内容简介：本文主要将含有编码的H.264,H.265视频流文件解码为原始视频数据,解码后即可渲染到屏幕或用作其他用途.正如我们所知,编码数据仅用于传输,无法直接渲染到屏幕上,所以这里利用苹果原生框架VideoToolbox解析文件中的编码的视频流,并将压缩视频数据(h264/h265)解码为指定格式(yuv,RGB)的视频原始数据,以渲染到屏幕上.注意: 本例主要为解码,需要借助FFmpeg搭建模块,视频解析模块,渲染模块,这些模块在下面阅读前提皆有链接可直接访问.
需求
本文主要将含有编码的H.264,H.265视频流文件解码为原始视频数据,解码后即可渲染到屏幕或用作其他用途.
实现原理
正如我们所知,编码数据仅用于传输,无法直接渲染到屏幕上,所以这里利用苹果原生框架VideoToolbox解析文件中的编码的视频流,并将压缩视频数据(h264/h265)解码为指定格式(yuv,RGB)的视频原始数据,以渲染到屏幕上.
注意: 本例主要为解码,需要借助FFmpeg搭建模块,视频解析模块,渲染模块,这些模块在下面阅读前提皆有链接可直接访问.
阅读前提
代码地址 : Video Decoder
掘金地址 : Video Decoder
简书地址 : Video Decoder
博客地址 :Video Decoder
总体架构
总体思想即将FFmpeg parse到的数据装到 CMBlockBuffer 中,将extra data分离出的vps,sps,pps装到 CMVideoFormatDesc 中,将计算好的时间戳装到 CMTime 中,最后即可拼成完成的 CMSampleBuffer 以用来提供给解码器.
简易流程
FFmpeg parse流程
avformat_alloc_context avformat_open_input avformat_find_stream_info formatContext->streams[i]->codecpar->codec_type == (isVideoStream ? AVMEDIA_TYPE_VIDEO : AVMEDIA_TYPE_AUDIO) m_formatContext->streams[m_audioStreamIndex] av_read_frame av_bitstream_filter_filter
VideoToolbox decode流程
- 比较上一次的extra data,如果数据更新需要重新创建解码器
- 分离并保存FFmpeg parse到的extra data中分离vps, sps, pps等关键信息 (比较NALU头)
- 通过
CMVideoFormatDescriptionCreateFromH264ParameterSets,CMVideoFormatDescriptionCreateFromHEVCParameterSets装载vps,sps,pps等NALU header信息. - 指定解码器回调函数与解码后视频数据类型(yuv,RGB…)
- 创建解码器
VTDecompressionSessionCreate - 生成
CMBlockBufferRef装载解码前数据,再将其转为CMSampleBufferRef以提供给解码器. - 开始解码
VTDecompressionSessionDecodeFrame - 在回调函数中
CVImageBufferRef即为解码后的数据,可转为CMSampleBufferRef传出.
文件结构
快速使用
-
初始化preview
解码后的视频数据将渲染到该预览层
- (void)viewDidLoad {
[super viewDidLoad];
[self setupUI];
}
- (void)setupUI {
self.previewView = [[XDXPreviewView alloc] initWithFrame:self.view.frame];
[self.view addSubview:self.previewView];
[self.view bringSubviewToFront:self.startBtn];
}
-
解析并解码文件中视频数据
- (void)startDecodeByVTSessionWithIsH265Data:(BOOL)isH265 { NSString *path = [[NSBundle mainBundle] pathForResource:isH265 ? @"testh265" : @"testh264" ofType:@"MOV"]; XDXAVParseHandler *parseHandler = [[XDXAVParseHandler alloc] initWithPath:path]; XDXVideoDecoder *decoder = [[XDXVideoDecoder alloc] init]; decoder.delegate = self; [parseHandler startParseWithCompletionHandler:^(BOOL isVideoFrame, BOOL isFinish, struct XDXParseVideoDataInfo *videoInfo, struct XDXParseAudioDataInfo *audioInfo) { if (isFinish) { [decoder stopDecoder]; return; } if (isVideoFrame) { [decoder startDecodeVideoData:videoInfo]; } }]; } -
将解码后数据渲染到屏幕上 ()
注意: 如果数据中含有B帧则需要做一个重 排序 才能渲染,本例提供两个文件,一个不含B帧的h264类型文件,一个含B帧的h265类型文件.
- (void)getVideoDecodeDataCallback:(CMSampleBufferRef)sampleBuffer {
if (self.isH265File) {
// Note : the first frame not need to sort.
if (self.isDecodeFirstFrame) {
self.isDecodeFirstFrame = NO;
CVPixelBufferRef pix = CMSampleBufferGetImageBuffer(sampleBuffer);
[self.previewView displayPixelBuffer:pix];
}
XDXSortFrameHandler *sortHandler = [[XDXSortFrameHandler alloc] init];
sortHandler.delegate = self;
[sortHandler addDataToLinkList:sampleBuffer];
}else {
CVPixelBufferRef pix = CMSampleBufferGetImageBuffer(sampleBuffer);
[self.previewView displayPixelBuffer:pix];
}
}
- (void)getSortedVideoNode:(CMSampleBufferRef)sampleBuffer {
int64_t pts = (int64_t)(CMTimeGetSeconds(CMSampleBufferGetPresentationTimeStamp(sampleBuffer)) * 1000);
static int64_t lastpts = 0;
NSLog(@"Test marigin - %lld",pts - lastpts);
lastpts = pts;
[self.previewView displayPixelBuffer:CMSampleBufferGetImageBuffer(sampleBuffer)];
}
具体实现
1. 从Parse到的数据中检测是否需要更新extra data.
使用FFmpeg parse的数据装在 XDXParseVideoDataInfo 结构体中,结构体定义如下,parse模块可在上文链接中学习,本节只将解码模块.
struct XDXParseVideoDataInfo {
uint8_t *data;
int dataSize;
uint8_t *extraData;
int extraDataSize;
Float64 pts;
Float64 time_base;
int videoRotate;
int fps;
CMSampleTimingInfo timingInfo;
XDXVideoEncodeFormat videoFormat;
};
通过缓存当前extra data可以将当前获取的extra data与上一次的进行对比,如果改变需要重新创建解码器,如果没有改变则解码器可复用.(此代码尤其适用于网络流中的视频流,因为视频流可能会改变)
uint8_t *extraData = videoInfo->extraData;
int size = videoInfo->extraDataSize;
BOOL isNeedUpdate = [self isNeedUpdateExtraDataWithNewExtraData:extraData
newSize:size
lastData:&_lastExtraData
lastSize:&_lastExtraDataSize];
......
- (BOOL)isNeedUpdateExtraDataWithNewExtraData:(uint8_t *)newData newSize:(int)newSize lastData:(uint8_t **)lastData lastSize:(int *)lastSize {
BOOL isNeedUpdate = NO;
if (*lastSize == 0) {
isNeedUpdate = YES;
}else {
if (*lastSize != newSize) {
isNeedUpdate = YES;
}else {
if (memcmp(newData, *lastData, newSize) != 0) {
isNeedUpdate = YES;
}
}
}
if (isNeedUpdate) {
[self destoryDecoder];
*lastData = (uint8_t *)malloc(newSize);
memcpy(*lastData, newData, newSize);
*lastSize = newSize;
}
return isNeedUpdate;
}
2. 从extra data中分离关键信息(h265:vps),sps,pps.
创建解码器必须要有NALU Header中的一些关键信息,如vps,sps,pps,以用来组成一个 CMVideoFormatDesc 描述视频信息的数据结构,如上图
注意: h264码流需要sps,pps, h265码流则需要vps,sps,pps
- 分离NALU Header
首先确定start code的位置,通过比较前四个字节是否为 00 00 00 01 即可. 对于h264的数据,start code之后紧接着的是sps,pps, 对于h265的数据则是vps,sps,pps
- 确定NALU Header长度
通过sps索引与pps索引值可以确定sps长度,其他类似,注意,码流结构中均以4个字节的start code作为分界符,所以需要减去对应长度.
- 分离NALU Header数据
对于h264类型数据将数据 & 上 0x1F 可以确定NALU header的类型,对于h265类型数据,将数据 & 上 0x4F 可以确定NALU header的类型,这源于h264,h265的码流结构,如果不懂请参考文章最上方阅读前提中码流结构相关文章.
得到对应类型的数据与大小后,将其赋给全局变量,即可供后面使用.
if (isNeedUpdate) {
log4cplus_error(kModuleName, "%s: update extra data",__func__);
[self getNALUInfoWithVideoFormat:videoInfo->videoFormat
extraData:extraData
extraDataSize:size
decoderInfo:&_decoderInfo];
}
......
- (void)getNALUInfoWithVideoFormat:(XDXVideoEncodeFormat)videoFormat extraData:(uint8_t *)extraData extraDataSize:(int)extraDataSize decoderInfo:(XDXDecoderInfo *)decoderInfo {
uint8_t *data = extraData;
int size = extraDataSize;
int startCodeVPSIndex = 0;
int startCodeSPSIndex = 0;
int startCodeFPPSIndex = 0;
int startCodeRPPSIndex = 0;
int nalu_type = 0;
for (int i = 0; i < size; i ++) {
if (i >= 3) {
if (data[i] == 0x01 && data[i - 1] == 0x00 && data[i - 2] == 0x00 && data[i - 3] == 0x00) {
if (videoFormat == XDXH264EncodeFormat) {
if (startCodeSPSIndex == 0) {
startCodeSPSIndex = i;
}
if (i > startCodeSPSIndex) {
startCodeFPPSIndex = i;
}
}else if (videoFormat == XDXH265EncodeFormat) {
if (startCodeVPSIndex == 0) {
startCodeVPSIndex = i;
continue;
}
if (i > startCodeVPSIndex && startCodeSPSIndex == 0) {
startCodeSPSIndex = i;
continue;
}
if (i > startCodeSPSIndex && startCodeFPPSIndex == 0) {
startCodeFPPSIndex = i;
continue;
}
if (i > startCodeFPPSIndex && startCodeRPPSIndex == 0) {
startCodeRPPSIndex = i;
}
}
}
}
}
int spsSize = startCodeFPPSIndex - startCodeSPSIndex - 4;
decoderInfo->sps_size = spsSize;
if (videoFormat == XDXH264EncodeFormat) {
int f_ppsSize = size - (startCodeFPPSIndex + 1);
decoderInfo->f_pps_size = f_ppsSize;
nalu_type = ((uint8_t)data[startCodeSPSIndex + 1] & 0x1F);
if (nalu_type == 0x07) {
uint8_t *sps = &data[startCodeSPSIndex + 1];
[self copyDataWithOriginDataRef:&decoderInfo->sps newData:sps size:spsSize];
}
nalu_type = ((uint8_t)data[startCodeFPPSIndex + 1] & 0x1F);
if (nalu_type == 0x08) {
uint8_t *pps = &data[startCodeFPPSIndex + 1];
[self copyDataWithOriginDataRef:&decoderInfo->f_pps newData:pps size:f_ppsSize];
}
} else {
int vpsSize = startCodeSPSIndex - startCodeVPSIndex - 4;
decoderInfo->vps_size = vpsSize;
int f_ppsSize = startCodeRPPSIndex - startCodeFPPSIndex - 4;
decoderInfo->f_pps_size = f_ppsSize;
nalu_type = ((uint8_t) data[startCodeVPSIndex + 1] & 0x4F);
if (nalu_type == 0x40) {
uint8_t *vps = &data[startCodeVPSIndex + 1];
[self copyDataWithOriginDataRef:&decoderInfo->vps newData:vps size:vpsSize];
}
nalu_type = ((uint8_t) data[startCodeSPSIndex + 1] & 0x4F);
if (nalu_type == 0x42) {
uint8_t *sps = &data[startCodeSPSIndex + 1];
[self copyDataWithOriginDataRef:&decoderInfo->sps newData:sps size:spsSize];
}
nalu_type = ((uint8_t) data[startCodeFPPSIndex + 1] & 0x4F);
if (nalu_type == 0x44) {
uint8_t *pps = &data[startCodeFPPSIndex + 1];
[self copyDataWithOriginDataRef:&decoderInfo->f_pps newData:pps size:f_ppsSize];
}
if (startCodeRPPSIndex == 0) {
return;
}
int r_ppsSize = size - (startCodeRPPSIndex + 1);
decoderInfo->r_pps_size = r_ppsSize;
nalu_type = ((uint8_t) data[startCodeRPPSIndex + 1] & 0x4F);
if (nalu_type == 0x44) {
uint8_t *pps = &data[startCodeRPPSIndex + 1];
[self copyDataWithOriginDataRef:&decoderInfo->r_pps newData:pps size:r_ppsSize];
}
}
}
- (void)copyDataWithOriginDataRef:(uint8_t **)originDataRef newData:(uint8_t *)newData size:(int)size {
if (*originDataRef) {
free(*originDataRef);
*originDataRef = NULL;
}
*originDataRef = (uint8_t *)malloc(size);
memcpy(*originDataRef, newData, size);
}
3. 创建解码器
根据编码数据类型确定使用h264解码器还是h265解码器,如上图我们可得知,我们需要将数据拼成一个CMSampleBuffer类型以传给解码器解码.
- 生成
CMVideoFormatDescriptionRef
通过(vps)sps,pps信息组成 CMVideoFormatDescriptionRef . 这里需要注意的是, h265编码数据有的码流数据中含有两个pps, 所以在拼装时需要判断以确定参数数量.
- 确定视频数据类型
通过指定 kCVPixelFormatType_420YpCbCr8BiPlanarFullRange 将视频数据类型设置为yuv 420sp, 如需其他格式可自行更改适配.
- 指定回调函数
- 创建编码器
通过上面提供的所有信息,即可调用 VTDecompressionSessionCreate 生成解码器上下文对象.
// create decoder
if (!_decoderSession) {
_decoderSession = [self createDecoderWithVideoInfo:videoInfo
videoDescRef:&_decoderFormatDescription
videoFormat:kCVPixelFormatType_420YpCbCr8BiPlanarFullRange
lock:_decoder_lock
callback:VideoDecoderCallback
decoderInfo:_decoderInfo];
}
- (VTDecompressionSessionRef)createDecoderWithVideoInfo:(XDXParseVideoDataInfo *)videoInfo videoDescRef:(CMVideoFormatDescriptionRef *)videoDescRef videoFormat:(OSType)videoFormat lock:(pthread_mutex_t)lock callback:(VTDecompressionOutputCallback)callback decoderInfo:(XDXDecoderInfo)decoderInfo {
pthread_mutex_lock(&lock);
OSStatus status;
if (videoInfo->videoFormat == XDXH264EncodeFormat) {
const uint8_t *const parameterSetPointers[2] = {decoderInfo.sps, decoderInfo.f_pps};
const size_t parameterSetSizes[2] = {static_cast<size_t>(decoderInfo.sps_size), static_cast<size_t>(decoderInfo.f_pps_size)};
status = CMVideoFormatDescriptionCreateFromH264ParameterSets(kCFAllocatorDefault,
2,
parameterSetPointers,
parameterSetSizes,
4,
videoDescRef);
}else if (videoInfo->videoFormat == XDXH265EncodeFormat) {
if (decoderInfo.r_pps_size == 0) {
const uint8_t *const parameterSetPointers[3] = {decoderInfo.vps, decoderInfo.sps, decoderInfo.f_pps};
const size_t parameterSetSizes[3] = {static_cast<size_t>(decoderInfo.vps_size), static_cast<size_t>(decoderInfo.sps_size), static_cast<size_t>(decoderInfo.f_pps_size)};
if (@available(iOS 11.0, *)) {
status = CMVideoFormatDescriptionCreateFromHEVCParameterSets(kCFAllocatorDefault,
3,
parameterSetPointers,
parameterSetSizes,
4,
NULL,
videoDescRef);
} else {
status = -1;
log4cplus_error(kModuleName, "%s: System version is too low!",__func__);
}
} else {
const uint8_t *const parameterSetPointers[4] = {decoderInfo.vps, decoderInfo.sps, decoderInfo.f_pps, decoderInfo.r_pps};
const size_t parameterSetSizes[4] = {static_cast<size_t>(decoderInfo.vps_size), static_cast<size_t>(decoderInfo.sps_size), static_cast<size_t>(decoderInfo.f_pps_size), static_cast<size_t>(decoderInfo.r_pps_size)};
if (@available(iOS 11.0, *)) {
status = CMVideoFormatDescriptionCreateFromHEVCParameterSets(kCFAllocatorDefault,
4,
parameterSetPointers,
parameterSetSizes,
4,
NULL,
videoDescRef);
} else {
status = -1;
log4cplus_error(kModuleName, "%s: System version is too low!",__func__);
}
}
}else {
status = -1;
}
if (status != noErr) {
log4cplus_error(kModuleName, "%s: NALU header error !",__func__);
pthread_mutex_unlock(&lock);
[self destoryDecoder];
return NULL;
}
uint32_t pixelFormatType = videoFormat;
const void *keys[] = {kCVPixelBufferPixelFormatTypeKey};
const void *values[] = {CFNumberCreate(NULL, kCFNumberSInt32Type, &pixelFormatType)};
CFDictionaryRef attrs = CFDictionaryCreate(NULL, keys, values, 1, NULL, NULL);
VTDecompressionOutputCallbackRecord callBackRecord;
callBackRecord.decompressionOutputCallback = callback;
callBackRecord.decompressionOutputRefCon = (__bridge void *)self;
VTDecompressionSessionRef session;
status = VTDecompressionSessionCreate(kCFAllocatorDefault,
*videoDescRef,
NULL,
attrs,
&callBackRecord,
&session);
CFRelease(attrs);
pthread_mutex_unlock(&lock);
if (status != noErr) {
log4cplus_error(kModuleName, "%s: Create decoder failed",__func__);
[self destoryDecoder];
return NULL;
}
return session;
}
4. 开始解码
- 将parse出来的原始数据装在
XDXDecodeVideoInfo结构体中,以便后续扩展使用.
typedef struct {
CVPixelBufferRef outputPixelbuffer;
int rotate;
Float64 pts;
int fps;
int source_index;
} XDXDecodeVideoInfo;
- 将编码数据装在
CMBlockBufferRef中. - 通过
CMBlockBufferRef生成CMSampleBufferRef - 解码数据
通过 VTDecompressionSessionDecodeFrame 函数即可完成解码一帧视频数据.第三个参数可以指定解码采用同步或异步方式.
// start decode
[self startDecode:videoInfo
session:_decoderSession
lock:_decoder_lock];
......
- (void)startDecode:(XDXParseVideoDataInfo *)videoInfo session:(VTDecompressionSessionRef)session lock:(pthread_mutex_t)lock {
pthread_mutex_lock(&lock);
uint8_t *data = videoInfo->data;
int size = videoInfo->dataSize;
int rotate = videoInfo->videoRotate;
CMSampleTimingInfo timingInfo = videoInfo->timingInfo;
uint8_t *tempData = (uint8_t *)malloc(size);
memcpy(tempData, data, size);
XDXDecodeVideoInfo *sourceRef = (XDXDecodeVideoInfo *)malloc(sizeof(XDXParseVideoDataInfo));
sourceRef->outputPixelbuffer = NULL;
sourceRef->rotate = rotate;
sourceRef->pts = videoInfo->pts;
sourceRef->fps = videoInfo->fps;
CMBlockBufferRef blockBuffer;
OSStatus status = CMBlockBufferCreateWithMemoryBlock(kCFAllocatorDefault,
(void *)tempData,
size,
kCFAllocatorNull,
NULL,
0,
size,
0,
&blockBuffer);
if (status == kCMBlockBufferNoErr) {
CMSampleBufferRef sampleBuffer = NULL;
const size_t sampleSizeArray[] = { static_cast<size_t>(size) };
status = CMSampleBufferCreateReady(kCFAllocatorDefault,
blockBuffer,
_decoderFormatDescription,
1,
1,
&timingInfo,
1,
sampleSizeArray,
&sampleBuffer);
if (status == kCMBlockBufferNoErr && sampleBuffer) {
VTDecodeFrameFlags flags = kVTDecodeFrame_EnableAsynchronousDecompression;
VTDecodeInfoFlags flagOut = 0;
OSStatus decodeStatus = VTDecompressionSessionDecodeFrame(session,
sampleBuffer,
flags,
sourceRef,
&flagOut);
if(decodeStatus == kVTInvalidSessionErr) {
pthread_mutex_unlock(&lock);
[self destoryDecoder];
if (blockBuffer)
CFRelease(blockBuffer);
free(tempData);
tempData = NULL;
CFRelease(sampleBuffer);
return;
}
CFRelease(sampleBuffer);
}
}
if (blockBuffer) {
CFRelease(blockBuffer);
}
free(tempData);
tempData = NULL;
pthread_mutex_unlock(&lock);
}
5. 解码后的数据
解码后的数据可在回调函数中获取.这里需要将解码后的数据 CVImageBufferRef 转为 CMSampleBufferRef .然后通过代理传出.
#pragma mark - Callback
static void VideoDecoderCallback(void *decompressionOutputRefCon, void *sourceFrameRefCon, OSStatus status, VTDecodeInfoFlags infoFlags, CVImageBufferRef pixelBuffer, CMTime presentationTimeStamp, CMTime presentationDuration) {
XDXDecodeVideoInfo *sourceRef = (XDXDecodeVideoInfo *)sourceFrameRefCon;
if (pixelBuffer == NULL) {
log4cplus_error(kModuleName, "%s: pixelbuffer is NULL status = %d",__func__,status);
if (sourceRef) {
free(sourceRef);
}
return;
}
XDXVideoDecoder *decoder = (__bridge XDXVideoDecoder *)decompressionOutputRefCon;
CMSampleTimingInfo sampleTime = {
.presentationTimeStamp = presentationTimeStamp,
.decodeTimeStamp = presentationTimeStamp
};
CMSampleBufferRef samplebuffer = [decoder createSampleBufferFromPixelbuffer:pixelBuffer
videoRotate:sourceRef->rotate
timingInfo:sampleTime];
if (samplebuffer) {
if ([decoder.delegate respondsToSelector:@selector(getVideoDecodeDataCallback:)]) {
[decoder.delegate getVideoDecodeDataCallback:samplebuffer];
}
CFRelease(samplebuffer);
}
if (sourceRef) {
free(sourceRef);
}
}
- (CMSampleBufferRef)createSampleBufferFromPixelbuffer:(CVImageBufferRef)pixelBuffer videoRotate:(int)videoRotate timingInfo:(CMSampleTimingInfo)timingInfo {
if (!pixelBuffer) {
return NULL;
}
CVPixelBufferRef final_pixelbuffer = pixelBuffer;
CMSampleBufferRef samplebuffer = NULL;
CMVideoFormatDescriptionRef videoInfo = NULL;
OSStatus status = CMVideoFormatDescriptionCreateForImageBuffer(kCFAllocatorDefault, final_pixelbuffer, &videoInfo);
status = CMSampleBufferCreateForImageBuffer(kCFAllocatorDefault, final_pixelbuffer, true, NULL, NULL, videoInfo, &timingInfo, &samplebuffer);
if (videoInfo != NULL) {
CFRelease(videoInfo);
}
if (samplebuffer == NULL || status != noErr) {
return NULL;
}
return samplebuffer;
}
6.销毁解码器
用完后记得销毁,以便下次使用.
if (_decoderSession) {
VTDecompressionSessionWaitForAsynchronousFrames(_decoderSession);
VTDecompressionSessionInvalidate(_decoderSession);
CFRelease(_decoderSession);
_decoderSession = NULL;
}
if (_decoderFormatDescription) {
CFRelease(_decoderFormatDescription);
_decoderFormatDescription = NULL;
}
7. 补充:关于带B帧数据重排序问题
注意,如果视频文件或视频流中含有B帧,则渲染时需要对视频帧做一个重排序,本文重点讲解码,排序将在后面文章中更新,代码中以实现,如需了解请下载Demo.
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持 码农网
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