引言
从iOS8开始，苹果将VideoToolbox.framework开放了出来，使开发者可以使用iOS设备内置的硬件设备来进行视频的编码和解码工作。硬件编解码的好处是，复杂的计算由专门的硬件电路完成，往往比使用cpu计算更高效，速度更快，功耗也更低。H.264是目前很流行的编码层视频压缩格式，目前项目中的协议层有rtmp与http，但是视频的编码层都是使用的H.264。
关于H.264编码格式相关知识请看深入浅出理解视频编码H264结构本篇不再赘述。在iOS平台上对视频数据进行H.264编码有两种方式：
- 软件编码：用ffmpeg等开源库进行编码，他是用cpu进行相关计算的，效率比较低，但是比较通用，是跨平台的。
- 硬件编码：用VideoToolbox今天编码，他是用GPU进行相关计算的，效率很高。
在熟悉H.264的过程中，为更好的了解H.264，尝试用VideoToolbox硬编码与硬解码H.264的原始码流。
今天我们主要来看看使用VideoToolbox硬编码H.264。
用VideoToolbox硬编码H.264步骤如下：
初始化摄像头，output设定的时候，需要设置delegate和输出队列。在delegate方法，处理采集好的图像。
初始化VideoToolbox，设置各种属性。
获取每一帧数并编码。
每一帧数据编码完成后，在回调方法中判断是不是关键帧，如果是关键帧需要用CMSampleBufferGetFormatDescription获取CMFormatDescriptionRef，然后用
CMVideoFormatDescriptionGetH264ParameterSetAtIndex取得PPS和SPS；最后把每一帧的所有NALU数据前四个字节变成0x00 00 00 01之后再写入文件。循环步骤3步骤4。
调用VTCompressionSessionCompleteFrames完成编码，然后销毁session：VTCompressionSessionInvalidate，释放session。
详细代码
//
// AVVideoToolBoxh264VC.m
// AudioandVideo
//
// Created by sunpeng on 17/1/10.
// Copyright © 2017年 mac. All rights reserved.
//
#import "AVVideoToolBoxh264VC.h"
#import <AVFoundation/AVFoundation.h>
#import <AVFoundation/AVCaptureOutput.h>
#import <AssetsLibrary/AssetsLibrary.h>
#import <VideoToolbox/VideoToolbox.h>
@interface AVVideoToolBoxh264VC ()<AVCaptureVideoDataOutputSampleBufferDelegate> {
int frameID;
NSFileHandle *fileHandle;
dispatch_queue_t encodeQueue;
VTCompressionSessionRef encodingSession;
CMFormatDescriptionRef format;
}
//camera
@property (nonatomic, strong) AVCaptureSession * captureSession;
@property (nonatomic, strong) AVCaptureDeviceInput * captureDeviceInput;
@property (nonatomic, strong) AVCaptureStillImageOutput * captureImageOutput;
@property (nonatomic, strong) AVCaptureMovieFileOutput * captureMovieFileOutput;
@property (nonatomic, strong) AVCaptureVideoPreviewLayer * captureVideoPreLayer;
@end
@implementation AVVideoToolBoxh264VC
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
self.view.backgroundColor = [UIColor whiteColor];
self.title = @"使用VideoToolbox硬编码H.264";
[self initCamera];
[self initVideoToolBox];
[self.captureSession startRunning];
}
- (void)viewWillDisappear:(BOOL)animated{
[super viewWillDisappear:animated];
[self.captureSession stopRunning];
[self endVodeoToolBox];
}
- (void)initCamera{
//创建回话
_captureSession = [[AVCaptureSession alloc] init];
if ([_captureSession canSetSessionPreset:AVCaptureSessionPreset1280x720]) {
_captureSession.sessionPreset = AVCaptureSessionPreset1280x720;
}
AVCaptureDevice * captureDevice = [self getCameraDeviceWithPosition:AVCaptureDevicePositionBack];
if (!captureDevice) {
NSLog(@"获取后置摄像头失败");
return;
}
NSError * error = nil;
_captureDeviceInput = [[AVCaptureDeviceInput alloc] initWithDevice:captureDevice error:&error];
if (error) {
NSLog(@"获取输入设备出错--%@",error.localizedDescription);
return;
}
// //将设备输入添加到回话中
if ([_captureSession canAddInput:_captureDeviceInput]) {
[_captureSession addInput:_captureDeviceInput];
AVCaptureConnection *captureConnection=[_captureMovieFileOutput connectionWithMediaType:AVMediaTypeVideo];
if ([captureConnection isVideoStabilizationSupported ]) {
captureConnection.preferredVideoStabilizationMode=AVCaptureVideoStabilizationModeAuto;
}
}
//创建输出设备并添加到回话中
AVCaptureVideoDataOutput * output = [[AVCaptureVideoDataOutput alloc] init];
[_captureSession addOutput:output];
dispatch_queue_t queue = dispatch_queue_create("myQueue", NULL);
[output setSampleBufferDelegate:self queue:queue];
output.videoSettings = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey];
//创建视频预览层，用于实时展示摄像头状态
_captureVideoPreLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:_captureSession];
CALayer * layer = self.view.layer;
layer.masksToBounds = YES;
_captureVideoPreLayer.frame = layer.bounds;
_captureVideoPreLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
[self.view.layer addSublayer:_captureVideoPreLayer];
NSString *file = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"abc.h264"];
[[NSFileManager defaultManager] removeItemAtPath:file error:nil];
[[NSFileManager defaultManager] createFileAtPath:file contents:nil attributes:nil];
fileHandle = [NSFileHandle fileHandleForWritingAtPath:file];
}
//获取摄像头
- (AVCaptureDevice *)getCameraDeviceWithPosition:(AVCaptureDevicePosition) position{
NSArray * cameras = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
for (AVCaptureDevice * camera in cameras) {
if ([camera position] == position) {
return camera;
}
}
return nil;
}
//初始化videoToolBox
- (void)initVideoToolBox{
encodeQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_sync(encodeQueue, ^{
frameID = 0;
int Width = 1280, height = 720;
//创建编码回话 encodedPerFrameH264 是编码一帧数据后的回调方法
OSStatus status = VTCompressionSessionCreate(NULL, Width, height, kCMVideoCodecType_H264, NULL, NULL, NULL, encodedPerFrameH264, (__bridge void * )(self), &encodingSession);
NSLog(@"H264: VTCompressionSessionCreate %d", (int)status);
if (status != 0) {
NSLog(@"H264: unable to create a H264 Session");
return ;
}
//-----------------------------------------设置编码会话各种属性
//设置实时编码输出 ，避免延迟
VTSessionSetProperty(encodingSession, kVTCompressionPropertyKey_RealTime, kCFBooleanTrue);
VTSessionSetProperty(encodingSession, kVTCompressionPropertyKey_ProfileLevel, kVTProfileLevel_H264_Baseline_AutoLevel);
//设置关键帧间隔(GOPsize)
int frameInterval = 10;
CFNumberRef frameIntervalRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &frameInterval);
VTSessionSetProperty(encodingSession, kVTCompressionPropertyKey_MaxKeyFrameInterval, frameIntervalRef);
//设置期望帧率
int fps = 10;
CFNumberRef fpsRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &fps);
VTSessionSetProperty(encodingSession, kVTCompressionPropertyKey_ExpectedFrameRate, fpsRef);
//设置码率， 上限， 单位是bps
int bitRate = Width * height * 3 * 4 * 8;
CFNumberRef bitRateRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &bitRate);
VTSessionSetProperty(encodingSession, kVTCompressionPropertyKey_AverageBitRate, bitRateRef);
//设置码率， 均值，单位是byte
int bitRateLimit = Width * height * 3 * 4;
CFNumberRef bitRateLimitRef = CFNumberCreate(kCFAllocatorDefault , kCFNumberSInt32Type, &bitRateLimit);
VTSessionSetProperty(encodingSession, kVTCompressionPropertyKey_DataRateLimits, bitRateLimitRef);
//tell the encoder to start encoding
VTCompressionSessionPrepareToEncodeFrames(encodingSession);
});
}
//编码一帧原始图像
- (void)encodePerFrame:(CMSampleBufferRef) sampleBuffer{
CVImageBufferRef imageBuffer = (CVImageBufferRef)CMSampleBufferGetImageBuffer(sampleBuffer);
//帧世界，如果不设置会导致时间轴过长
CMTime presentationTimeStamp = CMTimeMake(frameID++, 1000);
VTEncodeInfoFlags flags;
//编码
OSStatus statusCode = VTCompressionSessionEncodeFrame(encodingSession, imageBuffer, presentationTimeStamp, kCMTimeInvalid, NULL, NULL, &flags);
if (statusCode != noErr) {
NSLog(@"H264: VTCompressionSessionEncodeFrame failed with %d", (int) statusCode);
VTCompressionSessionInvalidate(encodingSession);
CFRelease(encodingSession);
encodingSession = NULL;
return;
}
NSLog(@"H264: VTCompressionSessionEncodeFrame Success");
}
//编码一帧后到回调方法
void encodedPerFrameH264(void * outputCallbackRefCon, void * sourceFrameRefCon, OSStatus status, VTEncodeInfoFlags infoFlags, CMSampleBufferRef sampleBuffer){
NSLog(@"encodedPerFrameH264 called with status %d infoFlags %d", (int)status, (int)infoFlags);
if (status != 0) {
return;
}
if (!CMSampleBufferDataIsReady(sampleBuffer)) {
NSLog(@"encodedPerFrameH264 data is not ready");
return;
}
AVVideoToolBoxh264VC * encoder = (__bridge AVVideoToolBoxh264VC *)outputCallbackRefCon;
bool keyframe = !CFDictionaryContainsKey((CFArrayGetValueAtIndex(CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, true), 0) ), kCMSampleAttachmentKey_NotSync);
//判断当前帧是否为关键帧
if (keyframe) {
CMFormatDescriptionRef format = CMSampleBufferGetFormatDescription(sampleBuffer);
size_t sparameterSetSize, sparameterSetCount;
const uint8_t * sparameterSet;
OSStatus statusCode = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(format, 0, &sparameterSet, &sparameterSetSize, &sparameterSetCount, 0);
if (statusCode == noErr) {
size_t pparameterSetSize, pparameterSetCount;
const uint8_t * pparameterSet;
OSStatus statusCode = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(format, 1, &pparameterSet, &pparameterSetSize, &pparameterSetCount, 0);
if (statusCode == noErr) {
//found pps
NSData * sps = [NSData dataWithBytes:sparameterSet length:sparameterSetSize];
NSData * pps = [NSData dataWithBytes:pparameterSet length:pparameterSetSize];
if (encoder) {
[encoder setSpsAndPps:sps pps:pps];
}
}
}
}
CMBlockBufferRef dataBuffer = CMSampleBufferGetDataBuffer(sampleBuffer);
size_t length , totalLength;
char * dataPointer;
OSStatus statusCodeRet = CMBlockBufferGetDataPointer(dataBuffer, 0, &length, &totalLength, &dataPointer);
if (statusCodeRet == noErr) {
size_t bufferOffset = 0;
// 返回的nalu数据前四个字节不是0001的startcode，而是大端模式的帧长度length
static const int AVCCHeaderLength = 4;
//循环获取nalu 数据
while (bufferOffset < totalLength - AVCCHeaderLength) {
uint32_t NALUnitLength = 0;
// Read the NAL unit length
memcpy(&NALUnitLength, dataPointer + bufferOffset, AVCCHeaderLength);
// 从大端转系统端
NALUnitLength = CFSwapInt32BigToHost(NALUnitLength);
NSData* data = [[NSData alloc] initWithBytes:(dataPointer + bufferOffset + AVCCHeaderLength) length:NALUnitLength];
[encoder setEncodedData:data isKeyFrame:keyframe];
// Move to the next NAL unit in the block buffer
bufferOffset += AVCCHeaderLength + NALUnitLength;
}
}
}
//设置sps pps
- (void)setSpsAndPps:(NSData *) sps pps: (NSData *) pps{
NSLog(@"setSpsAndPps %d %d", (int)[sps length], (int)[pps length] );
const char bytes[] = "\x00\x00\x00\x01";
//string literals hava implicit trailing '\0'
size_t length = (sizeof(bytes) - 1);
NSData * ByteHeader = [NSData dataWithBytes:bytes length:length];
[fileHandle writeData:ByteHeader];
[fileHandle writeData:sps];
[fileHandle writeData:ByteHeader];
[fileHandle writeData:pps];
}
//写入一帧编码过后的数据到文件
- (void)setEncodedData: (NSData *)data isKeyFrame:(BOOL) isKeyFrame{
NSLog(@"setEncodedData %d", (int)[data length]);
if (fileHandle != NULL) {
const char bytes[] = "\x00\x00\x00\x01";
//string literals hava implicit trailing '\0'
size_t length = (sizeof(bytes) -1);
NSData * ByteHeader = [NSData dataWithBytes:bytes length:length];
[fileHandle writeData:ByteHeader];
[fileHandle writeData:data];
}
}
- (void)endVodeoToolBox{
VTCompressionSessionCompleteFrames(encodingSession, kCMTimeInvalid);
VTCompressionSessionInvalidate(encodingSession);
CFRelease(encodingSession);
encodingSession = NULL;
}
#pragma mark - AVCaptureFileOutputDelegate//获取视频流中每一帧数据（图片）
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{
dispatch_sync(encodeQueue, ^{
[self encodePerFrame:sampleBuffer];
});
}
@end
未完待续
