Module h264 

H264 SDP and payload-format helpers derived from RFC 6184.

Packet helpers in this module receive the H264 RTP payload slice. The first byte of that slice identifies the packetization mode used by the packet. Decoder-refresh detection needs to recognize IDR access units in all packet shapes that browsers commonly send.

Single NAL unit packet

+-------------+----------------------+
| NAL header  | NAL payload          |
+-------------+----------------------+
| F NRI Type  | ...                  |
+-------------+----------------------+

STAP-A aggregation packet

+---------------+----------+-------------+----------+-------------+
| STAP-A header | NAL size | NAL bytes   | NAL size | NAL bytes   |
+---------------+----------+-------------+----------+-------------+
| Type=24       | 16 bits  | starts with | 16 bits  | starts with |
|               |          | NAL header  |          | NAL header  |
+---------------+----------+-------------+----------+-------------+

FU-A fragmentation packet

+---------------+-------------+----------------------+
| FU indicator  | FU header   | fragment payload     |
+---------------+-------------+----------------------+
| Type=28       | S E R Type  | first fragment if S=1 |
+---------------+-------------+----------------------+

rfc 6184 maps profile-level-id to three bytes:

profile_idc | profile-iop | level_idc

profile-iop bit layout:
 7   6   5   4   3   2   1   0
+---+---+---+---+---+---+---+---+
|c0 |c1 |c2 |c3 |c4 |c5 | r | r |
+---+---+---+---+---+---+---+---+

cN = constraint_setN_flag
r  = reserved_zero bit

Structs

ProfileIopPattern 🔒

masked profile-iop matcher for profile-equivalence wildcard bits

ProfileLevelId

parsed H264 profile-level-id capability

ProfilePattern 🔒

one accepted RFC 6184 profile-equivalence row

Enums

LevelIdc

H264 decoder capability level

PacketizationMode

H264 RTP packetization mode.

Profile

H264 sub-profile after equivalent RFC 6184 encodings are normalized

Constants

BASELINE_IDC 🔒

CAVLC_444_IDC 🔒

EXTENDED_IDC 🔒

FU_END_BIT

FU-A end bit in the FU header.

FU_START_BIT

FU-A start bit in the FU header.

HIGH_10_IDC 🔒

HIGH_422_IDC 🔒

HIGH_444_IDC 🔒

HIGH_IDC 🔒

IOP_CONSTRAINED_BASELINE 🔒

IOP_CONSTRAINT_SET0 🔒

IOP_CONSTRAINT_SET1 🔒

IOP_CONSTRAINT_SET2 🔒

IOP_CONSTRAINT_SET3 🔒

IOP_NONE 🔒

IOP_PROFILE_PATTERN_LOW_ZERO_MASK 🔒

LEVEL_1B_IDCS 🔒

LEVEL_1B_OTHER_IDC 🔒

LEVEL_1_1_IDC 🔒

MAIN_IDC 🔒

NAL_REF_IDC_HIGH

Highest NRI value for reference NAL units.

NAL_UNIT_TYPE_FU_A

H264 FU-A fragmentation packet type.

NAL_UNIT_TYPE_IDR

H264 IDR slice NAL unit type.

NAL_UNIT_TYPE_MASK

Mask for the H264 NAL unit type field.

NAL_UNIT_TYPE_STAP_A

H264 STAP-A aggregation packet type.

PROFILE_PATTERNS 🔒

Functions

decode_hex_byte 🔒

decode_hex_nibble 🔒

fu_a_starts_idr 🔒

Detects whether a FU-A packet is the first fragment of an IDR NAL unit.

level_1b_profile_level_id_bytes 🔒

level_idc_value 🔒

normalized_level_idc 🔒

pack_profile_level_id 🔒

parse_profile_level_id_bytes 🔒

payload_starts_idr

Detects an H264 RTP packet that starts an IDR access unit.

profile_bytes 🔒

profile_from_bytes 🔒

profile_level_id_bytes 🔒

stap_a_contains_idr 🔒

Scans a STAP-A payload for any contained IDR NAL unit.