &_pcmBuffer);
//5.判断status状态
NSError *error = nil;
if (status != kCMBlockBufferNoErr) {
error = [NSError errorWithDomain:NSOSStatusErrorDomain code:status userInfo:nil];
NSLog(@"Error: ACC encode get data point error: %@",error);
return;
}
//2.设置_aacBuffer 为0
//开辟_pcmBuffsize大小的pcm内存空间
uint8_t *pcmBuffer = malloc(_pcmBufferSize);
//将_pcmBufferSize数据set到pcmBuffer中.
memset(pcmBuffer, 0, _pcmBufferSize);
//3.将pcmBuffer数据填充到outAudioBufferList 对象中
AudioBufferList outAudioBufferList = {0};
outAudioBufferList.mNumberBuffers = 1;
outAudioBufferList.mBuffers[0].mNumberChannels = (uint32_t)_config.channelCount;
outAudioBufferList.mBuffers[0].mDataByteSize = (UInt32)_pcmBufferSize;
outAudioBufferList.mBuffers[0].mData = pcmBuffer;
//设置输出包大小为1
UInt32 outputDataPacketSize = 1;
//配置填充函数，获取输出数据
//转换由输入回调函数提供的数据
/*
参数1: inAudioConverter 音频转换器
参数2: inInputDataProc 回调函数.提供要转换的音频数据的回调函数。当转换器准备好接受新的输入数据时，会重复调用此回调.
参数3: inInputDataProcUserData
参数4: inInputDataProcUserData,self
参数5: ioOutputDataPacketSize,输出缓冲区的大小
参数6: outOutputData,需要转换的音频数据
参数7: outPacketDescription,输出包信息
*/
status = AudioConverterFillComplexBuffer(_audioConverter, aacEncodeInputDataProc, (__bridge void * _Nullable)(self), &outputDataPacketSize, &outAudioBufferList, NULL);
if (status == noErr) {
//获取数据
NSData *rawAAC = [NSData dataWithBytes: outAudioBufferList.mBuffers[0].mData length:outAudioBufferList.mBuffers[0].mDataByteSize];
//释放pcmBuffer
free(pcmBuffer);
//将数据传递到回调队列中
dispatch_async(_callbackQueue, ^{
[_delegate audioEncodeCallback:rawAAC];
});
} else {
error = [NSError errorWithDomain:NSOSStatusErrorDomain code:status userInfo:nil];
}
CFRelease(blockBuffer);
CFRelease(sampleBuffer);
if (error) {
NSLog(@"error: AAC编码失败 %@",error);
}
});
}
//配置音频编码参数
- (void)setupEncoderWithSampleBuffer: (CMSampleBufferRef)sampleBuffer {
//获取输入参数
AudioStreamBasicDescription inputAduioDes = *CMAudioFormatDescriptionGetStreamBasicDescription( CMSampleBufferGetFormatDescription(sampleBuffer));
//设置输出参数
AudioStreamBasicDescription outputAudioDes = {0};
outputAudioDes.mSampleRate = (Float64)_config.sampleRate; //采样率
outputAudioDes.mFormatID = kAudioFormatMPEG4AAC; //输出格式
outputAudioDes.mFormatFlags = kMPEG4Object_AAC_LC; // 如果设为0 代表无损编码
outputAudioDes.mBytesPerPacket = 0; //自己确定每个packet 大小
outputAudioDes.mFramesPerPacket = 1024; //每一个packet帧数 AAC-1024；
outputAudioDes.mBytesPerFrame = 0; //每一帧大小
outputAudioDes.mChannelsPerFrame = (uint32_t)_config.channelCount; //输出声道数
outputAudioDes.mBitsPerChannel = 0; //数据帧中每个通道的采样位数。
outputAudioDes.mReserved = 0; //对其方式 0(8字节对齐)
//填充输出相关信息
UInt32 outDesSize = sizeof(outputAudioDes);
AudioFormatGetProperty(kAudioFormatProperty_FormatInfo, 0, NULL, &outDesSize, &outputAudioDes);
//获取编码器的描述信息(只能传入software)
AudioClassDescription *audioClassDesc = [self getAudioCalssDescriptionWithType:outputAudioDes.mFormatID fromManufacture:kAppleSoftwareAudioCodecManufacturer];
/** 创建converter
参数1：输入音频格式描述
参数2：输出音频格式描述
参数3：class desc的数量
参数4：class desc
参数5：创建的解码器
*/
OSStatus status = AudioConverterNewSpecific(&inputAduioDes, &outputAudioDes, 1, audioClassDesc, &_audioConverter);
if (status != noErr) {
NSLog(@"Error！：硬编码AAC创建失败, status= %d", (int)status);
return;
}
// 设置编解码质量
/*
kAudioConverterQuality_Max = 0x7F,
kAudioConverterQuality_High = 0x60,
kAudioConverterQuality_Medium = 0x40,
kAudioConverterQuality_Low = 0x20,
kAudioConverterQuality_Min = 0
*/
UInt32 temp = kAudioConverterQuality_High;
//编解码器的呈现质量
AudioConverterSetProperty(_audioConverter, kAudioConverterCodecQuality, sizeof(temp), &temp);
//设置比特率
uint32_t audioBitrate = (uint32_t)self.config.bitrate;
uint32_t audioBitrateSize = sizeof(audioBitrate);
status = AudioConverterSetProperty(_audioConverter, kAudioConverterEncodeBitRate, audioBitrateSize, &audioBitrate);
if (status != noErr) {
NSLog(@"Error！：硬编码AAC 设置比特率失败");
}
}
//将sampleBuffer数据提取出PCM数据返回给ViewController.可以直接播放PCM数据
- (NSData *)convertAudioSamepleBufferToPcmData: (CMSampleBufferRef)sampleBuffer {
//获取pcm数据大小
size_t size = CMSampleBufferGetTotalSampleSize(sampleBuffer);
//分配空间
int8_t *audio_data = (int8_t *)malloc(size);
memset(audio_data, 0, size);
//获取CMBlockBuffer, 这里面保存了PCM数据
CMBlockBufferRef blockBuffer = CMSampleBufferGetDataBuffer(sampleBuffer);
//将数据copy到我们分配的空间中
CMBlockBufferCopyDataBytes(blockBuffer, 0, size, audio_data);
NSData *data = [NSData dataWithBytes:audio_data length:size];
free(audio_data);
return data;
}
未完待续......
