H264 从序列参数集 (SPS) NAL 单元获取帧高度和宽度

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问题描述

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大家好，我一直在试图找出如何从 SPS 最终单位计算宽度和高度.我有具有这些参数的 H264 视频

Hello guys I've been trying to find out how to calculate width a height from SPS nal unit. I have H264 video which has these parameters

h264 (High), yuvj420p(pc), 1280x720 [SAR 1:1 DAR 16:9], 20 fps, 20 tbr, 1200k tbn, 40 tbc

我一直在寻找可以计算宽度 (1280) 和高度 (720) 的公式，但没有找到任何可以帮助我的公式.现在我正在使用 这个公式，它适用于大多数 H264流，但在这种情况下高度和宽度是 80x48

I've been searching for a formula which would calculate width (1280) and height (720) but have't found any which would help me. Right now I'm using this formula and it works for most H264 streams but in this case height and width is 80x48

if(frame_cropping_flag) {
    width = ((pic_width_in_mbs_minus1 +1)*16) - frame_crop_left_offset*2 - frame_crop_right_offset*2;
    height= ((2 - frame_mbs_only_flag)* (pic_height_in_map_units_minus1 +1) * 16) - (frame_crop_top_offset * 2) - (frame_crop_bottom_offset * 2);
}
else {
    width = ((pic_width_in_mbs_minus1 +1)*16);
    height= ((2 - frame_mbs_only_flag)* (pic_height_in_map_units_minus1 +1) * 16);
}

这里是 base64 格式的 SPS

here is SPS as base64

Z2QAKa2EBUViuKxUdCAqKxXFYqOhAVFYrisVHQgKisVxWKjoQFRWK4rFR0ICorFcVio6ECSFITk8nyfk/k/J8nm5s00IEkKQnJ5Pk/J/J+T5PNzZprQCgC3YCqQAAAMB4AAASwGBAAH0AAADAjKAve+F4RCNQA==

这是我解析的 SPS:

here is SPS that I've parsed:

======= SPS =======
 profile_idc : 100
 constraint_set0_flag : 0
 constraint_set1_flag : 0
 constraint_set2_flag : 0
 constraint_set3_flag : 0
 constraint_set4_flag : 0
 constraint_set5_flag : 0
 reserved_zero_2bits : 0
 level_idc : 41
 seq_parameter_set_id : 0
 chroma_format_idc : 1
 separate_colour_plane_flag : 0
 bit_depth_luma_minus8 : 0
 bit_depth_chroma_minus8 : 0
 qpprime_y_zero_transform_bypass_flag : 0
 seq_scaling_matrix_present_flag : 1
 log2_max_frame_num_minus4 : 41
 pic_order_cnt_type : 4
   log2_max_pic_order_cnt_lsb_minus4 : 0
   delta_pic_order_always_zero_flag : 0
   offset_for_non_ref_pic : 0
   offset_for_top_to_bottom_field : 0
   num_ref_frames_in_pic_order_cnt_cycle : 0
 num_ref_frames : 2
 gaps_in_frame_num_value_allowed_flag : 0
 pic_width_in_mbs_minus1 : 4
 pic_height_in_map_units_minus1 : 2
 frame_mbs_only_flag : 1
 mb_adaptive_frame_field_flag : 0
 direct_8x8_inference_flag : 0
 frame_cropping_flag : 0
   frame_crop_left_offset : 0
   frame_crop_right_offset : 0
   frame_crop_top_offset : 0
   frame_crop_bottom_offset : 0
 vui_parameters_present_flag : 0
=== VUI ===
 aspect_ratio_info_present_flag : 0
   aspect_ratio_idc : 0
     sar_width : 0
     sar_height : 0
 overscan_info_present_flag : 0
   overscan_appropriate_flag : 0
 video_signal_type_present_flag : 0
   video_format : 0
   video_full_range_flag : 0
   colour_description_present_flag : 0
     colour_primaries : 0
   transfer_characteristics : 0
   matrix_coefficients : 0
 chroma_loc_info_present_flag : 0
   chroma_sample_loc_type_top_field : 0
   chroma_sample_loc_type_bottom_field : 0
 timing_info_present_flag : 0
   num_units_in_tick : 0
   time_scale : 0
   fixed_frame_rate_flag : 0
 nal_hrd_parameters_present_flag : 0
 vcl_hrd_parameters_present_flag : 0
   low_delay_hrd_flag : 0
 pic_struct_present_flag : 0
 bitstream_restriction_flag : 0
   motion_vectors_over_pic_boundaries_flag : 0
   max_bytes_per_pic_denom : 0
   max_bits_per_mb_denom : 0
   log2_max_mv_length_horizontal : 0
   log2_max_mv_length_vertical : 0
   num_reorder_frames : 0
   max_dec_frame_buffering : 0
=== HRD ===
 cpb_cnt_minus1 : 0
 bit_rate_scale : 0
 cpb_size_scale : 0
   bit_rate_value_minus1[0] : 0
   cpb_size_value_minus1[0] : 0
   cbr_flag[0] : 0
 initial_cpb_removal_delay_length_minus1 : 0
 cpb_removal_delay_length_minus1 : 0
 dpb_output_delay_length_minus1 : 0
 time_offset_length : 0

我想这与亮度和色度块大小有关，我已经能够计算出 SubWidthC\SubHeightC 和 MbWidthC\MbHeightC.但我仍然很困惑接下来要做什么.

I guess it has something to do with luma and chorma macrblocks size I've been able to calculate SubWidthC\SubHeightC and MbWidthC\MbHeightC. But i'm still confused what to do next.

感谢您的任何帮助或指导最好的问候团队

Thank you for any kind of help or direction Best regards teamol

推荐答案

您好，首先您对 SPS 的解析不正确，因此您需要解决该问题.如果您正确解析它，那么您将拥有

Hello first of all you are parsing SPS incorrectly so you need to fix that. If you parse it correctly then you will have

pic_width_in_mbs_minus1 : 79
pic_height_in_map_units_minus1 : 44
frame_mbs_only_flag : 1
frame_cropping_flag : 0

如果您使用公式计算宽度和高度，那么您实际上将获得 1280x720

If you calculate width and height using your formula then you will actualy have 1280x720

无论如何，您应该使用 SubWidth 和 SubHeight 计算高度和宽度，如下所示:

Anyway you should calculate height and width using SubWidth and SubHeight as follows:

int SubWidthC;
int SubHeightC;

if (sps->chroma_format_idc == 0 && sps->separate_colour_plane_flag == 0) { //monochrome
    SubWidthC = SubHeightC = 0;
}
else if (sps->chroma_format_idc == 1 && sps->separate_colour_plane_flag == 0) { //4:2:0 
    SubWidthC = SubHeightC = 2;
}
else if (sps->chroma_format_idc == 2 && sps->separate_colour_plane_flag == 0) { //4:2:2 
    SubWidthC = 2;
    SubHeightC = 1;
}
else if (sps->chroma_format_idc == 3) { //4:4:4
    if (sps->separate_colour_plane_flag == 0) {
        SubWidthC = SubHeightC = 1;
    }
    else if (sps->separate_colour_plane_flag == 1) {
        SubWidthC = SubHeightC = 0;
    }
}

int PicWidthInMbs = sps->pic_width_in_mbs_minus1 + 1;

int PicHeightInMapUnits = sps->pic_height_in_map_units_minus1 + 1;
int FrameHeightInMbs = (2 - sps->frame_mbs_only_flag) * PicHeightInMapUnits;

int crop_left = 0;
int crop_right = 0;
int crop_top = 0;
int crop_bottom = 0;

if (sps->frame_cropping_flag) {
    crop_left = sps->frame_crop_left_offset;
    crop_right = sps->frame_crop_right_offset;
    crop_top = sps->frame_crop_top_offset;
    crop_bottom = sps->frame_crop_bottom_offset;
}

int width = PicWidthInMbs * 16 - SubWidthC * (crop_left + crop_right);
int height = FrameHeightInMbs * 16 - SubHeightC * (2 - sps->frame_mbs_only_flag) * (crop_top + crop_bottom);

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