Decoding H264 VideoToolkit API fails with Error -12911 in VTDecompressionSessionDecodeFrame - ios

Question

I'm trying to decode a raw stream of .H264 video data but I can't find a way to create a proper
- (void)decodeFrameWithNSData:(NSData*)data presentationTime:
(CMTime)presentationTime
{
#autoreleasepool {
CMSampleBufferRef sampleBuffer = NULL;
CMBlockBufferRef blockBuffer = NULL;
VTDecodeInfoFlags infoFlags;
int sourceFrame;
if( dSessionRef == NULL )
[self createDecompressionSession];
CMSampleTimingInfo timingInfo ;
timingInfo.presentationTimeStamp = presentationTime;
timingInfo.duration = CMTimeMake(1,100000000);
timingInfo.decodeTimeStamp = kCMTimeInvalid;
//Creates block buffer from NSData
OSStatus status = CMBlockBufferCreateWithMemoryBlock(CFAllocatorGetDefault(), (void*)data.bytes,data.length*sizeof(char), CFAllocatorGetDefault(), NULL, 0, data.length*sizeof(char), 0, &blockBuffer);
//Creates CMSampleBuffer to feed decompression session
status = CMSampleBufferCreateReady(CFAllocatorGetDefault(), blockBuffer,self.encoderVideoFormat,1,1,&timingInfo, 0, 0, &sampleBuffer);
status = VTDecompressionSessionDecodeFrame(dSessionRef,sampleBuffer, kVTDecodeFrame_1xRealTimePlayback, &sourceFrame,&infoFlags);
if(status != noErr) {
NSLog(#"Decode with data error %d",status);
}
}
}
At the end of the call I'm getting -12911 error in VTDecompressionSessionDecodeFrame that translates to kVTVideoDecoderMalfunctionErr which after reading this [post] pointed me that I should make a VideoFormatDescriptor using CMVideoFormatDescriptionCreateFromH264ParameterSets. But how can I create a new VideoFormatDescription if I don't have information of the currentSps or currentPps? How can I get that information from my raw .H264 streaming?
CMFormatDescriptionRef decoderFormatDescription;
const uint8_t* const parameterSetPointers[2] =
{ (const uint8_t*)[currentSps bytes], (const uint8_t*)[currentPps bytes] };
const size_t parameterSetSizes[2] =
{ [currentSps length], [currentPps length] };
status = CMVideoFormatDescriptionCreateFromH264ParameterSets(NULL,
2,
parameterSetPointers,
parameterSetSizes,
4,
&decoderFormatDescription);
Thanks in advance,
Marcos
[post] : Decoding H264 VideoToolkit API fails with Error -8971 in VTDecompressionSessionCreate

Answer 1

You you MUST call CMVideoFormatDescriptionCreateFromH264ParameterSets first. The SPS/PPS may be stored/transmitted separately from the video stream. Or may come inline.
Note that for VTDecompressionSessionDecodeFrame your NALUs must be preceded with a size, and not a start code.
You can read more here:
Possible Locations for Sequence/Picture Parameter Set(s) for H.264 Stream