android-cloud-H5/static/screenAndroid/spsParser.js

//https://blog.csdn.net/lizhijian21/article/details/80982403
function ceil(val) {
  return Math.ceil(val);
}

//获取buf 的前n个bit组成的值
function u(bitCount, input) {
  let ret = 0;

  for (var i = 0; i < bitCount; i++) {
    ret <<= 1;


    if (input.data[Math.floor(input.index / 8)] & (0x80 >> (input.index % 8))) {
      ret += 1;
    }

    input.index++;
  }

  return ret;
}

/*无符号指数哥伦布编码(UE)
*哥伦布编码的码字code_word由三部分组成：code_word = [M个0] + [1] + [Info]
*其中，Info是一个携带信息的M位数据，每个哥伦布码的长度为（2M+1）位，每个码字都可由code_num产生。
*根据码字code_word解码出code_num值的过程如下：
*1. 首先读入M位以"1"为结尾的0；
*2. 根据得到的M，读入接下来的M位Info数据；
*3. 根据这个公式得到计算结果code_num = Info – 1 + 2M
*/

function ue(input, len) {
  let zeroNum = 0;
  while (input.index < len * 8) {
    if (input.data[Math.floor(input.index / 8)] & (0x80 >> (input.index % 8)))//遇到1则停止，统计0的个数
    {
      break;
    }

    zeroNum++;
    input.index++;
  }

  input.index++;

  let ret = 0;
  //计算
  for (var i = 0; i < zeroNum; i++) {
    ret <<= 1;
    if (input.data[Math.floor(input.index / 8)] & (0x80 >> input.index % 8)) {
      ret += 1;
    }

    input.index++;
  }

  return (1 << zeroNum) - 1 + ret;
}

//有符号哥伦布编码
function se(input, len) {
  let ueVal = ue(input, len);
  let k = ueVal;
  let nValue = ceil(k / 2);

  if (ueVal % 2 == 0)
    nValue = -nValue;
  return nValue;
}


function spsParser(buf) {
  let startBitIndex = 0;

  buf = buf.slice(4);//去除00 00 00 01竞争码
  let len = buf.length;

  //输入参数
  let input = {
    data: buf,
    index: startBitIndex
  };


  let forbidden_zero_bit = u(1, input);
  let nal_ref_idc = u(2, input);
  let nal_unit_type = u(5, input);
  let chroma_format_idc;

  if (nal_unit_type == 7) {
    let profile_idc = u(8, input);
    let constraint_set0_flag = u(1, input);
    let constraint_set1_flag = u(1, input);
    let constraint_set2_flag = u(1, input);
    let constraint_set3_flag = u(1, input);
    let constraint_set4_flag = u(1, input);
    let constraint_set5_flag = u(1, input);

    let reserved_zero_2bits = u(2, input);
    let level_idc = u(8, input);
    let seq_parameter_set_id = ue(input, len);

    if (profile_idc == 100 | profile_idc == 110 || profile_idc == 122 || profile_idc == 144) {
      chroma_format_idc = ue(input, len);

      if (chroma_format_idc == 3) {
        var residual_colour_transform_flag = u(1, input);
      }

      let bit_depth_luma_minus8 = ue(input, len);
      let bit_depth_chroma_minus8 = ue(input, len);
      let qpprime_y_zero_transform_bypass_flag = u(1, input);
      let seq_scaling_matrix_present_flag = u(1, input);

      let seq_scaling_list_present_flag = new Uint8Array(8);
      if (seq_scaling_matrix_present_flag) {
        for (var i = 0; i < 8; i++) {
          seq_scaling_list_present_flag[i] = u(1, input);
        }
      }
    }


    let log2_max_frame_num_minus4 = ue(input, len);
    let pic_order_cnt_type = ue(input, len);

    if (pic_order_cnt_type == 0)
      log2_max_pic_order_cnt_lsb_minus4 = ue(input, len);

    else if (pic_order_cnt_type == 1) {
      let delta_pic_order_always_zero_flag = u(1, input);
      let offset_for_non_ref_pic = se(input, len);
      let offset_for_top_to_bottom_field = se(input, len);
      let num_ref_frames_in_pic_order_cnt_cycle = ue(input, len);

      let offset_for_ref_frame = new Uint8Array[num_ref_frames_in_pic_order_cnt_cycle];

      for (var i = 0; i < num_ref_frames_in_pic_order_cnt_cycle; i++)
        offset_for_ref_frame[i] = se(input, len);
    }

    let num_ref_frames = ue(input, len);
    let gaps_in_frame_num_value_allowed_flag = u(1, input);
    let pic_width_in_mbs_minus1 = ue(input, len);
    let pic_height_in_map_units_minus1 = ue(input, len);

    let width = (pic_width_in_mbs_minus1 + 1) * 16;//可能还要进行裁剪处理
    let height = (pic_height_in_map_units_minus1 + 1) * 16;

    let frame_mbs_only_flag = u(1, input);

    if (!frame_mbs_only_flag) {
      u(1, input);
    }

    let direct_8x8_inference_flag = u(1, input);
    let frame_cropping_flag = u(1, input);

    if (frame_cropping_flag) {
      let frame_crop_left_offset = ue(input, len);
      let frame_crop_right_offset = ue(input, len);
      let frame_crop_top_offset = ue(input, len);
      let frame_crop_bottom_offset = ue(input, len);

      let crop_unit_x = 1;
      let crop_unit_y = 2 - frame_mbs_only_flag;

      if (chroma_format_idc == 1) {   //4:2:0
        crop_unit_x = 2;
        crop_unit_y = 2 * (2 - frame_mbs_only_flag);
      }
      else if (chroma_format_idc == 2) {    //4:2:2
        crop_unit_x = 2;
        crop_unit_y = 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);
    }

    return {
      width: width,
      height: height
    }

  }
}