从RTSP的DESCRIBE返回的SDP中计算视频宽和高

以下限于H264.

• SDP中计算宽高用到的参数

  
  
  

  DESCRIBE成功后返回sdp信息中的SPS信息局部

• 计算公式

// 计算宽和高 简易公式
Width  = (pic_width_in_mbs_minus1        + 1) * 16;
Height = (pic_height_in_map_units_minus1 + 1) * 16;
Width  -= (frame_crop_left_offset + frame_crop_right_offset) * 2;
Height -= (frame_crop_top_offset  + frame_crop_bottom_offset) * 2;

更详细复杂的可参见: http://ju.outofmemory.cn/entry/208773

• 计算实例

Width  = (119 + 1) * 16 - (0 + 0) * 2 = 1920
Height = (67  + 1) * 16 - (0 + 4) * 2 = 1088 - 8 = 1080

• 代码实例

        Width  = (pic_width_in_mbs_minus1        + 1) * 16;
        Height = (pic_height_in_map_units_minus1 + 1) * 16;

        int frame_mbs_only_flag;
        int frame_cropping_flag, frame_crop_left_offset, frame_crop_right_offset;
        int frame_crop_top_offset, frame_crop_bottom_offset;

        ...

        frame_cropping_flag = u(1,buf,StartBit);
        if (frame_cropping_flag)
        {
            frame_crop_left_offset   = ...;
            frame_crop_right_offset  = ...;
            frame_crop_top_offset    = ...;
            frame_crop_bottom_offset = ...;

            Width  -= (frame_crop_left_offset + frame_crop_right_offset) << 0x1;
            Height -= (frame_crop_top_offset  + frame_crop_bottom_offset) << 0x1;
        }

References:
http://ju.outofmemory.cn/entry/208773
http://www.latelee.org/my-study/get-width-height-framerate-from-bitstream.html