一步一步解析H.264码流的NALU(SPS,PSS,IDR)获取宽高和帧率
分析H.264码流的工具
CodecVisa，StreamEye以及VM Analyzer
NALU是由NALU头和RBSP数据组成，而RBSP可能是SPS，PPS，Slice或SEI
而且SPS位于第一个NALU，PPS位于第二个NALU
另外值得说一下的就是从Headers Info拷贝出来的数据当中”na”就是未定义的，也就是if条件没有覆盖的情况。
sps
pic_width_in_mbs_minus1 = 21
pic_height_in_mbs_minus1 = 17
分别表示图像的宽和高，以宏块（16x16）为单位的值减1
因此，实际的宽为 (21+1)*16 = 352
以上是针对宽高是16的整数倍的情况，当不是16整数倍时，frame_cropping_flag值为1，frame_mbs_only_flag为1，公式如下：
// 宽高计算公式
width = (sps->pic_width_in_mbs_minus1+1) * 16;
height = (2 - sps->frame_mbs_only_flag)* (sps->pic_height_in_map_units_minus1 +1) * 16);
if(sps->frame_cropping_flag)
{
unsigned int crop_unit_x;
unsigned int crop_unit_y;
if (0 == sps->chroma_format_idc) // monochrome
{
crop_unit_x = 1;
crop_unit_y = 2 - sps->frame_mbs_only_flag;
}
else if (1 == sps->chroma_format_idc) // 4:2:0
{
crop_unit_x = 2;
crop_unit_y = 2 * (2 - sps->frame_mbs_only_flag);
}
else if (2 == sps->chroma_format_idc) // 4:2:2
{
crop_unit_x = 2;
crop_unit_y = 2 - sps->frame_mbs_only_flag;
}
else // 3 == sps.chroma_format_idc // 4:4:4
{
crop_unit_x = 1;
crop_unit_y = 2 - sps->frame_mbs_only_flag;
}
width -= crop_unit_x * (sps->frame_crop_left_offset + sps->frame_crop_right_offset);
height -= crop_unit_y * (sps->frame_crop_top_offset + sps->frame_crop_bottom_offset);
}
ff_h264_decode_seq_parameter_set
ff_h264_decode_picture_parameter_set
https://cardinalpeak.com/blog/the-h-264-sequence-parameter-set/
最好参考：H.264官方中文版.pdf7.3.2.1节对比查看
| Parameter Name | Type | Value | Comments |
| forbidden_zero_bit | u(1) | 0 | Despite being forbidden, it must be set to 0! |
| nal_ref_idc | u(2) | 3 | 3 means it is “important” (this is an SPS) |
| nal_unit_type | u(5) | 7 | Indicates this is a sequence parameter set |
|
|
|
|
|
| profile_idc | u(8) | 66 | Baseline profile |
|
|
|
|
|
| constraint_set0_flag | u(1) | 0 | We’re not going to honor constraints |
| constraint_set1_flag | u(1) | 0 | We’re not going to honor constraints |
| constraint_set2_flag | u(1) | 0 | We’re not going to honor constraints |
| constraint_set3_flag | u(1) | 0 | We’re not going to honor constraints |
| reserved_zero_4bits | u(4) | 0 | Better set them to zero |
|
|
|
|
|
| level_idc | u(8) | 10 | Level 1, sec A.3.1 |
| seq_parameter_set_id | ue(v) | 0 | We’ll just use id 0. |
| log2_max_frame_num_minus4 | ue(v) | 0 | Let’s have as few frame numbers as possible |
| pic_order_cnt_type | ue(v) | 0 | Keep things simple |
| log2_max_pic_order_cnt_lsb_minus4 | ue(v) | 0 | Fewer is better. |
| num_ref_frames | ue(v) | 0 | We will only send I slices |
| gaps_in_frame_num_value_allowed_flag | u(1) | 0 | We will have no gaps |
| pic_width_in_mbs_minus_1 | ue(v) | 7 | SQCIF is 8 macroblocks wide |
| pic_height_in_map_units_minus_1 | ue(v) | 5 | SQCIF is 6 macroblocks high |
| frame_mbs_only_flag | u(1) | 1 | We will not to field/frame encoding |
| direct_8x8_inference_flag | u(1) | 0 | Used for B slices. We will not send B slices |
| frame_cropping_flag | u(1) | 0 | We will not do frame cropping |
| vui_prameters_present_flag | u(1) | 0 | We will not send VUI data |
| rbsp_stop_one_bit | u(1) | 1 | Stop bit. I missed this at first and it caused me much trouble. |
ff_h264_decode_seq_parameter_set解析：
skip_bits(&h->gb, 2);跳过两个位，表现为GetBitContext.index后移两个位置。
- 当前SPS的帧的宽 = (sps_info.pic_width_in_mbs_minus1 + 1) * 16
- 当前SPS的帧的高 = (sps_info.pic_height_in_map_units_minus1 + 1) * 16
extract the h.264 NAL units from the file using ffmpeg:
ffmpeg.exe -i Old Faithful.mp4 -vcodec copy -vbsf h264_mp4toannexb -an of.h264
获取帧率
https://github.com/leixiaohua1020/simplest_librtmp_example/blob/master/simplest_librtmp_send264/sps_decode.h
fps=time_scale/(2*num_units_in_tick);
30/(2*1)=15fps
fps=time_scale/(2*num_units_in_tick);
30/(2*1)=15fps
https://github.com/leixiaohua1020/h264_analysis
参考：
http://www.latelee.org/my-study/get-width-height-framerate-from-bitstream.html
宽高计算公式
分析H.264码流的工具
CodecVisa，StreamEye以及VM Analyzer
NALU是由NALU头和RBSP数据组成，而RBSP可能是SPS，PPS，Slice或SEI
而且SPS位于第一个NALU，PPS位于第二个NALU
另外值得说一下的就是从Headers Info拷贝出来的数据当中”na”就是未定义的，也就是if条件没有覆盖的情况。
sps
pic_width_in_mbs_minus1 = 21
pic_height_in_mbs_minus1 = 17
分别表示图像的宽和高，以宏块（16x16）为单位的值减1
因此，实际的宽为 (21+1)*16 = 352
以上是针对宽高是16的整数倍的情况，当不是16整数倍时，frame_cropping_flag值为1，frame_mbs_only_flag为1，公式如下：
// 宽高计算公式
width = (sps->pic_width_in_mbs_minus1+1) * 16;
height = (2 - sps->frame_mbs_only_flag)* (sps->pic_height_in_map_units_minus1 +1) * 16);
if(sps->frame_cropping_flag)
{
unsigned int crop_unit_x;
unsigned int crop_unit_y;
if (0 == sps->chroma_format_idc) // monochrome
{
crop_unit_x = 1;
crop_unit_y = 2 - sps->frame_mbs_only_flag;
}
else if (1 == sps->chroma_format_idc) // 4:2:0
{
crop_unit_x = 2;
crop_unit_y = 2 * (2 - sps->frame_mbs_only_flag);
}
else if (2 == sps->chroma_format_idc) // 4:2:2
{
crop_unit_x = 2;
crop_unit_y = 2 - sps->frame_mbs_only_flag;
}
else // 3 == sps.chroma_format_idc // 4:4:4
{
crop_unit_x = 1;
crop_unit_y = 2 - sps->frame_mbs_only_flag;
}
width -= crop_unit_x * (sps->frame_crop_left_offset + sps->frame_crop_right_offset);
height -= crop_unit_y * (sps->frame_crop_top_offset + sps->frame_crop_bottom_offset);
}
ff_h264_decode_seq_parameter_set
ff_h264_decode_picture_parameter_set
https://cardinalpeak.com/blog/the-h-264-sequence-parameter-set/
最好参考：H.264官方中文版.pdf7.3.2.1节对比查看
| Parameter Name | Type | Value | Comments |
| forbidden_zero_bit | u(1) | 0 | Despite being forbidden, it must be set to 0! |
| nal_ref_idc | u(2) | 3 | 3 means it is “important” (this is an SPS) |
| nal_unit_type | u(5) | 7 | Indicates this is a sequence parameter set |
|
|
|
|
|
| profile_idc | u(8) | 66 | Baseline profile |
|
|
|
|
|
| constraint_set0_flag | u(1) | 0 | We’re not going to honor constraints |
| constraint_set1_flag | u(1) | 0 | We’re not going to honor constraints |
| constraint_set2_flag | u(1) | 0 | We’re not going to honor constraints |
| constraint_set3_flag | u(1) | 0 | We’re not going to honor constraints |
| reserved_zero_4bits | u(4) | 0 | Better set them to zero |
|
|
|
|
|
| level_idc | u(8) | 10 | Level 1, sec A.3.1 |
| seq_parameter_set_id | ue(v) | 0 | We’ll just use id 0. |
| log2_max_frame_num_minus4 | ue(v) | 0 | Let’s have as few frame numbers as possible |
| pic_order_cnt_type | ue(v) | 0 | Keep things simple |
| log2_max_pic_order_cnt_lsb_minus4 | ue(v) | 0 | Fewer is better. |
| num_ref_frames | ue(v) | 0 | We will only send I slices |
| gaps_in_frame_num_value_allowed_flag | u(1) | 0 | We will have no gaps |
| pic_width_in_mbs_minus_1 | ue(v) | 7 | SQCIF is 8 macroblocks wide |
| pic_height_in_map_units_minus_1 | ue(v) | 5 | SQCIF is 6 macroblocks high |
| frame_mbs_only_flag | u(1) | 1 | We will not to field/frame encoding |
| direct_8x8_inference_flag | u(1) | 0 | Used for B slices. We will not send B slices |
| frame_cropping_flag | u(1) | 0 | We will not do frame cropping |
| vui_prameters_present_flag | u(1) | 0 | We will not send VUI data |
| rbsp_stop_one_bit | u(1) | 1 | Stop bit. I missed this at first and it caused me much trouble. |
ff_h264_decode_seq_parameter_set解析：
skip_bits(&h->gb, 2);跳过两个位，表现为GetBitContext.index后移两个位置。
- 当前SPS的帧的宽 = (sps_info.pic_width_in_mbs_minus1 + 1) * 16
- 当前SPS的帧的高 = (sps_info.pic_height_in_map_units_minus1 + 1) * 16
extract the h.264 NAL units from the file using ffmpeg:
ffmpeg.exe -i Old Faithful.mp4 -vcodec copy -vbsf h264_mp4toannexb -an of.h264
获取帧率
https://github.com/leixiaohua1020/simplest_librtmp_example/blob/master/simplest_librtmp_send264/sps_decode.h
fps=time_scale/(2*num_units_in_tick);
30/(2*1)=15fps
fps=time_scale/(2*num_units_in_tick);
30/(2*1)=15fps
https://github.com/leixiaohua1020/h264_analysis
参考：
http://www.latelee.org/my-study/get-width-height-framerate-from-bitstream.html
宽高计算公式