Detect MPEG4/H264 I-Frame (IDR) in RTP stream

Question

I need to detect MPEG4 I-Frame in RTP packet. I know how to remove RTP header and get the MPEG4 frame in it, but I can\'t figure out how to identify the I-Frame.

Doe

Answer 1

For H264:

1. Remove RTP header.
2. If chunk NAL type (in first byte) is SPS (7) or PPS (8) mark the frame as IFrame (many cameras not use SPS and PPS (Axis included)).
3. If chunk NAL type is #28 FU A (fragmentation unit A), check FU Header (next byte) if is NAL type IDR (5) (IDR (Instantaneous Decoding Refresh) Picture) is an IFrame.

Examples:

nal_ref_idc: 3, nal type: 7 (0x07) descripcion: 7 (SPS)

00000000  24 00 00 2B 80 60 22 ED 96 57 3E 68 57 F3 22 B5  $..+.`"í.W>hWó"µ

00000010  67 64 00 1E AD 84 01 0C 20 08 61 00 43 08 02 18  gd..­... .a.C...

00000020  40 10 C2 00 84 2B 50 5A 09 34 DC 04 04 04 08  @.Â..+PZ.4Ü....

nal_ref_idc: 3, nal type: 8 (0x08) descripcion: 8 (PPS)

00000000  24 00 00 10 80 60 22 EE 96 57 3E 68 57 F3 22 B5  $....`"î.W>hWó"µ
00000010  68 EE 3C B0  hî<°

FU_A (fragmentation unit A) 
nal_ref_idc: 3, nal type: 5 (0x05) descripcion: 5 (IDR (Instantaneous Decoding Refresh) Picture)
00000000  24 00 05 96 80 60 22 F1 96 57 3E 68 57 F3 22 B5  $....`"ñ.W>hWó"µ
00000010  7C 05 A0 AA 2F 81 92 AB CA FE 9E 34 D8 06 AD 74  |. ª/..«Êþ.4Ø.­t
...