通过解析sps中的哥伦布编码获取分辨率

bit_buffer是我自己写的一个数据缓存器，功能简单，看调用方法也能猜到干了什么，读者可以自行实现

 if len(frm.Sps) > 0 {
  bf := bit_buffer.NewBitBuffer()
  bf.FromBytes(frm.Sps[5:])
  profile_idc := bf.Read1Byte()
  bf.SkipNBits(8) // constraint_setx_flag + reserved
  level_idc := bf.Read1Byte()
  sps_id := bf.ReadUExpGolomb()
  if profile_idc == 100 || profile_idc == 110 ||
   profile_idc == 122 || profile_idc == 244 || profile_idc == 44 ||
   profile_idc == 83 || profile_idc == 86 || profile_idc == 118 ||
   profile_idc == 128 {
   chroma_format_idc := bf.ReadUExpGolomb()
   if chroma_format_idc == 3 {
    sparate_colour_plane_flag := bf.ReadNBits(1)
    _ = sparate_colour_plane_flag
   }
   bit_depth_luma_minus8 := bf.ReadUExpGolomb()
   bit_depth_chroma_minus8 := bf.ReadUExpGolomb()
   qpprime_y_zoro_transform_bypass_flag := bf.ReadNBits(1)
   seq_scalling_matrix_present_flag := bf.ReadNBits(1)
   if seq_scalling_matrix_present_flag != 0 {
    forlimit := 0
    if chroma_format_idc != 3 {
     forlimit = 8
    } else {
     forlimit = 12
    }
    for i := 0; i < forlimit; i++ {
     seq_scaling_list_present_flag := bf.ReadNBits(1)
     _ = seq_scaling_list_present_flag
    }
   }
   _ = bit_depth_luma_minus8
   _ = bit_depth_chroma_minus8
   _ = qpprime_y_zoro_transform_bypass_flag
   _ = seq_scalling_matrix_present_flag
  }
  log2_max_frame_num_minus4 := bf.ReadUExpGolomb()
  pic_order_cnt_type := bf.ReadUExpGolomb()
  if pic_order_cnt_type == 0 {
   log2_max_pic_order_cnt_lsb_minus4 := bf.ReadUExpGolomb()
   _ = log2_max_pic_order_cnt_lsb_minus4
  } else if pic_order_cnt_type == 1 {
   delta_pic_order_always_zero_flag := bf.ReadNBits(1)
   offset_for_non_ref_pic := bf.ReadSExpGolomb()
   offset_for_top_to_bottom_field := bf.ReadSExpGolomb()
   num_ref_frames_in_pic_order_cnt_cycle := bf.ReadUExpGolomb()
   for i := 0; i < num_ref_frames_in_pic_order_cnt_cycle; i++ {
    offset_for_ref_frame := bf.ReadSExpGolomb()
    _ = offset_for_ref_frame
   }
   _ = delta_pic_order_always_zero_flag
   _ = offset_for_non_ref_pic
   _ = offset_for_top_to_bottom_field
  }
  max_num_ref_frames := bf.ReadUExpGolomb()
  gaps_in_frame_num_value_allowed_flag := bf.ReadNBits(1)
  pic_width_in_mbs_minus1 := bf.ReadUExpGolomb()
  pic_height_in_map_units_minus1 := bf.ReadUExpGolomb()
  frame_mbs_only_flag := bf.ReadNBits(1)
  if frame_mbs_only_flag == 0 {
   mb_adaptive_frame_field_flag := bf.ReadNBits(1)
   _ = mb_adaptive_frame_field_flag
  }
  direct_8x8_inference_flag := bf.ReadNBits(1)
  frame_cropping_flag := bf.ReadNBits(1)
  if frame_cropping_flag != 0 {
   frame_crop_left_offset := bf.ReadUExpGolomb()
   frame_crop_right_offset := bf.ReadUExpGolomb()
   frame_crop_top_offset := bf.ReadUExpGolomb()
   frame_crop_bottom_offset := bf.ReadUExpGolomb()

   // 计算分辨率
   width = (pic_width_in_mbs_minus1 + 1) * 16
   height = (2 - frame_mbs_only_flag) * (pic_height_in_map_units_minus1 + 1) * 16
   crop_unit_x := 2
   crop_unit_y := 2 * (2 - frame_mbs_only_flag)
   width -= crop_unit_x * (frame_crop_left_offset + frame_crop_right_offset)
   height -= crop_unit_y * (frame_crop_top_offset + frame_crop_bottom_offset)
  } else {
   // 计算分辨率
   width = (pic_width_in_mbs_minus1 + 1) * 16
   height = (2 - frame_mbs_only_flag) * (pic_height_in_map_units_minus1 + 1) * 16
  }
  _ = max_num_ref_frames
  _ = gaps_in_frame_num_value_allowed_flag
  _ = frame_mbs_only_flag
  _ = direct_8x8_inference_flag
  _ = log2_max_frame_num_minus4
  _ = level_idc
  _ = sps_id
  frm.Width = uint(width)
  frm.Height = uint(height)
 }