parseSPS()

H264Info fl::H264::parseSPS ( fl::span< const fl::u8 > spsData, fl::string * error_message = nullptr )

static

Definition at line 85 of file h264.cpp.hpp.

                                                                           {
    H264Info info;
 
    if (spsData.size() < 4) {
        if (error_message) *error_message = "SPS data too small";
        return info;
    }
 
    BitReader br(spsData);
 
    // NAL unit header: forbidden_zero_bit(1) + nal_ref_idc(2) + nal_unit_type(5)
    fl::u8 nalHeader = (fl::u8)br.readBits(8);
    fl::u8 nalType = nalHeader & 0x1F;
    FL_UNUSED(nalType); // should be 7 for SPS
 
    // SPS header
    fl::u8 profile_idc = (fl::u8)br.readBits(8);
    br.readBits(8); // constraint_set flags + reserved
    fl::u8 level_idc = (fl::u8)br.readBits(8);
    br.readUE(); // seq_parameter_set_id
 
    info.profile = profile_idc;
    info.level = level_idc;
 
    // High profile extensions
    fl::u32 chromaFormatIdc = 1; // default
    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 ||
        profile_idc == 138 || profile_idc == 139 || profile_idc == 134 ||
        profile_idc == 135) {
        chromaFormatIdc = br.readUE();
        if (chromaFormatIdc == 3) {
            br.readBits(1); // separate_colour_plane_flag
        }
        br.readUE(); // bit_depth_luma_minus8
        br.readUE(); // bit_depth_chroma_minus8
        br.readBits(1); // qpprime_y_zero_transform_bypass_flag
 
        fl::u32 seqScalingMatrixPresent = br.readBits(1);
        if (seqScalingMatrixPresent) {
            int limit = (chromaFormatIdc != 3) ? 8 : 12;
            for (int i = 0; i < limit; i++) {
                if (br.readBits(1)) { // seq_scaling_list_present_flag
                    skipScalingList(br, (i < 6) ? 16 : 64);
                }
            }
        }
    }
 
    br.readUE(); // log2_max_frame_num_minus4
    fl::u32 picOrderCntType = br.readUE();
    if (picOrderCntType == 0) {
        br.readUE(); // log2_max_pic_order_cnt_lsb_minus4
    } else if (picOrderCntType == 1) {
        br.readBits(1); // delta_pic_order_always_zero_flag
        br.readSE(); // offset_for_non_ref_pic
        br.readSE(); // offset_for_top_to_bottom_field
        fl::u32 numRefFramesInPoc = br.readUE();
        for (fl::u32 i = 0; i < numRefFramesInPoc; i++) {
            br.readSE(); // offset_for_ref_frame
        }
    }
 
    info.numRefFrames = (fl::u8)br.readUE(); // max_num_ref_frames
    br.readBits(1); // gaps_in_frame_num_value_allowed_flag
 
    fl::u32 picWidthInMbs = br.readUE() + 1;
    fl::u32 picHeightInMapUnits = br.readUE() + 1;
 
    fl::u32 frameMbsOnly = br.readBits(1);
    if (!frameMbsOnly) {
        br.readBits(1); // mb_adaptive_frame_field_flag
    }
 
    br.readBits(1); // direct_8x8_inference_flag
 
    // Frame cropping
    fl::u32 cropLeft = 0, cropRight = 0, cropTop = 0, cropBottom = 0;
    fl::u32 frameCropping = br.readBits(1);
    if (frameCropping) {
        cropLeft = br.readUE();
        cropRight = br.readUE();
        cropTop = br.readUE();
        cropBottom = br.readUE();
    }
 
    // Calculate dimensions
    fl::u32 width = picWidthInMbs * 16;
    fl::u32 height = (2 - frameMbsOnly) * picHeightInMapUnits * 16;
 
    // Apply cropping
    fl::u32 cropUnitX = 1, cropUnitY = 2 - frameMbsOnly;
    if (chromaFormatIdc == 1) {
        cropUnitX = 2;
        cropUnitY *= 2;
    } else if (chromaFormatIdc == 2) {
        cropUnitX = 2;
        cropUnitY *= 1;
    }
 
    width -= (cropLeft + cropRight) * cropUnitX;
    height -= (cropTop + cropBottom) * cropUnitY;
 
    info.width = (fl::u16)width;
    info.height = (fl::u16)height;
    info.isValid = true;
 
    return info;
}

References FL_UNUSED, fl::H264Info::height, fl::height, fl::H264Info::isValid, fl::H264Info::level, fl::H264Info::numRefFrames, fl::H264Info::profile, fl::span< T, Extent >::size(), fl::H264Info::width, and fl::width.

Referenced by parseH264Info().

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