在详细回顾了 WWDC2014、Session513 后,我尝试在 IOS8.0 上编写我的应用程序来解码和显示一个实时 H.264 流。首先,我成功构建了H264参数集。当我得到一个带有 4 位起始代码的帧时,就像“0x00 0x00 0x00 0x01 0x65 ...”一样,我将其放入 CMblockBuffer 中。然后我使用预览 CMBlockBuffer 构造一个 CMSampleBuffer。之后,我将 CMSampleBuffer 放入 AVSampleBufferDisplayLayer 中。一切正常(我检查了返回的值),除了 AVSampleBufferDisplayLayer 不显示任何视频图像。由于这些 API 对每个人来说都是相当陌生的,所以我找不到任何机构可以解决这个问题。
我将给出关键代码如下,如果您能帮忙找出视频图像无法显示的原因,我将不胜感激。多谢。
(1)AVSampleBufferDisplayLayer初始化。
dsplayer 是我的主视图控制器的 objc 实例。
@property(nonatomic,strong)AVSampleBufferDisplayLayer *dspLayer;
if(!_dspLayer)
{
_dspLayer = [[AVSampleBufferDisplayLayer alloc]init];
[_dspLayer setFrame:CGRectMake(90,551,557,389)];
_dspLayer.videoGravity = AVLayerVideoGravityResizeAspect;
_dspLayer.backgroundColor = [UIColor grayColor].CGColor;
CMTimebaseRef tmBase = nil;
CMTimebaseCreateWithMasterClock(NULL,CMClockGetHostTimeClock(),&tmBase);
_dspLayer.controlTimebase = tmBase;
CMTimebaseSetTime(_dspLayer.controlTimebase, kCMTimeZero);
CMTimebaseSetRate(_dspLayer.controlTimebase, 1.0);
[self.view.layer addSublayer:_dspLayer];
}
(2)在另一个线程中,我得到一个 H.264 I 帧。
//构造h.264参数集ok
CMVideoFormatDescriptionRef formatDesc;
OSStatus formatCreateResult =
CMVideoFormatDescriptionCreateFromH264ParameterSets(NULL, ppsNum+1, props, sizes, 4, &formatDesc);
NSLog([NSString stringWithFormat:@"construct h264 param set:%ld",formatCreateResult]);
//构造cmBlockbuffer。
//databuf指向H.264数据。以“0x00 0x00 0x00 0x01 0x65 ........”开头
CMBlockBufferRef blockBufferOut = nil;
CMBlockBufferCreateEmpty (0,0,kCMBlockBufferAlwaysCopyDataFlag, &blockBufferOut);
CMBlockBufferAppendMemoryBlock(blockBufferOut,
dataBuf,
dataLen,
NULL,
NULL,
0,
dataLen,
kCMBlockBufferAlwaysCopyDataFlag);
//构造cmsamplebuffer ok
size_t sampleSizeArray[1] = {0};
sampleSizeArray[0] = CMBlockBufferGetDataLength(blockBufferOut);
CMSampleTiminginfo tmInfos[1] = {
{CMTimeMake(5,1), CMTimeMake(5,1), CMTimeMake(5,1)}
};
CMSampleBufferRef sampBuf = nil;
formatCreateResult = CMSampleBufferCreate(kCFAllocatorDefault,
blockBufferOut,
YES,
NULL,
NULL,
formatDesc,
1,
1,
tmInfos,
1,
sampleSizeArray,
&sampBuf);
//放入AVSampleBufferdisplayLayer,仅一帧。但我在视图中看不到任何视频帧
if([self.dspLayer isReadyForMoreMediaData])
{
[self.dspLayer enqueueSampleBuffer:sampBuf];
}
[self.dspLayer setNeedsDisplay];