Decoding H264 VideoToolkit API fails with Error -8971 in VTDecompressionSessionCreate - ios

Question

I am trying to write a Video decoder using the Hardware supported Video Toolkit Decoder. But if I try to initialize the decoding session like in the example posted below, I get the error -8971 while calling VTDecompressionSessionCreate. Can anyone tell me what I am doing wrong here?
Thank you and best regards,
Oliver
OSStatus status;
int tmpWidth = sps.EncodedWidth();
int tmpHeight = sps.EncodedHeight();
NSLog(#"Got new Width and Height from SPS - %dx%d", tmpWidth, tmpHeight);
const VTDecompressionOutputCallbackRecord callback = { ReceivedDecompressedFrame, self };
status = CMVideoFormatDescriptionCreate(NULL,
kCMVideoCodecType_H264,
tmpWidth,
tmpHeight,
NULL,
&decoderFormatDescription);
if (status == noErr)
{
// Set the pixel attributes for the destination buffer
CFMutableDictionaryRef destinationPixelBufferAttributes = CFDictionaryCreateMutable(
NULL, // CFAllocatorRef allocator
0, // CFIndex capacity
&kCFTypeDictionaryKeyCallBacks,
&kCFTypeDictionaryValueCallBacks);
SInt32 destinationPixelType = kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange;
CFDictionarySetValue(destinationPixelBufferAttributes,kCVPixelBufferPixelFormatTypeKey, CFNumberCreate(NULL, kCFNumberSInt32Type, &destinationPixelType));
CFDictionarySetValue(destinationPixelBufferAttributes,kCVPixelBufferWidthKey, CFNumberCreate(NULL, kCFNumberSInt32Type, &tmpWidth));
CFDictionarySetValue(destinationPixelBufferAttributes, kCVPixelBufferHeightKey, CFNumberCreate(NULL, kCFNumberSInt32Type, &tmpHeight));
CFDictionarySetValue(destinationPixelBufferAttributes, kCVPixelBufferOpenGLCompatibilityKey, kCFBooleanTrue);
// Set the Decoder Parameters
CFMutableDictionaryRef decoderParameters = CFDictionaryCreateMutable(
NULL, // CFAllocatorRef allocator
0, // CFIndex capacity
&kCFTypeDictionaryKeyCallBacks,
&kCFTypeDictionaryValueCallBacks);
CFDictionarySetValue(decoderParameters,kVTDecompressionPropertyKey_RealTime, kCFBooleanTrue);
// Create the decompression session
// Throws Error -8971 (codecExtensionNotFoundErr)
status = VTDecompressionSessionCreate(NULL, decoderFormatDescription, decoderParameters, destinationPixelBufferAttributes, &callback, &decoderDecompressionSession);
// release the dictionaries
CFRelease(destinationPixelBufferAttributes);
CFRelease(decoderParameters);
// Check the Status
if(status != noErr)
{
NSLog(#"Error %d while creating Video Decompression Session.", (int)status);
continue;
}
}
else
{
NSLog(#"Error %d while creating Video Format Descripttion.", (int)status);
continue;
}

Answer 1

I also stumbled with kVTVideoDecoderBadDataErr. In my case I was changing the header 0x00000001 with the size of the NAL package which included the 4 bytes of this header, that was the reason. I changed the size to not include these 4 bytes (frame_size = sizeof(NAL) - 4). This size should be encoded in big-endian.

Answer 2

You need to create the CMFormatDescriptionRef from your SPS and PPS like
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);
Also if you are getting your Video Data in Annex-B format you need to remove the start code and replace it with the 4-Byte size information for the decoder to recognize it as avcc formated (Thats what the 5th parameter to CMVideoFormatDescriptionCreateFromH264ParameterSets is for).

Answer 3

#Joride
refer to http://www.szatmary.org/blog/25
It explains that the header (first) byte of each buffer within a NALU describes the buffer's type. You need to mask off these bits and compare them to the table provided. Note the comment about the bit fields. You need to mask the byte with 0x1f to the type value.