x264的nal流程.doc

x264中的NAL流程 目前，主要是在分析NAL，做抓包实验，所以对NAL的格式要求比较高，这个过程中读了新一代视频编码，以前也读过，这是没有遇到实际的问题，读的时候也是似懂非懂的，囫囵吞枣，现在要分析，要用了才知道这些相关文档是要好好读的，ES流也是要好好分析的。在上一篇中关于函数指针和指针函数的理论知识中，我主要是来看看x264中的NAL是怎么在封装的。在x264中使用的函数指针，关于NAL部分的下面的一些：static int (*p_write_nalu)( hnd_t handle, uint8_t *p_nal, int i_size );，在这里可以看到p_write_nalu)是一个指针函数，p_write_nalu = write_nalu_bsf;即对于p_write_nalu其所指向的函数write_nalu_bsf，类似的还有：p_write_nalu = write_nalu_mp4;p_write_nalu = write_nalu_mkv;/每一个NALU都是由header+payload组成的，在header的结构是可以参考264的相关文档enum nal_unit_type_eNAL_UNKNOWN = 0,NAL_SLICE = 1,NAL_SLICE_DPA = 2,NAL_SLICE_DPB = 3,NAL_SLICE_DPC = 4,NAL_SLICE_IDR = 5, /* ref_idc != 0 */NAL_SEI = 6, /* ref_idc = 0 */NAL_SPS = 7,NAL_PPS = 8,NAL_AUD = 9,/* ref_idc = 0 for 6,9,10,11,12 */;enum nal_priority_eNAL_PRIORITY_DISPOSABLE = 0,NAL_PRIORITY_LOW = 1,NAL_PRIORITY_HIGH = 2,NAL_PRIORITY_HIGHEST = 3,;/NAL结构typedef structint i_ref_idc; /* nal_priority_e */int i_type; /* nal_unit_type_e */* Size of payload in bytes. */int i_payload; /负载的大小/* If param-b_annexb is set, Annex-B bytestream with 4-byte startcode.* Otherwise, startcode is replaced with a 4-byte size.* This size is the size used in mp4/similar muxing; it is equal to i_payload-4 */uint8_t *p_payload;/如果是字节流格式的NAL时所用到的前缀4bytes x264_nal_t;下面主要是跟踪x264，得到NAL的封装流程，如下：1. /NALstatic void x264_nal_start( x264_t *h, int i_type, int i_ref_idc )x264_nal_t *nal = &h-out.nalh-out.i_nal;nal-i_ref_idc = i_ref_idc;nal-i_type = i_type;nal-i_payload= 0;nal-p_payload= &h-out.p_bitstreambs_pos( &h-out.bs ) / 8;/下面是对bs_pos函数的注解static inline int bs_pos( bs_t *s )return( 8 * (s-p - s-p_start) + (WORD_SIZE*8) - s-i_left ); / /获取当前的NALU的地址?- s-i_left/bs_s的结构typedef struct bs_suint8_t *p_start;uint8_t *p;uint8_t *p_end;intptr_t cur_bits;int i_left; /* i_count number of available bits */int i_bits_encoded; /* RD only */ bs_t;2.static int x264_encoder_encapsulate_nals( x264_t *h ) /NAL封装int nal_size = 0, i;uint8_t *nal_buffer;for( i = 0; i out.i_nal; i+ )nal_size += h-out.nali.i_payload;/* Worst-case NAL unit escaping: reallocate the buffer if its too small. */if( h-nal_buffer_size out.i_nal * 4 )uint8_t *buf = x264_malloc( nal_size * 2 + h-out.i_nal * 4 );if( !buf )return -1;x264_free( h-nal_buffer );h-nal_buffer = buf;nal_buffer = h-nal_buffer;for( i = 0; i out.i_nal; i+ )int size = x264_nal_encode( nal_buffer, h-param.b_annexb, &h-out.nali );h-out.nali.i_payload = size;h-out.nali.p_payload = nal_buffer;nal_buffer += size;return nal_buffer - h-nal_buffer;3.在2.中有：int x264_nal_encode( uint8_t *dst, int b_annexb, x264_nal_t *nal )uint8_t *src = nal-p_payload; /为了同意结构还是将字节流格式的前缀作为指针的初始值uint8_t *end = nal-p_payload + nal-i_payload;uint8_t *orig_dst = dst;int i_count = 0, size;/* long nal start code (we always use long ones) */if( b_annexb ) /这里是进行字节流格式的码流编码，有开始前缀码，对于RTP封装则不需要前缀码*dst+ = 0x00;*dst+ = 0x00;*dst+ = 0x00;*dst+ = 0x01;else /* save room for size later */dst += 4;/* nal header */*dst+ = ( 0x00 i_ref_idc i_type;/第一个bit的设置是由编码器自己控制的while( src end )if( i_count = 2 & *src 24;orig_dst1 = size16;orig_dst2 = size 8;orig_dst3 = size 0;return size+4; /+44.static int x264_nal_end( x264_t *h )x264_nal_t *nal = &h-out.nalh-out.i_nal;nal-i_payload = &h-out.p_bitstreambs_pos( &h-out.bs )/ 8 - nal -p_payload;h-out.i_nal+;/* if number of allocated nals is not enough, re-allocate a larger one. */if( h-out.i_nal = h-out.i_nals_allocated )x264_nal_t *new_out = x264_malloc( sizeof(x264_nal_t) * (h-out.i_nals_allocated*2) );if( !new_out )return -1;memcpy( new_out, h-out.nal, sizeof(x264_nal_t) * (h-out.i_nals_allocated) );x264_free( h-out.nal );h-out.nal = new_out;h-out.i_nals_allocated *= 2;return 0;5.p_write_naluint write_nalu_bsf( hnd_t handle, uint8_t *p_nalu, int i_size )if( fwrite( p_nalu, i_size, 1, (FILE*)handle ) 0 ) /就是把p_nalu里面的1*i_size的字节输出到handle里面return i_size;return -1;实验跟踪：在编码第一个I帧的时候，要编码的NALU的个数为4个，这里主要是指编码的类型为：SEI,SPS,PPS,I帧的NAL的编码，对于一个I帧，也就是对这个GOP中的图像序列参数，图像参数进行编码，即有如下：/* Write SPS and PPS */if( i_nal_type = NAL_SLICE_IDR & h-param.b_repeat_headers )if( h-fenc-i_frame = 0 )/* identify ourself */x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE );if( x264_sei_version_write( h, &h-out.bs ) )return -1;if( x264_nal_end( h ) )return -1;overhead += h-out.nalh-out.i_nal-1.i_payload + NALU_OVERHEAD;/* generate sequence parameters */x264_nal_start( h, NAL_SPS, NAL_PRIORITY_HIGHEST );x264_sps_write( &h-out.bs, h-sps );if( x264_nal_end( h ) )return -1;overhead += h-out.nalh-out.i_nal-1.i_payload + NALU_OVERHEAD;/* generate picture parameters */x264_nal_start( h, NAL_PPS, NAL_PRIORITY_HIGHEST );x264_pps_write( &h-out.bs, h-pps );if( x264_nal_end( h ) )return -1;overhead += h-out.nalh-out.i_nal-1.i_payload + NALU_OVERHEAD;int x264_encoder_headers( x264_t *h, x264_nal_t *pp_nal, int *pi_nal )int frame_size = 0;/* init bitstream context */h-out.i_nal = 0;bs_init( &h-out.bs, h-out.p_bitstream, h-out.i_bitstream );/* Write SEI, SPS and PPS. */x264_nal_start( h, NAL_SEI, NAL_PRIORITY_DISPOSABLE );if( x264_sei_version_write( h, &h-out.bs ) )return -1;if( x264_nal_end( h ) )return -1;/* generate sequence parameters */x264_nal_start( h, NAL_SPS, NAL_PRIORITY_HIGHEST );x264_sps_write( &h-out.bs, h-sps );if( x264_nal_end( h ) )return -1;/* generate picture parameters */x264_nal_start( h, NAL_PPS, NAL_PRIORITY_HIGHEST );x264_pps_write( &h-out.bs, h-pps );if( x264_nal_end( h ) )return -1;bs_flush( &h-out.bs );frame_size = x264_encoder_encapsulate_nals( h );/* now set output*/*pi_nal =