[Live-devel] Frames are corrupted

[Ross Finlayson]

On May 1, 2014, at 9:58 AM, Vikram Singh <vikram at vizexperts.com> wrote:

> Hi ross,
> I am not able to get SPS and PPS units from the encoder.
> I am using CUDA Video Encode library which has a function NVGetSPSPPS().
[...]
>>  
>> Sorry I am not getting the detailed documentation for the function NVGetSPSPPS(). Please help me.

"NVGetSPSPPS()" is not a function in our code, so I don't know why you're asking here.  Why don't you ask whoever provided you the "CUDA Video Encode library"?


However...

> NVGetSPSPPS() returns  a buffer to SPS and PPS.
> The problem is that I don’t have the formatting for this buffer so that I could separate SPS and PPS units from each other.
>  
> In my case this buffer is
>  
>                00 24 67 4d 40 1e f6 04 00 83 7f e0 00 80 00 62 00 00 07 d2 00 01 d4 c1 c0 00 00 27 a1 20 00 02 62 5a 17 79 70 50 00 04 68 ee 3c 80

It seems quite clear that the encoding is:
	Sequence of:
		2-byte 'length' (in big-endian order)
		'length' bytes, containing the NAL unit (without a preceding 'start code')


>  According to my assumption 
>  
>                    00 00 00 01 67 4d 40 1e f6 04 00 83 7f e0 00 80 00 62 00 00 07 d2 00 01 d4 c1 c0 00 00 27 a1 20 00 02 62 5a 17 79 70 50 00 04 ==> sps
> And            00 00 00 01 68 ee 3c 80 ==> pps

Not quite, because it seems clear that the "00 24" is a length field (i.e., 0x0024 == 36 decimal).  Therefore SPS is
	67 4d 40 1e f6 04 00 83 7f e0 00 80 00 62 00 00 07 d2 00 01 d4 c1 c0 00 00 27 a1 20 00 02 62 5a 17 79 70 50
then the next two bytes - 00 04 - are also a length field (therefore, *not* part of the NAL unti), so PPS is
	68 ee 3c 80

You should therefore pass these two NAL units - without start codes - as parameters to
	H264VideoRTPSink::createNew()
This will be the second form of "H264VideoRTPSink::createNew()" - i.e., the form that has the signature
	static H264VideoRTPSink* createNew(UsageEnvironment& env, Groupsock* RTPgs, unsigned char rtpPayloadFormat,
					u_int8_t const* sps, unsigned spsSize,
					u_int8_t const* pps, unsigned ppsSize,
					unsigned profile_level_id);

Note that you also need to pass a "profile_level_id" parameter.  This is actually a flaw in the code, because you can generate this parameter from the 2nd through 4th bytes of the SPS NAL unit.  (I.e., this parameter shouldn't be needed.)  So, in your case, the "profile_level_id" parameter would be
	0x4d401e


Ross Finlayson
Live Networks, Inc.
http://www.live555.com/

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