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1624 giacomo 1
/* verify.c
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 *
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 * Bitstream verification routines
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 *
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 *
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 */
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#ifdef VERIFY 
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#include <stdlib.h>
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#include <math.h>     /* needed for ceil() */
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#include "config.h"
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#include "global.h"
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/* #define DEBUG  */
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#ifdef DEBUG
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#define PC 
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#endif
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#ifdef PC
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#include <conio.h>    /* needed for getch() */
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#endif /* PC */
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/*
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   Check picture headers:  due to the VBV definition of picture data,
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   this routine must be called immediately before any picture data
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   is parsed. (before the first slice start code, including any slice
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   start code stuffing).
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*/
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static void Check_VBV_Delay _ANSI_ARGS_((int Bitstream_Framenum, int Sequence_Framenum));
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void Check_Headers(Bitstream_Framenum, Sequence_Framenum)
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int Bitstream_Framenum;
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int Sequence_Framenum;
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{
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  if((!low_delay)&&(vbv_delay!=0)&&(vbv_delay!=0xFFFF))
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    Check_VBV_Delay(Bitstream_Framenum, Sequence_Framenum);
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  /* clear out the header tracking variables so we have an accurate
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     count next time */
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  Clear_Verify_Headers();
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}
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/*
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 * Verify vbv_delay value in picture header
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 * (low_delay==1 checks not implemented. this does not exhaustively test all
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 *  possibilities suggested in ISO/IEC 13818-2 Annex C.  It only checks
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 *  for constant rate streams)
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 *
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 * Q:how do we tell a variable rate stream from a constant rate stream anyway?
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 *   it's not as simple as vbv_delay==0xFFFF, since we need meaningful
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 *   vbv_delay values to calculate the piecewise rate in the first place!
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 *
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 * Also: no special provisions at the beginning or end of a sequence
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 */
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static void Check_VBV_Delay(Bitstream_Framenum, Sequence_Framenum)
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int Bitstream_Framenum;
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int Sequence_Framenum;
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{
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  double B;   /* buffer size                   */
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  double Bn;  /* buffer fullness for picture n */
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  double R;   /* bitrate                       */
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  double I;   /* time interval (t[n+1] - t[n]) */
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  double T;   /* inverse of the frame rate (frame period) */
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74
  int d;
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  int internal_vbv_delay;
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77
  static int previous_IorP_picture_structure;
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  static int previous_IorP_repeat_first_field;
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  static int previous_IorP_top_field_first;
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  static int previous_vbv_delay;
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  static int previous_bitstream_position;
82
 
83
  static double previous_Bn;
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  static double E;      /* maximum quantization error or mismatch */
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87
 
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  if((Sequence_Framenum==0)&&(!Second_Field))
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  {  /* first coded picture of sequence */
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91
    R = bit_rate;
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    /* the initial buffer occupancy is taken on faith
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       that is, we believe what is transmitted in the first coded picture header
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       to be the true/actual buffer occupancy */
96
 
97
    Bn = (R * (double) vbv_delay) / 90000.0;
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    B = 16 * 1024 * vbv_buffer_size;
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    /* maximum quantization error in bitrate (bit_rate_value is quantized/
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       rounded-up to units of 400 bits/sec as per ISO/IEC 13818-2
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       section 6.3.3 */
104
 
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    E = (400.0/frame_rate) + 400;
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#ifdef DEBUG
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    cprintf("vbv_buffer_size (B) = %.0f, Bn=%f, E=%f, \nbitrate=%f, vbv_delay=%d frame_rate=%f\n",
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      B, Bn, E, bit_rate, vbv_delay, frame_rate);
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#endif
111
 
112
  }
113
  else /* not the first coded picture of sequence */
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  {
115
 
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    /* derive the interval (I).  The interval tells us how many constant rate bits
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     * will have been downloaded to the buffer during the current picture period
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     *
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     * interval assumes that:
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     *  1. whilst we are decoding the current I or P picture, we are displaying
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     *     the previous I or P picture which was stored in the reorder
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     *     buffer (pointed to by forward_reference_frame in this implementation)
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     *
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     *  2. B pictures are output ("displayed") at the time when they are decoded
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     *
126
     */
127
 
128
    if(progressive_sequence) /* Annex C.9 (progressive_sequence==1, low_delay==0) */
129
    {
130
 
131
      T = 1/frame_rate; /* inverse of the frame rate (frame period) */
132
 
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      if(picture_coding_type==B_TYPE)
134
      {
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        if(repeat_first_field==1)
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        {
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          if(top_field_first==1)
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            I = T*3;  /* three frame periods */
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          else
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            I = T*2;  /* two frame periods */
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        }
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        else
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          I = T;      /* one frame period */
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      }
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      else /* P or I frame */
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      {
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        if(previous_IorP_repeat_first_field==1)
148
        {
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          if(previous_IorP_top_field_first==1)
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            I = 3*T;
151
          else
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            I = 2*T;
153
        }
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        else
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          I = T;
156
      }
157
    }
158
    else /* Annex C.11 (progressive_sequence==0, low_delay==0) */
159
    {
160
 
161
      T = 1/(2*frame_rate); /* inverse of two times the frame rate (field period) */
162
 
163
      if(picture_coding_type==B_TYPE)
164
      {
165
        if(picture_structure==FRAME_PICTURE)
166
        {
167
          if(repeat_first_field==0)
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            I = 2*T;  /* two field periods */
169
          else
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            I = 3*T;  /* three field periods */
171
        }
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        else /* B field */
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        {
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          I = T;      /* one field period */
175
        }
176
      }
177
      else /* I or P picture */
178
      {
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        if(picture_structure==FRAME_PICTURE)
180
        {
181
          if(previous_IorP_repeat_first_field==0)
182
            I = 2*T;
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          else
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            I = 3*T;
185
        }
186
        else
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        {
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          if(Second_Field==0)  /* first field of current frame */
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            I = T;
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          else /* second field of current frame */
191
          {
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            /* formula: previous I or P display period (2*T or 3*T) minus the
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               very recent decode period (T) of the first field of the current
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               frame */
195
 
196
            if(previous_IorP_picture_structure!=FRAME_PICTURE
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              || previous_IorP_repeat_first_field==0)
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              I = 2*T - T;  /* a net of one field period */
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            else if(previous_IorP_picture_structure==FRAME_PICTURE
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              && previous_IorP_repeat_first_field==1)
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              I = 3*T - T;  /* a net of two field periods */
202
          }
203
        }
204
      }
205
    }
206
 
207
    /* derive coded size of previous picture */
208
    d  = ld->Bitcnt - previous_bitstream_position;
209
 
210
    /* Rate = Distance/Time */
211
 
212
    /* piecewise constant rate (variable rate stream) calculation
213
     * R =  ((double) d /((previous_vbv_delay - vbv_delay)/90000 + I));
214
     */
215
 
216
    R = bit_rate;
217
 
218
    /* compute buffer fullness just before removing picture n
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     *
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     * Bn = previous_Bn + (I*R) - d;     (recursive formula)
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     *
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     *   where:
223
     *
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     *    n           is the current picture
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     *
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     *    Bn          is the buffer fullness for the current picture
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     *
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     *    previous_Bn is the buffer fullness of the previous picture
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     *
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     *    (I*R )      is the bits accumulated during the current picture
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     *                period
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     *
233
     *    d           is the number of bits removed during the decoding of the
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     *                previous picture
235
     */
236
 
237
    Bn = previous_Bn + (I*R) - d;
238
 
239
    /* compute internally derived vbv_delay (rouding up with ceil()) */
240
    internal_vbv_delay = (int) ceil((90000 * Bn / bit_rate));
241
 
242
#ifdef DEBUG
243
    cprintf("\nvbv_delay: internal=%d, bitstream=%d\n", internal_vbv_delay, vbv_delay);
244
 
245
    cprintf("Bn=%f, prevBn=%f, I=%f, R=%f, d=%d\n", Bn, previous_Bn, I, R, d);
246
    cprintf("frame(%d), pictstruct(%d), picttype(%d)\n", Sequence_Framenum,
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      picture_structure, picture_coding_type);
248
 
249
    /* report error */
250
    if(internal_vbv_delay != vbv_delay)
251
    {
252
      cprintf("WARNING: internal_vbv_delay(%d) != vbv_delay(%d)\n",
253
        internal_vbv_delay, vbv_delay);
254
    }
255
#endif
256
 
257
  } /* not the first coded picture of sequence */
258
 
259
 
260
#ifdef PC
261
  getch();
262
#endif /* PC */
263
 
264
  /* update generic tracking variables */
265
  previous_bitstream_position = ld->Bitcnt ;
266
  previous_vbv_delay          = vbv_delay;
267
  previous_Bn                 = Bn;
268
 
269
  /* reference picture: reordered/delayed output picture */
270
  if(picture_coding_type!=B_TYPE)
271
  {
272
    previous_IorP_repeat_first_field = repeat_first_field;
273
    previous_IorP_top_field_first    = top_field_first;
274
    previous_IorP_picture_structure  = picture_structure;
275
  }
276
 
277
}
278
 
279
 
280
 
281
/* variables to keep track of the occurance of redundant headers between pictures */
282
void Clear_Verify_Headers()
283
{
284
  verify_sequence_header = 0;
285
  verify_group_of_pictures_header = 0;
286
  verify_picture_header = 0;
287
  verify_slice_header = 0;
288
  verify_sequence_extension = 0;
289
  verify_sequence_display_extension = 0;
290
  verify_quant_matrix_extension = 0;
291
  verify_sequence_scalable_extension = 0;
292
  verify_picture_display_extension = 0;
293
  verify_picture_coding_extension = 0;
294
  verify_picture_spatial_scalable_extension = 0;
295
  verify_picture_temporal_scalable_extension = 0;
296
  verify_copyright_extension = 0;
297
}
298
 
299
#endif /* VERIFY */
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