EasyRTMP是将H264流以及AAC流以RTMP协议推送到RTMP服务器上进行直播。EasyRTMP推送库中会从H264流中提取中SPS、PPS进行解析，开发的时候遇到过有些SPS解析有误，获取到的宽高不正确，导致播放的时候画面被拉长的问题。下面给出一份比较完善的SPS解析
SPS解析
定义sps结构
typedef struct
{
int i_id;
int i_profile_idc;
int i_level_idc;
int b_constraint_set0;
int b_constraint_set1;
int b_constraint_set2;
int i_chroma_format_idc;
int i_log2_max_frame_num;
int i_poc_type;
/* poc 0 */
int i_log2_max_poc_lsb;
/* poc 1 */
int b_delta_pic_order_always_zero;
int i_offset_for_non_ref_pic;
int i_offset_for_top_to_bottom_field;
int i_num_ref_frames_in_poc_cycle;
int i_offset_for_ref_frame[256];
int i_num_ref_frames;
int b_gaps_in_frame_num_value_allowed;
int i_mb_width;
int i_mb_height;
int b_frame_mbs_only;
int b_mb_adaptive_frame_field;
int b_direct8x8_inference;
int b_crop;
struct
{
int i_left;
int i_right;
int i_top;
int i_bottom;
} crop;
int b_vui;
struct
{
int b_aspect_ratio_info_present;
int i_sar_width;
int i_sar_height;
int b_overscan_info_present;
int b_overscan_info;
int b_signal_type_present;
int i_vidformat;
int b_fullrange;
int b_color_description_present;
int i_colorprim;
int i_transfer;
int i_colmatrix;
int b_chroma_loc_info_present;
int i_chroma_loc_top;
int i_chroma_loc_bottom;
int b_timing_info_present;
int i_num_units_in_tick;
int i_time_scale;
int b_fixed_frame_rate;
int nal_hrd_parameters_present_flag;
int vcl_hrd_parameters_present_flag;
int pic_struct_present_flag;
int b_bitstream_restriction;
int b_motion_vectors_over_pic_boundaries;
int i_max_bytes_per_pic_denom;
int i_max_bits_per_mb_denom;
int i_log2_max_mv_length_horizontal;
int i_log2_max_mv_length_vertical;
int i_num_reorder_frames;
int i_max_dec_frame_buffering;
/* FIXME to complete */
} vui;
int b_qpprime_y_zero_transform_bypass;
int scaling_matrix_present;
uint8_t scaling_matrix4[6][16];
uint8_t scaling_matrix8[6][64];
} h264_sps_t;解析SPS数据，得到h264_sps_t结构的数据
/* return -1 if invalid, else the id */
int h264_sps_read( unsigned char *nal, int nal_len, h264_sps_t *sps)
{
int i_profile_idc;
int i_level_idc;
int b_constraint_set0;
int b_constraint_set1;
int b_constraint_set2;
int id;
bs_t bs;
bs_t *s = &bs;
sps->scaling_matrix_present = 0;
bs_init( &bs, nal+1, nal_len-1 );
//P264_TRACE_ADDRESS();
i_profile_idc = bs_read( s, 8 );
//_TRACE2("SPS: profile_idc = %d\n", i_profile_idc);
b_constraint_set0 = bs_read( s, 1 );
b_constraint_set1 = bs_read( s, 1 );
b_constraint_set2 = bs_read( s, 1 );
bs_skip( s, 5 ); /* reserved */
//P264_TRACE_ADDRESS();
i_level_idc = bs_read( s, 8 );
//_TRACE2("SPS: level_idc = %d\n", i_level_idc);
id = bs_read_ue( s );
if( bs_eof( s ) || id >= 32 )
{
/* the sps is invalid, no need to corrupt sps_array[0] */
return -1;
}
sps->i_id = id;
/* put pack parsed value */
sps->i_profile_idc = i_profile_idc;
sps->i_level_idc = i_level_idc;
sps->b_constraint_set0 = b_constraint_set0;
sps->b_constraint_set1 = b_constraint_set1;
sps->b_constraint_set2 = b_constraint_set2;
if(sps->i_profile_idc >= 100){ //high profile
sps->i_chroma_format_idc= bs_read_ue( s );
if(sps->i_chroma_format_idc >= 32 )
return -1;
if(sps->i_chroma_format_idc == 3)
bs_read( s, 1 );//residual_color_transform_flag
//sps->bit_depth_luma = get_ue_golomb(&s->gb) + 8;
//sps->bit_depth_chroma = get_ue_golomb(&s->gb) + 8;
//sps->transform_bypass = get_bits1(&s->gb);
/* bit_depth_luma_minus8 */
bs_read_ue( s );
/* bit_depth_chroma_minus8 */
bs_read_ue( s );
/* qpprime_y_zero_transform_bypass_flag */
bs_skip( s, 1 );
/* seq_scaling_matrix_present_flag */
int seq_scaling_matrix_present_flag = bs_read( s, 1 );
//decode_scaling_matrices(s, sps, NULL, 1, sps->scaling_matrix4, sps->scaling_matrix8);
if (seq_scaling_matrix_present_flag)
{
for( int i = 0; i < ((3 != sps->i_chroma_format_idc) ? 8 : 12); i++ )
{
/* seq_scaling_list_present_flag[i] */
seq_scaling_matrix_present_flag = bs_read( s, 1 );
if( !seq_scaling_matrix_present_flag )
continue;
const int i_size_of_scaling_list = (i < 6 ) ? 16 : 64;
/* scaling_list (...) */
int i_lastscale = 8;
int i_nextscale = 8;
for( int j = 0; j < i_size_of_scaling_list; j++ )
{
if( i_nextscale != 0 )
{
/* delta_scale */
seq_scaling_matrix_present_flag = bs_read_se( s );
i_nextscale = ( i_lastscale + seq_scaling_matrix_present_flag + 256 ) % 256;
/* useDefaultScalingMatrixFlag = ... */
}
/* scalinglist[j] */
i_lastscale = ( i_nextscale == 0 ) ? i_lastscale : i_nextscale;
}
}
}
}
//sps->i_log2_max_frame_num = bs_read_ue( s ) + 4;
//sps->i_log2_max_frame_num = 2^(bs_read_ue( s ) + 4);
sps->i_log2_max_frame_num = bs_read_ue( s );
sps->i_poc_type = bs_read_ue( s );
if( sps->i_poc_type == 0 )
{
sps->i_log2_max_poc_lsb = bs_read_ue( s ) + 4;
}
else if( sps->i_poc_type == 1 )
{
int i;
sps->b_delta_pic_order_always_zero = bs_read( s, 1 );
sps->i_offset_for_non_ref_pic = bs_read_se( s );
sps->i_offset_for_top_to_bottom_field = bs_read_se( s );
sps->i_num_ref_frames_in_poc_cycle = bs_read_ue( s );
if( sps->i_num_ref_frames_in_poc_cycle > 256 )
{
/* FIXME what to do */
sps->i_num_ref_frames_in_poc_cycle = 256;
}
for( i = 0; i < sps->i_num_ref_frames_in_poc_cycle; i++ )
{
sps->i_offset_for_ref_frame[i] = bs_read_se( s );
}
}
else if( sps->i_poc_type > 2 )
{
goto error;
}
sps->i_num_ref_frames = bs_read_ue( s );
//_TRACE2("SPS: num_ref_frames = %d\n", sps->i_num_ref_frames);
sps->b_gaps_in_frame_num_value_allowed = bs_read( s, 1 );
sps->i_mb_width = bs_read_ue( s ) + 1;
//_TRACE2("SPS: mb_width = %d\n", sps->i_mb_width);
sps->i_mb_height= bs_read_ue( s ) + 1;
//_TRACE2("SPS: mb_height = %d\n", sps->i_mb_height);
sps->b_frame_mbs_only = bs_read( s, 1 );
if( !sps->b_frame_mbs_only )
{
sps->b_mb_adaptive_frame_field = bs_read( s, 1 );
}
else
{
sps->b_mb_adaptive_frame_field = 0;
}
sps->b_direct8x8_inference = bs_read( s, 1 );
sps->b_crop = bs_read( s, 1 );
if( sps->b_crop )
{
sps->crop.i_left = bs_read_ue( s );
sps->crop.i_right = bs_read_ue( s );
sps->crop.i_top = bs_read_ue( s );
sps->crop.i_bottom= bs_read_ue( s );
}
else
{
sps->crop.i_left = 0;
sps->crop.i_right = 0;
sps->crop.i_top = 0;
sps->crop.i_bottom= 0;
}
sps->b_vui = bs_read( s, 1 );
if( sps->b_vui )
{
/* FIXME */
//_TRACE2( "decode vui %d\n", bs_pos(s) );
decode_vui_parameters(s, sps);
}
if( bs_eof( s ) )
{
/* no rbsp trailing */
//_TRACE2( "incomplete SPS\n" );
sps->i_id = -1;
return -1000;
}
return id;
error:
/* invalidate this sps */
sps->i_id = -1;
return -1;
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