#!/usr/bin/env python3 """ Generates an AV1 bitstream with two temporal units whose sequence headers share identical {profile, max_frame_size, bitdepth, chroma sampling, color config} but differ in non-dimensional flags (use_128x128_superblock, enable_cdef, enable_restoration, film_grain_params_present). When fed through media::AV1Decoder, TU1 must yield kConfigChange (first sequence header). TU2 must NOT yield kConfigChange (the gate at av1_decoder.cc:367-383 only checks size/profile/bitdepth/colorspace), yet SubmitDecode() will be invoked with the *new* sequence header carrying the flipped flags. Each TU is a lossless 256x256 4:2:0 8-bit shown key frame so that libgav1's OBU parser short-circuits loop-filter / CDEF / LR / tx-mode parsing regardless of the seq-header enable_* flags. Tile data is a single dummy byte; libgav1's ObuParser only records tile buffer offsets without entropy-decoding them. """ import struct import sys class BitWriter: def __init__(self): self.bits = [] def f(self, value, n): for i in range(n - 1, -1, -1): self.bits.append((value >> i) & 1) def b(self, value): self.f(1 if value else 0, 1) def trailing_bits(self): self.bits.append(1) while len(self.bits) % 8: self.bits.append(0) def align_zero(self): while len(self.bits) % 8: self.bits.append(0) def bytes(self): assert len(self.bits) % 8 == 0 out = bytearray() for i in range(0, len(self.bits), 8): byte = 0 for j in range(8): byte = (byte << 1) | self.bits[i + j] out.append(byte) return bytes(out) def leb128(v): out = bytearray() while True: b = v & 0x7F v >>= 7 if v: out.append(b | 0x80) else: out.append(b) return bytes(out) def obu(obu_type, payload): # forbidden=0, type(4), extension=0, has_size=1, reserved=0 header = bytes([(obu_type << 3) | 0x02]) return header + leb128(len(payload)) + payload def sequence_header_obu(use_128x128_superblock, enable_cdef, enable_restoration, film_grain_params_present): w = BitWriter() w.f(0, 3) # seq_profile = Main w.b(False) # still_picture w.b(False) # reduced_still_picture_header w.b(False) # timing_info_present_flag # decoder_model_info_present_flag: only when timing_info_present_flag. w.b(False) # initial_display_delay_present_flag w.f(0, 5) # operating_points_cnt_minus_1 w.f(0, 12) # operating_point_idc[0] w.f(0, 5) # seq_level_idx[0] (level 2.0, major<=3 -> no tier bit) # frame_width_bits_minus_1 / frame_height_bits_minus_1 w.f(7, 4) # 8 bits w.f(7, 4) # 8 bits w.f(255, 8) # max_frame_width_minus_1 -> 256 w.f(255, 8) # max_frame_height_minus_1 -> 256 w.b(False) # frame_id_numbers_present_flag w.b(use_128x128_superblock) w.b(False) # enable_filter_intra w.b(False) # enable_intra_edge_filter w.b(False) # enable_interintra_compound w.b(False) # enable_masked_compound w.b(False) # enable_warped_motion w.b(False) # enable_dual_filter w.b(False) # enable_order_hint # (no enable_jnt_comp / enable_ref_frame_mvs) w.b(False) # seq_choose_screen_content_tools w.b(False) # seq_force_screen_content_tools = 0 # force_screen_content_tools == 0 -> no integer_mv read # (no order_hint_bits_minus_1) w.b(False) # enable_superres w.b(enable_cdef) w.b(enable_restoration) # color_config (profile 0, 8-bit 4:2:0) w.b(False) # high_bitdepth w.b(False) # mono_chrome w.b(False) # color_description_present_flag w.b(False) # color_range w.f(0, 2) # chroma_sample_position w.b(False) # separate_uv_delta_q w.b(film_grain_params_present) w.trailing_bits() return obu(1, w.bytes()) # OBU_SEQUENCE_HEADER def frame_obu(film_grain_params_present): w = BitWriter() # uncompressed_header() w.b(False) # show_existing_frame w.f(0, 2) # frame_type = KEY_FRAME w.b(True) # show_frame # error_resilient_mode inferred = 1 for KEY+show_frame w.b(True) # disable_cdf_update (so no disable_frame_end_update_cdf) # allow_screen_content_tools inferred = 0 (seq_force_screen_content_tools=0) # frame_id_numbers_present = 0 -> no current_frame_id w.b(False) # frame_size_override_flag # order_hint_bits = 0 -> no order_hint # primary_ref_frame inferred = NONE (intra) # decoder_model_info_present_flag = 0 -> no buffer_removal_time # refresh_frame_flags inferred = 0xff (KEY+show_frame) # IntraFrame && refresh==0xff -> no ref_order_hint loop # frame_size(): override=0 -> use max; superres disabled -> no bits w.b(False) # render_and_frame_size_different # allow_screen_content_tools=0 -> no allow_intrabc # disable_cdf_update=1 -> no disable_frame_end_update_cdf bit # tile_info() w.b(True) # uniform_tile_spacing_flag w.b(False) # increment_tile_cols_log2 (stop) w.b(False) # increment_tile_rows_log2 (stop) # tile_bits = 0 -> no context_update_id / tile_size_bytes # quantization_params() w.f(0, 8) # base_q_idx = 0 (CodedLossless) w.b(False) # DeltaQYDc.delta_coded # separate_uv_delta_q = 0 -> no diff_uv_delta bit w.b(False) # DeltaQUDc.delta_coded w.b(False) # DeltaQUAc.delta_coded w.b(False) # using_qmatrix # segmentation_params() w.b(False) # segmentation_enabled # delta_q_params(): base_q_idx==0 -> no bits # delta_lf_params(): delta_q_present==0 -> no bits # loop_filter / cdef / lr / tx_mode: skipped (CodedLossless / AllLossless) # frame_reference_mode(): intra -> no bits # skip_mode_params(): not allowed -> no bits # allow_warped_motion: intra -> no bits w.b(False) # reduced_tx_set # global_motion_params(): intra -> no bits if film_grain_params_present: w.b(False) # apply_grain = 0 w.align_zero() # byte_alignment() inside Frame OBU fh = w.bytes() tile_data = b'\x00' # 1-byte dummy tile (parser only records offset/size) return obu(6, fh + tile_data) # OBU_FRAME def temporal_unit(sb128, cdef, lr, fg): td = obu(2, b'') # OBU_TEMPORAL_DELIMITER return td + sequence_header_obu(sb128, cdef, lr, fg) + frame_obu(fg) def ivf_header(num_frames, w=256, h=256): return (b'DKIF' + struct.pack('