sequence parameter set

[terryleung]

Hi all,

I am writing a program to extract the sequence_parameter_set_rbsp() from a mp4 file
However, i got into troubles

The mp4dump of the file(avcC box only)

type avcC
configurationVersion = 1 (0x01)
AVCProfileIndication = 66 (0x42)
profile_compatibility = 192 (0xc0)
AVCLevelIndication = 13 (0x0d)
reserved = 63 (0x3f) <6 bits>
lengthSizeMinusOne = 3 (0x3) <2 bits>
reserved1 = 7 (0x7) <3 bits>
numOfSequenceParameterSets = 1 (0x01) <5 bits>
sequenceParameterSetLength = 23 (0x0017)
sequenceParameterSetNALUnit = <23 bytes>
67 42 c0 0d 9a 74 0a 0f d8 08 80 00 00 03 00 80
00 00 0f 47 8a 15 50
numOfPictureParameterSets = 1 (0x01)
pictureParameterSetLength = 4 (0x0004)
pictureParameterSetNALUnit = <4 bytes> 68 ce 3c 80


I try to decode the sequenceParameterSetNALUnit
From my understanding

The first byte 67 is nal unit type where the last 5 bit indicate it is a sequence parameter set
and Then I decode from the second byte as a seq_parameter_set_rbsp() (in ISO/IEC 14496-10:2004 page 31)

After I decoded it, there are a lot of bit that is not used a the bitstream decoding process

I have tried to use x264 to encode a seq parameter set by using the function x264_nal_encode
Then I use my decode function to decode it, and it work very well (without any unused bit)

where is the seq_parameter_set_rbsp located in sequenceParameterSetNALUnit ???

[Guest]

What do you mean by unused bits? Give the details of the parsing.

[Trahald]

67 42 c0 0d 9a 74 0a 0f d8 08 80 00 00 03 00 80
00 00 0f 47 8a 15 50
42 == profile_idc 66
c0 == constrained_set0_flag0 and 1 == 1 and 2 and 3 == 0
0d == level 1.3
9a == ( binary 10011010 ) left to right
---> the first '1' exp-golomb xlates to a 0 (seq_parameter_set_id )
---> the 2nd-6th bits '00110' is a 5 (log2_max_frame_num_minus4)
---> the 7th bit '1' is 0 (pic_order_cnt_type )

id continue but im doing it by hand and may make an error

just watch the 00 00 03 in hex you pasted as the 03 is dropped

[terryleung]

thanks, after i drop the 03, the things work great!