网络摄像头拉流
1.接收视频数据
1.1结构体
1.1.1编码基本单位NALU
// NALU
typedef struct _MP4ENC_NaluUnit
{
int type;
int size;
unsigned char *data;
}MP4ENC_NaluUnit;
/**
* rational number numerator/denominator
*/
typedef struct AVRational{
int num; ///< numerator
int den; ///< denominator
} AVRational;
AVRational这个结构标识一个分数,num为分数,den为分母。
实际上time_base的意思就是时间的刻度:
如(1,25),那么时间刻度就是1/25; (1,90000),那么时间刻度就是1/90000
那么,在刻度为1/25的体系下的time=5,转换成在刻度为1/90000体系下的时间time为(51/25)/(1/90000) = 36005=18000
ffmpeg中做pts计算时,存在大量这种转换
在以下结构中都有
AVCodecContext:编解码上下文。
AVStream:文件或其它容器中的某一个track。
如果由某个解码器产生固定帧率的码流
AVCodecContext中的AVRational根据帧率来设定,如25帧,那么num = 1,den=25
AVStream中的time_base一般根据其采样频率设定,如(1,90000)
在某些场景下涉及到PTS的计算时,就涉及到两个Time的转换,以及到底取哪里的time_base进行转换:
场景1:编码器产生的帧,直接存入某个容器的AVStream中,那么此时packet的Time要从AVCodecContext的time转换成目标AVStream的time
场景2:从一种容器中demux出来的源AVStream的frame,存入另一个容器中某个目的AVStream。此时的时间刻度应该从源AVStream的time,转换成目的AVStream timebase下的时间。
其实,问题的关键还是要理解,不同的场景下取到的数据帧的time是相对哪个时间体系的。
demux出来的帧的time:是相对于源AVStream的timebase
编码器出来的帧的time:是相对于源AVCodecContext的timebase
mux存入文件等容器的time:是相对于目的AVStream的timebase
这里的time指pts。
http://blog.csdn.net/peckjerry/article/details/48344389
1.1.3录像文件信息RecordInfo
typedef struct tag_RECORD_INFO
{
int m_nCurPts; //当前位置的pts pts presentation time stamp 度量解码后的视频帧什么时候被显示出来
double m_dCurTime; //当前位置的时间(没有使用)
uint m_nTotalTime; //总时长
uint m_nLastTimestamp; //上一个位置的时间戳
}RecordInfo;
1.1.4 时间计时器
//时间计时器
unsigned int _getTickCount() {
struct timeval tv;
//gettimeofday 获取当前精确时间
/*
int gettimeofday(struct timeval*tv, struct timezone *tz);
其参数tv是保存获取时间结果的结构体,参数tz用于保存时区结果:
struct timezone{
int tz_minuteswest;//格林威治时间往西方的时差
int tz_dsttime;DST //时间的修正方式
}
timezone 参数若不使用则传入NULL即可。
*/
if (gettimeofday(&tv, NULL) != 0)
return 0;
return (tv.tv_sec * 1000 + tv.tv_usec / 1000);
}
1.2属性
1.2.1 MP4VideoRecorder的属性
@interface Mp4VideoRecorder : NSObject
{
bool m_bRecord; //录像状态
NSString* m_strRecordFile; //录像文件存放路径
int m_nFileTotalSize; //文件总大小
RecordInfo m_stFrameInfo; //视频信息
RecordInfo m_stAudioInfo; //音频信息
AVStream *m_pVideoSt; //视频
AVStream *m_pAudioSt; //音频
AVFormatContext *m_pFormatCtx;
int m_nWidth;
int m_nHeight;
int m_nFrameRate;
double startTimeStamp;
int firstIFrame_states;
int startRecord_states;
MP4_RecordAvccBox m_avcCBox;
AACEncodeConfig* g_aacEncodeConfig;
int g_writeRemainSize;
int g_bufferRemainSize;
NSLock* videoLock;
}
1.2核心代码
- (void)doRecvVideo
{
int readSize = -1;
char *recvBuf = malloc(RECV_VIDEO_BUFFER_SIZE);
FRAMEINFO_t frmInfo = {0};
unsigned int frmNo = 0,prevFrmNo=0x0FFFFFFF;
int outBufSize = 0, outFrmSize = 0, outFrmInfoSize = 0;
H264Decoder* decoder=[[H264Decoder alloc] init];
decoder.updateDelegate=self;
unsigned int timestamp=_getTickCount();
int videoBps=0;
if (sessionID >= 0 && avIndex >= 0)
{
avClientCleanVideoBuf(avIndex);
while (isRunningRecvVideoThread)
{
unsigned int now = _getTickCount();
if (now - timestamp > 1000)
{
dispatch_async(dispatch_get_main_queue(), ^{
if (self.cameraDelegate &&[self.cameraDelegate respondsToSelector:@selector(camera:frameInfoWithVideoBPS:)])
{
[self.cameraDelegate camera:self frameInfoWithVideoBPS:videoBps];
}
});
timestamp = now;
videoBps = 0;
}
//usleep(1*1000);
readSize = avRecvFrameData2(avIndex, recvBuf, RECV_VIDEO_BUFFER_SIZE, &outBufSize, &outFrmSize, (char *)&frmInfo, sizeof(frmInfo), &outFrmInfoSize, &frmNo);
if (readSize == AV_ER_BUFPARA_MAXSIZE_INSUFF)
{
continue;
}else if (readSize == AV_ER_MEM_INSUFF)
{
continue;
} else if(readSize == AV_ER_INCOMPLETE_FRAME)
{
continue;
}
else if (readSize == AV_ER_LOSED_THIS_FRAME)
{
continue;
}
else if (readSize == AV_ER_DATA_NOREADY)
{
usleep(10*1000);
continue;
}
else if (readSize >= 0)
{
if (frmInfo.flags == IPC_FRAME_FLAG_IFRAME || frmNo == (prevFrmNo + 1))
{
prevFrmNo = frmNo;
if (frmInfo.codec_id == MEDIA_CODEC_VIDEO_H264)
{
//printf("RECV H.264 ======================size: %d\n",readSize);
[[Mp4VideoRecorder getInstance] writeFrameData:(unsigned char *)recvBuf withSize:readSize];
[decoder DecodeH264Frames:(unsigned char*)recvBuf withLength:readSize];
}
videoBps+=readSize;
}
else
{
NSLog(@"\t[H264] Incorrect %@ frame no(%d), prev:%d -> drop frame", (frmInfo.flags == IPC_FRAME_FLAG_IFRAME ? @"I" : @"P"), frmNo, prevFrmNo);
usleep(1*1000);
continue;
}
}
else
{
usleep(1*1000);
continue;
}
}
}
else
{
free(recvBuf);
decoder.updateDelegate=nil;
[decoder release];
printf("doRecvVideo: [sessionID < 0 || avIndex < 0]\n");
return;
}
free(recvBuf);
decoder.updateDelegate=nil;
[decoder release];
NSLog(@"\t=== RecvVideo Thread Exit ===\n");
}
2.写入视频
- (void)writeFrameData: (unsigned char *)pszData withSize: (int)aSize
{
if (!m_bRecord)
{
return;
}
if(aSize<=4){
return;
}
MP4ENC_NaluUnit nalu;
memset(&nalu, 0, sizeof(nalu));
int len = 0;
int pos = 0;
memset(&m_avcCBox, 0, sizeof(m_avcCBox));
memset(m_avcCBox.ppsBuffer, 0, sizeof(m_avcCBox.ppsBuffer));
memset(m_avcCBox.spsBuffer, 0, sizeof(m_avcCBox.spsBuffer));
while ((len = [self readOneNaluFromBuffer:pszData withSize:aSize withOffSet:pos nalUnit: &nalu]))
{
if(nalu.type==0x07)//SPS
{
if(nalu.size>0){
memcpy(m_avcCBox.spsBuffer, nalu.data, nalu.size);
m_avcCBox.sps_length=nalu.size;
}
firstIFrame_states = 1;
}
if(nalu.type==0x08)//PPS
{
if(nalu.size>0){
memcpy(m_avcCBox.ppsBuffer, nalu.data, nalu.size);
m_avcCBox.pps_length=nalu.size;
}
}
if(firstIFrame_states!=1){
printf("NO_SPS_RETURN: \n");//获取第一个I帧. 否则就直接返回.
startTimeStamp=[self _GetTickCount];
pos += len;
continue ;
}
if(nalu.type == 0x05) //i帧
{
FrameData *pFrameData=(FrameData *)malloc(sizeof(FrameData));
memset(pFrameData, 0, sizeof(FrameData));
int datalen = nalu.size+4;
unsigned char *pData =(unsigned char *) malloc( datalen * sizeof(unsigned char));
// MP4 Nalu前四个字节表示Nalu长度
pData[0] = nalu.size>>24;
pData[1] = nalu.size>>16;
pData[2] = nalu.size>>8;
pData[3] = nalu.size&0xff;
memcpy(pData+4,nalu.data,nalu.size);
pFrameData->m_nSize = datalen;
memcpy(pFrameData->m_pszData, pData, datalen);
pFrameData->m_nCodecID = CODEC_ID_H264;
pFrameData->m_nTimestamp = [self _GetTickCount]-startTimeStamp;
[self WriteVideoSt:pFrameData withKeyFlags:1];
free(pFrameData);
free(pData);
}
else if(nalu.type == 0x01)//
{
FrameData *pFrameData=(FrameData *)malloc(sizeof(FrameData));
memset(pFrameData, 0, sizeof(FrameData));
int datalen = nalu.size+4;
unsigned char *pData =(unsigned char *) malloc( datalen * sizeof(unsigned char));
// MP4 Nalu前四个字节表示Nalu长度
pData[0] = nalu.size>>24;
pData[1] = nalu.size>>16;
pData[2] = nalu.size>>8;
pData[3] = nalu.size&0xff;
memcpy(pData+4,nalu.data,nalu.size);
pFrameData->m_nSize = datalen;
memcpy(pFrameData->m_pszData, pData, datalen);
pFrameData->m_nCodecID = CODEC_ID_H264;
pFrameData->m_nTimestamp = [self _GetTickCount]-startTimeStamp;
[self WriteVideoSt:pFrameData withKeyFlags:0];
free(pFrameData);
free(pData);
}
pos += len;
}
}
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