verify.c
资源名称:mpeg2编解码.zip [点击查看]
上传用户:hkgotone
上传日期:2013-02-17
资源大小:293k
文件大小:8k
源码类别:
Windows Mobile
开发平台:
C/C++
- /* verify.c
- *
- * Bitstream verification routines
- *
- *
- */
- #ifdef VERIFY
- #include <stdio.h>
- #include <stdlib.h>
- #include <ctype.h>
- #include <fcntl.h>
- #include <math.h> /* needed for ceil() */
- #include "config.h"
- #include "global.h"
- /* #define DEBUG */
- #ifdef DEBUG
- #define PC
- #endif
- #ifdef PC
- #include <conio.h> /* needed for getch() */
- #endif /* PC */
- /*
- Check picture headers: due to the VBV definition of picture data,
- this routine must be called immediately before any picture data
- is parsed. (before the first slice start code, including any slice
- start code stuffing).
- */
- static void Check_VBV_Delay _ANSI_ARGS_((int Bitstream_Framenum, int Sequence_Framenum));
- void Check_Headers(Bitstream_Framenum, Sequence_Framenum)
- int Bitstream_Framenum;
- int Sequence_Framenum;
- {
- if((!low_delay)&&(vbv_delay!=0)&&(vbv_delay!=0xFFFF))
- Check_VBV_Delay(Bitstream_Framenum, Sequence_Framenum);
- /* clear out the header tracking variables so we have an accurate
- count next time */
- Clear_Verify_Headers();
- }
- /*
- * Verify vbv_delay value in picture header
- * (low_delay==1 checks not implemented. this does not exhaustively test all
- * possibilities suggested in ISO/IEC 13818-2 Annex C. It only checks
- * for constant rate streams)
- *
- * Q:how do we tell a variable rate stream from a constant rate stream anyway?
- * it's not as simple as vbv_delay==0xFFFF, since we need meaningful
- * vbv_delay values to calculate the piecewise rate in the first place!
- *
- * Also: no special provisions at the beginning or end of a sequence
- */
- static void Check_VBV_Delay(Bitstream_Framenum, Sequence_Framenum)
- int Bitstream_Framenum;
- int Sequence_Framenum;
- {
- double B; /* buffer size */
- double Bn; /* buffer fullness for picture n */
- double R; /* bitrate */
- double I; /* time interval (t[n+1] - t[n]) */
- double T; /* inverse of the frame rate (frame period) */
- int d;
- int internal_vbv_delay;
- static int previous_IorP_picture_structure;
- static int previous_IorP_repeat_first_field;
- static int previous_IorP_top_field_first;
- static int previous_vbv_delay;
- static int previous_bitstream_position;
- static double previous_Bn;
- static double E; /* maximum quantization error or mismatch */
- if((Sequence_Framenum==0)&&(!Second_Field))
- { /* first coded picture of sequence */
- R = bit_rate;
- /* the initial buffer occupancy is taken on faith
- that is, we believe what is transmitted in the first coded picture header
- to be the true/actual buffer occupancy */
- Bn = (R * (double) vbv_delay) / 90000.0;
- B = 16 * 1024 * vbv_buffer_size;
- /* maximum quantization error in bitrate (bit_rate_value is quantized/
- rounded-up to units of 400 bits/sec as per ISO/IEC 13818-2
- section 6.3.3 */
- E = (400.0/frame_rate) + 400;
- #ifdef DEBUG
- printf("vbv_buffer_size (B) = %.0f, Bn=%f, E=%f, nbitrate=%f, vbv_delay=%d frame_rate=%fn",
- B, Bn, E, bit_rate, vbv_delay, frame_rate);
- #endif
- }
- else /* not the first coded picture of sequence */
- {
- /* derive the interval (I). The interval tells us how many constant rate bits
- * will have been downloaded to the buffer during the current picture period
- *
- * interval assumes that:
- * 1. whilst we are decoding the current I or P picture, we are displaying
- * the previous I or P picture which was stored in the reorder
- * buffer (pointed to by forward_reference_frame in this implementation)
- *
- * 2. B pictures are output ("displayed") at the time when they are decoded
- *
- */
- if(progressive_sequence) /* Annex C.9 (progressive_sequence==1, low_delay==0) */
- {
- T = 1/frame_rate; /* inverse of the frame rate (frame period) */
- if(picture_coding_type==B_TYPE)
- {
- if(repeat_first_field==1)
- {
- if(top_field_first==1)
- I = T*3; /* three frame periods */
- else
- I = T*2; /* two frame periods */
- }
- else
- I = T; /* one frame period */
- }
- else /* P or I frame */
- {
- if(previous_IorP_repeat_first_field==1)
- {
- if(previous_IorP_top_field_first==1)
- I = 3*T;
- else
- I = 2*T;
- }
- else
- I = T;
- }
- }
- else /* Annex C.11 (progressive_sequence==0, low_delay==0) */
- {
- T = 1/(2*frame_rate); /* inverse of two times the frame rate (field period) */
- if(picture_coding_type==B_TYPE)
- {
- if(picture_structure==FRAME_PICTURE)
- {
- if(repeat_first_field==0)
- I = 2*T; /* two field periods */
- else
- I = 3*T; /* three field periods */
- }
- else /* B field */
- {
- I = T; /* one field period */
- }
- }
- else /* I or P picture */
- {
- if(picture_structure==FRAME_PICTURE)
- {
- if(previous_IorP_repeat_first_field==0)
- I = 2*T;
- else
- I = 3*T;
- }
- else
- {
- if(Second_Field==0) /* first field of current frame */
- I = T;
- else /* second field of current frame */
- {
- /* formula: previous I or P display period (2*T or 3*T) minus the
- very recent decode period (T) of the first field of the current
- frame */
- if(previous_IorP_picture_structure!=FRAME_PICTURE
- || previous_IorP_repeat_first_field==0)
- I = 2*T - T; /* a net of one field period */
- else if(previous_IorP_picture_structure==FRAME_PICTURE
- && previous_IorP_repeat_first_field==1)
- I = 3*T - T; /* a net of two field periods */
- }
- }
- }
- }
- /* derive coded size of previous picture */
- d = ld->Bitcnt - previous_bitstream_position;
- /* Rate = Distance/Time */
- /* piecewise constant rate (variable rate stream) calculation
- * R = ((double) d /((previous_vbv_delay - vbv_delay)/90000 + I));
- */
- R = bit_rate;
- /* compute buffer fullness just before removing picture n
- *
- * Bn = previous_Bn + (I*R) - d; (recursive formula)
- *
- * where:
- *
- * n is the current picture
- *
- * Bn is the buffer fullness for the current picture
- *
- * previous_Bn is the buffer fullness of the previous picture
- *
- * (I*R ) is the bits accumulated during the current picture
- * period
- *
- * d is the number of bits removed during the decoding of the
- * previous picture
- */
- Bn = previous_Bn + (I*R) - d;
- /* compute internally derived vbv_delay (rouding up with ceil()) */
- internal_vbv_delay = (int) ceil((90000 * Bn / bit_rate));
- #ifdef DEBUG
- printf("nvbv_delay: internal=%d, bitstream=%dn", internal_vbv_delay, vbv_delay);
- printf("Bn=%f, prevBn=%f, I=%f, R=%f, d=%dn", Bn, previous_Bn, I, R, d);
- printf("frame(%d), pictstruct(%d), picttype(%d)n", Sequence_Framenum,
- picture_structure, picture_coding_type);
- /* report error */
- if(internal_vbv_delay != vbv_delay)
- {
- printf("WARNING: internal_vbv_delay(%d) != vbv_delay(%d)n",
- internal_vbv_delay, vbv_delay);
- }
- #endif
- } /* not the first coded picture of sequence */
- #ifdef PC
- getch();
- #endif /* PC */
- /* update generic tracking variables */
- previous_bitstream_position = ld->Bitcnt ;
- previous_vbv_delay = vbv_delay;
- previous_Bn = Bn;
- /* reference picture: reordered/delayed output picture */
- if(picture_coding_type!=B_TYPE)
- {
- previous_IorP_repeat_first_field = repeat_first_field;
- previous_IorP_top_field_first = top_field_first;
- previous_IorP_picture_structure = picture_structure;
- }
- }
- /* variables to keep track of the occurance of redundant headers between pictures */
- void Clear_Verify_Headers()
- {
- verify_sequence_header = 0;
- verify_group_of_pictures_header = 0;
- verify_picture_header = 0;
- verify_slice_header = 0;
- verify_sequence_extension = 0;
- verify_sequence_display_extension = 0;
- verify_quant_matrix_extension = 0;
- verify_sequence_scalable_extension = 0;
- verify_picture_display_extension = 0;
- verify_picture_coding_extension = 0;
- verify_picture_spatial_scalable_extension = 0;
- verify_picture_temporal_scalable_extension = 0;
- verify_copyright_extension = 0;
- }
- #endif /* VERIFY */