roboto.experimental.video.h264#

Minimal H.264 Annex B bitstream inspection.

Implements only the byte-level parsing needed to drive a GOP-aware decoder: splitting a frame’s data into NAL units and detecting keyframes (IDR slices). It neither decodes video nor parses variable-length (Exp-Golomb) fields — the decoder reads everything else (dimensions, reference frame count, …) from the in-band parameter sets.

Module Contents#

class roboto.experimental.video.h264.NalUnit#

One NAL unit split out of an Annex B-framed H.264 frame.

data: bytes#

header byte included, start code excluded.

Type:

The unit’s bytes

type: int#

nal_unit_type from the unit’s header byte.

class roboto.experimental.video.h264.NalUnitType#

Bases: enum.IntEnum

H.264 NAL unit types (ITU-T H.264 table 7-1) relevant to this module.

NAL headers can carry any 5-bit type value, so NalUnit.type is a plain int; compare against these members for the types that matter here.

IDR_SLICE = 5#
NON_IDR_SLICE = 1#
PICTURE_PARAMETER_SET = 8#
SEI = 6#
SEQUENCE_PARAMETER_SET = 7#
roboto.experimental.video.h264.find_nal_units(data)#

Split Annex B-framed H.264 data into its NAL units.

Parameters:

data (bytes) – One frame’s Annex B-framed bytes, using 3-byte or 4-byte start codes.

Returns:

The frame’s NAL units in bitstream order. Each unit’s data is a copy of the unit’s bytes (header included, start code excluded).

Return type:

list[NalUnit]

Examples

>>> from roboto.experimental.video import NalUnitType, find_nal_units
>>> units = find_nal_units(annex_b_frame_bytes)  
>>> [unit.type for unit in units]  
[7, 8, 5]
roboto.experimental.video.h264.is_keyframe(data)#

Whether the Annex B-framed H.264 frame contains an IDR slice.

An IDR slice is a clean decoder entry point: decoding may start at this frame without any earlier GOP state. Frames without one are delta frames, decodable only after the preceding keyframe has been fed to the decoder.

Parameters:

data (bytes) – One frame’s Annex B-framed bytes.

Returns:

True when the frame contains an IDR slice.

Return type:

bool

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