aboutsummaryrefslogtreecommitdiffhomepage
path: root/libmpdemux/yuv4mpeg.c
blob: 04b959e9dc3fb4d10eeb1b7878b8ea47b701804b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
/*
 *  yuv4mpeg.c:  Functions for reading and writing "new" YUV4MPEG streams
 *
 *  Copyright (C) 2001 Matthew J. Marjanovic <maddog@mir.com>
 *
 *  This file is ripped from the lavtools package (mjpeg.sourceforge.net)
 *  Ported to mplayer by Rik Snel <rsnel@cube.dyndns.org>
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version 2
 *  of the License, or (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 *
 */

#include "config.h"

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "yuv4mpeg.h"
#include "yuv4mpeg_intern.h"
#include "mp_msg.h"

static int _y4mparam_allow_unknown_tags = 1;  /* default is forgiveness */

static void *(*_y4m_alloc)(size_t bytes) = malloc;
static void (*_y4m_free)(void *ptr) = free;

int y4m_allow_unknown_tags(int yn) {
	int old = _y4mparam_allow_unknown_tags;
  	if (yn >= 0) _y4mparam_allow_unknown_tags = (yn) ? 1 : 0;
  	return old;
}



/*************************************************************************
 *
 * Convenience functions for fd read/write
 *
 *   - guaranteed to transfer entire payload (or fail)
 *   - returns:
 *               0 on complete success
 *               +(# of remaining bytes) on eof (for y4m_read)
 *               -(# of rem. bytes) on error (and ERRNO should be set)
 *     
 *************************************************************************/


ssize_t y4m_read(stream_t *s, char *buf, size_t len)
{
   ssize_t n;

   while (len > 0) {
     n = stream_read(s, buf, len);
     if (n <= 0) {
       /* return amount left to read */
       if (n == 0)
	 return len;  /* n == 0 --> eof */
       else
	 return -len; /* n < 0 --> error */
     }
     buf += n;
     len -= n;
   }
   return 0;
}


#if 0 /* not needed */
ssize_t y4m_write(int fd, char *buf, size_t len)
{
   ssize_t n;

   while (len > 0) {
     n = write(fd, buf, len);
     if (n < 0) return -len;  /* return amount left to write */
     buf += n;
     len -= n;
   }
   return 0;
}
#endif


/*************************************************************************
 *
 * "Extra tags" handling
 *
 *************************************************************************/


static char *y4m_new_xtag(void)
{
  return _y4m_alloc(Y4M_MAX_XTAG_SIZE);
}


void y4m_init_xtag_list(y4m_xtag_list_t *xtags)
{
  int i;
  xtags->count = 0;
  for (i = 0; i < Y4M_MAX_XTAGS; i++) {
    xtags->tags[i] = NULL;
  }
}


void y4m_fini_xtag_list(y4m_xtag_list_t *xtags)
{
  int i;
  for (i = 0; i < Y4M_MAX_XTAGS; i++) {
    if (xtags->tags[i] != NULL) {
      _y4m_free(xtags->tags[i]);
      xtags->tags[i] = NULL;
    }
  }
  xtags->count = 0;
}


void y4m_copy_xtag_list(y4m_xtag_list_t *dest, const y4m_xtag_list_t *src)
{
  int i;
  for (i = 0; i < src->count; i++) {
    if (dest->tags[i] == NULL) 
      dest->tags[i] = y4m_new_xtag();
    strncpy(dest->tags[i], src->tags[i], Y4M_MAX_XTAG_SIZE);
  }
  dest->count = src->count;
}



#if 0
static int y4m_snprint_xtags(char *s, int maxn, y4m_xtag_list_t *xtags)
{
  int i, room;
  
  for (i = 0, room = maxn - 1; i < xtags->count; i++) {
    int n = snprintf(s, room + 1, " %s", xtags->tags[i]);
    if ((n < 0) || (n > room)) return Y4M_ERR_HEADER;
    s += n;
    room -= n;
  }
  s[0] = '\n';  /* finish off header with newline */
  s[1] = '\0';  /* ...and end-of-string           */
  return Y4M_OK;
}
#endif


int y4m_xtag_count(const y4m_xtag_list_t *xtags)
{
  return xtags->count;
}


const char *y4m_xtag_get(const y4m_xtag_list_t *xtags, int n)
{
  if (n >= xtags->count)
    return NULL;
  else
    return xtags->tags[n];
}


int y4m_xtag_add(y4m_xtag_list_t *xtags, const char *tag)
{
  if (xtags->count >= Y4M_MAX_XTAGS) return Y4M_ERR_XXTAGS;
  if (xtags->tags[xtags->count] == NULL) {
    xtags->tags[xtags->count] = y4m_new_xtag();
  }
  strncpy(xtags->tags[xtags->count], tag, Y4M_MAX_XTAG_SIZE);
  (xtags->count)++;
  return Y4M_OK;
}


int y4m_xtag_remove(y4m_xtag_list_t *xtags, int n)
{
  int i;
  char *q;

  if ((n < 0) || (n >= xtags->count)) return Y4M_ERR_RANGE;
  q = xtags->tags[n];
  for (i = n; i < (xtags->count - 1); i++)
    xtags->tags[i] = xtags->tags[i+1];
  xtags->tags[i] = q;
  (xtags->count)--;
  return Y4M_OK;
}


int y4m_xtag_clearlist(y4m_xtag_list_t *xtags)
{
  xtags->count = 0;
  return Y4M_OK;
}


int y4m_xtag_addlist(y4m_xtag_list_t *dest, const y4m_xtag_list_t *src)
{
  int i, j;

  if ((dest->count + src->count) > Y4M_MAX_XTAGS) return Y4M_ERR_XXTAGS;
  for (i = dest->count, j = 0;
       j < src->count;
       i++, j++) {
    if (dest->tags[i] == NULL) 
      dest->tags[i] = y4m_new_xtag();
    strncpy(dest->tags[i], src->tags[i], Y4M_MAX_XTAG_SIZE);
  }
  dest->count += src->count;
  return Y4M_OK;
}  


/*************************************************************************
 *
 * Creators/destructors for y4m_*_info_t structures
 *
 *************************************************************************/


void y4m_init_stream_info(y4m_stream_info_t *info)
{
  if (info == NULL) return;
  /* initialize info */
  info->width = Y4M_UNKNOWN;
  info->height = Y4M_UNKNOWN;
  info->interlace = Y4M_UNKNOWN;
  info->framerate = y4m_fps_UNKNOWN;
  info->sampleaspect = y4m_sar_UNKNOWN;
  y4m_init_xtag_list(&(info->x_tags));
}


void y4m_copy_stream_info(y4m_stream_info_t *dest, y4m_stream_info_t *src)
{
  if ((dest == NULL) || (src == NULL)) return;
  /* copy info */
  dest->width = src->width;
  dest->height = src->height;
  dest->interlace = src->interlace;
  dest->framerate = src->framerate;
  dest->sampleaspect = src->sampleaspect;
  y4m_copy_xtag_list(&(dest->x_tags), &(src->x_tags));
}


void y4m_fini_stream_info(y4m_stream_info_t *info)
{
  if (info == NULL) return;
  y4m_fini_xtag_list(&(info->x_tags));
}


void y4m_si_set_width(y4m_stream_info_t *si, int width)
{
  si->width = width;
  si->framelength = (si->height * si->width) * 3 / 2;
}

int y4m_si_get_width(y4m_stream_info_t *si)
{ return si->width; }

void y4m_si_set_height(y4m_stream_info_t *si, int height)
{
  si->height = height; 
  si->framelength = (si->height * si->width) * 3 / 2;
}

int y4m_si_get_height(y4m_stream_info_t *si)
{ return si->height; }

void y4m_si_set_interlace(y4m_stream_info_t *si, int interlace)
{ si->interlace = interlace; }

int y4m_si_get_interlace(y4m_stream_info_t *si)
{ return si->interlace; }

void y4m_si_set_framerate(y4m_stream_info_t *si, y4m_ratio_t framerate)
{ si->framerate = framerate; }

y4m_ratio_t y4m_si_get_framerate(y4m_stream_info_t *si)
{ return si->framerate; }

void y4m_si_set_sampleaspect(y4m_stream_info_t *si, y4m_ratio_t sar)
{ si->sampleaspect = sar; }

y4m_ratio_t y4m_si_get_sampleaspect(y4m_stream_info_t *si)
{ return si->sampleaspect; }

int y4m_si_get_framelength(y4m_stream_info_t *si)
{ return si->framelength; }

y4m_xtag_list_t *y4m_si_xtags(y4m_stream_info_t *si)
{ return &(si->x_tags); }



void y4m_init_frame_info(y4m_frame_info_t *info)
{
  if (info == NULL) return;
  /* initialize info */
  y4m_init_xtag_list(&(info->x_tags));
}


void y4m_copy_frame_info(y4m_frame_info_t *dest, y4m_frame_info_t *src)
{
  if ((dest == NULL) || (src == NULL)) return;
  /* copy info */
  y4m_copy_xtag_list(&(dest->x_tags), &(src->x_tags));
}


void y4m_fini_frame_info(y4m_frame_info_t *info)
{
  if (info == NULL) return;
  y4m_fini_xtag_list(&(info->x_tags));
}



/*************************************************************************
 *
 * Tag parsing 
 *
 *************************************************************************/

int y4m_parse_stream_tags(char *s, y4m_stream_info_t *i)
{
  char *token, *value;
  char tag;
  int err;

  /* parse fields */
  for (token = strtok(s, Y4M_DELIM); 
       token != NULL; 
       token = strtok(NULL, Y4M_DELIM)) {
    if (token[0] == '\0') continue;   /* skip empty strings */
    tag = token[0];
    value = token + 1;
    switch (tag) {
    case 'W':  /* width */
      i->width = atoi(value);
      if (i->width <= 0) return Y4M_ERR_RANGE;
      break;
    case 'H':  /* height */
      i->height = atoi(value); 
      if (i->height <= 0) return Y4M_ERR_RANGE;
      break;
    case 'F':  /* frame rate (fps) */
      if ((err = y4m_parse_ratio(&(i->framerate), value)) != Y4M_OK)
	return err;
      if (i->framerate.n < 0) return Y4M_ERR_RANGE;
      break;
    case 'I':  /* interlacing */
      switch (value[0]) {
      case 'p':  i->interlace = Y4M_ILACE_NONE; break;
      case 't':  i->interlace = Y4M_ILACE_TOP_FIRST; break;
      case 'b':  i->interlace = Y4M_ILACE_BOTTOM_FIRST; break;
      case '?':
      default:
	i->interlace = Y4M_UNKNOWN; break;
      }
      break;
    case 'A':  /* sample (pixel) aspect ratio */
      if ((err = y4m_parse_ratio(&(i->sampleaspect), value)) != Y4M_OK)
	return err;
      if (i->sampleaspect.n < 0) return Y4M_ERR_RANGE;
      break;
    case 'X':  /* 'X' meta-tag */
      if ((err = y4m_xtag_add(&(i->x_tags), token)) != Y4M_OK) return err;
      break;
    default:
      /* possible error on unknown options */
      if (_y4mparam_allow_unknown_tags) {
	/* unknown tags ok:  store in xtag list and warn... */
	if ((err = y4m_xtag_add(&(i->x_tags), token)) != Y4M_OK) return err;
	mp_msg(MSGT_DEMUX, MSGL_WARN, "Unknown stream tag encountered:  '%s'\n", token);
      } else {
	/* unknown tags are *not* ok */
	return Y4M_ERR_BADTAG;
      }
      break;
    }
  }
  /* Error checking... width and height must be known since we can't
   * parse without them
   */
  if( i->width == Y4M_UNKNOWN || i->height == Y4M_UNKNOWN )
	  return Y4M_ERR_HEADER;
  /* ta da!  done. */
  return Y4M_OK;
}



static int y4m_parse_frame_tags(char *s, y4m_frame_info_t *i)
{
  char *token, *value;
  char tag;
  int err;

  /* parse fields */
  for (token = strtok(s, Y4M_DELIM); 
       token != NULL; 
       token = strtok(NULL, Y4M_DELIM)) {
    if (token[0] == '\0') continue;   /* skip empty strings */
    tag = token[0];
    value = token + 1;
    switch (tag) {
    case 'X':  /* 'X' meta-tag */
      if ((err = y4m_xtag_add(&(i->x_tags), token)) != Y4M_OK) return err;
      break;
    default:
      /* possible error on unknown options */
      if (_y4mparam_allow_unknown_tags) {
	/* unknown tags ok:  store in xtag list and warn... */
	if ((err = y4m_xtag_add(&(i->x_tags), token)) != Y4M_OK) return err;
	mp_msg(MSGT_DEMUX, MSGL_WARN, "Unknown frame tag encountered:  '%s'\n", token);
      } else {
	/* unknown tags are *not* ok */
	return Y4M_ERR_BADTAG;
      }
      break;
    }
  }
  /* ta da!  done. */
  return Y4M_OK;
}





/*************************************************************************
 *
 * Read/Write stream header
 *
 *************************************************************************/


int y4m_read_stream_header(stream_t *s, y4m_stream_info_t *i)
{
   char line[Y4M_LINE_MAX];
   char *p;
   int n;
   int err;

   /* read the header line */
   for (n = 0, p = line; n < Y4M_LINE_MAX; n++, p++) {
     if (y4m_read(s, p, 1)) 
       return Y4M_ERR_SYSTEM;
     if (*p == '\n') {
       *p = '\0';           /* Replace linefeed by end of string */
       break;
     }
   }
   if (n >= Y4M_LINE_MAX)
      return Y4M_ERR_HEADER;
   /* look for keyword in header */
   if (strncmp(line, Y4M_MAGIC, strlen(Y4M_MAGIC)))
    return Y4M_ERR_MAGIC;
   if ((err = y4m_parse_stream_tags(line + strlen(Y4M_MAGIC), i)) != Y4M_OK)
     return err;

   i->framelength = (i->height * i->width) * 3 / 2;
   return Y4M_OK;
}


#if 0
int y4m_write_stream_header(int fd, y4m_stream_info_t *i)
{
  char s[Y4M_LINE_MAX+1];
  int n;
  int err;

  y4m_ratio_reduce(&(i->framerate));
  y4m_ratio_reduce(&(i->sampleaspect));
  n = snprintf(s, sizeof(s), "%s W%d H%d F%d:%d I%s A%d:%d",
	       Y4M_MAGIC,
	       i->width,
	       i->height,
	       i->framerate.n, i->framerate.d,
	       (i->interlace == Y4M_ILACE_NONE) ? "p" :
	       (i->interlace == Y4M_ILACE_TOP_FIRST) ? "t" :
	       (i->interlace == Y4M_ILACE_BOTTOM_FIRST) ? "b" : "?",
	       i->sampleaspect.n, i->sampleaspect.d);
  if ((n < 0) || (n > Y4M_LINE_MAX)) return Y4M_ERR_HEADER;
  if ((err = y4m_snprint_xtags(s + n, sizeof(s) - n - 1, &(i->x_tags))) 
      != Y4M_OK) 
    return err;
  /* non-zero on error */
  return (y4m_write(fd, s, strlen(s)) ? Y4M_ERR_SYSTEM : Y4M_OK);
}
#endif




/*************************************************************************
 *
 * Read/Write frame header
 *
 *************************************************************************/

int y4m_read_frame_header(stream_t *s, y4m_frame_info_t *i)
{
  char line[Y4M_LINE_MAX];
  char *p;
  int n;
  ssize_t remain;
  
  /* This is more clever than read_stream_header...
     Try to read "FRAME\n" all at once, and don't try to parse
     if nothing else is there...
  */
  remain = y4m_read(s, line, sizeof(Y4M_FRAME_MAGIC));
  if (remain != 0)
  {
	  /* A clean EOF should end exactly at a frame-boundary */
	  if( remain == sizeof(Y4M_FRAME_MAGIC) )
		  return Y4M_ERR_EOF;
	  else
		  return Y4M_ERR_SYSTEM;
  }
  if (strncmp(line, Y4M_FRAME_MAGIC, sizeof(Y4M_FRAME_MAGIC)-1))
    return Y4M_ERR_MAGIC;
  if (line[sizeof(Y4M_FRAME_MAGIC)-1] == '\n')
    return Y4M_OK; /* done -- no tags:  that was the end-of-line. */

  if (line[sizeof(Y4M_FRAME_MAGIC)-1] != Y4M_DELIM[0]) {
    return Y4M_ERR_MAGIC; /* wasn't a space -- what was it? */
  }

  /* proceed to get the tags... (overwrite the magic) */
  for (n = 0, p = line; n < Y4M_LINE_MAX; n++, p++) {
    if (y4m_read(s, p, 1))
      return Y4M_ERR_SYSTEM;
    if (*p == '\n') {
      *p = '\0';           /* Replace linefeed by end of string */
      break;
    }
  }
  if (n >= Y4M_LINE_MAX) return Y4M_ERR_HEADER;
  /* non-zero on error */
  return y4m_parse_frame_tags(line, i);
}


#if 0
int y4m_write_frame_header(int fd, y4m_frame_info_t *i)
{
  char s[Y4M_LINE_MAX+1];
  int n;
  int err;
  
  n = snprintf(s, sizeof(s), "%s", Y4M_FRAME_MAGIC);
  if ((n < 0) || (n > Y4M_LINE_MAX)) return Y4M_ERR_HEADER;
  if ((err = y4m_snprint_xtags(s + n, sizeof(s) - n - 1, &(i->x_tags))) 
      != Y4M_OK) 
    return err;
  /* non-zero on error */
  return (y4m_write(fd, s, strlen(s)) ? Y4M_ERR_SYSTEM : Y4M_OK);
}
#endif



/*************************************************************************
 *
 * Read/Write entire frame
 *
 *************************************************************************/

int y4m_read_frame(stream_t *s, y4m_stream_info_t *si, 
		   y4m_frame_info_t *fi, unsigned char *yuv[3])
{
  int err;
  int w = si->width;
  int h = si->height;
  
  /* Read frame header */
  if ((err = y4m_read_frame_header(s, fi)) != Y4M_OK) return err;
  /* Read luminance scanlines */
  if (y4m_read(s, yuv[0], w*h)) return Y4M_ERR_SYSTEM;
  /* Read chrominance scanlines */
  if (y4m_read(s, yuv[1], w*h/4)) return Y4M_ERR_SYSTEM;
  if (y4m_read(s, yuv[2], w*h/4)) return Y4M_ERR_SYSTEM;

  return Y4M_OK;
}



#if 0
int y4m_write_frame(int fd, y4m_stream_info_t *si, 
		    y4m_frame_info_t *fi, unsigned char *yuv[3])
{
  int err;
  int w = si->width;
  int h = si->height;

  /* Write frame header */
  if ((err = y4m_write_frame_header(fd, fi)) != Y4M_OK) return err;
  /* Write luminance,chrominance scanlines */
  if (y4m_write(fd, yuv[0], w*h) ||
      y4m_write(fd, yuv[1], w*h/4) ||
      y4m_write(fd, yuv[2], w*h/4))
    return Y4M_ERR_SYSTEM;
  return Y4M_OK;
}
#endif


/*************************************************************************
 *
 * Read/Write entire frame, (de)interleaved (to)from two separate fields
 *
 *************************************************************************/

#if 0
int y4m_read_fields(int fd, y4m_stream_info_t *si, y4m_frame_info_t *fi,
                    unsigned char *upper_field[3], 
                    unsigned char *lower_field[3])
{
  int i, y, err;
  int width = si->width;
  int height = si->height;
  
  /* Read frame header */
  if ((err = y4m_read_frame_header(fd, fi)) != Y4M_OK) return err;
  /* Read Y', Cb, and Cr planes */
  for (i = 0; i < 3; i++) {
    unsigned char *srctop = upper_field[i];
    unsigned char *srcbot = lower_field[i];
    /* alternately write one line from each */
    for (y = 0; y < height; y += 2) {
      if (y4m_read(fd, srctop, width)) return Y4M_ERR_SYSTEM;
      srctop += width;
      if (y4m_read(fd, srcbot, width)) return Y4M_ERR_SYSTEM;
      srcbot += width;
    }
    /* for chroma, width/height are half as big */
    if (i == 0) {
      width /= 2;
      height /= 2;
    }
  }
  return Y4M_OK;
}



int y4m_write_fields(int fd, y4m_stream_info_t *si, y4m_frame_info_t *fi,
                     unsigned char *upper_field[3], 
                     unsigned char *lower_field[3])
{
  int i, y, err;
  int width = si->width;
  int height = si->height;

  /* Write frame header */
  if ((err = y4m_write_frame_header(fd, fi)) != Y4M_OK) return err;
  /* Write Y', Cb, and Cr planes */
  for (i = 0; i < 3; i++) {
    unsigned char *srctop = upper_field[i];
    unsigned char *srcbot = lower_field[i];
    /* alternately write one line from each */
    for (y = 0; y < height; y += 2) {
      if (y4m_write(fd, srctop, width)) return Y4M_ERR_SYSTEM;
      srctop += width;
      if (y4m_write(fd, srcbot, width)) return Y4M_ERR_SYSTEM;
      srcbot += width;
    }
    /* for chroma, width/height are half as big */
    if (i == 0) {
      width /= 2;
      height /= 2;
    }
  }
  return Y4M_OK;
}
#endif


/*************************************************************************
 *
 * Handy logging of stream info
 *
 *************************************************************************/

void y4m_log_stream_info(const char *prefix, y4m_stream_info_t *i)
{
  char s[256];

  snprintf(s, sizeof(s), "  frame size:  ");
  if (i->width == Y4M_UNKNOWN)
    snprintf(s+strlen(s), sizeof(s)-strlen(s), "(?)x");
  else
    snprintf(s+strlen(s), sizeof(s)-strlen(s), "%dx", i->width);
  if (i->height == Y4M_UNKNOWN)
    snprintf(s+strlen(s), sizeof(s)-strlen(s), "(?) pixels ");
  else
    snprintf(s+strlen(s), sizeof(s)-strlen(s), "%d pixels ", i->height);
  if (i->framelength == Y4M_UNKNOWN)
    snprintf(s+strlen(s), sizeof(s)-strlen(s), "(? bytes)");
  else
    snprintf(s+strlen(s), sizeof(s)-strlen(s), "(%d bytes)", i->framelength);
  mp_msg(MSGT_DEMUX, MSGL_V, "%s%s\n", prefix, s);
  if ((i->framerate.n == 0) && (i->framerate.d == 0))
    mp_msg(MSGT_DEMUX, MSGL_V, "%s  frame rate:  ??? fps\n", prefix);
  else
    mp_msg(MSGT_DEMUX, MSGL_V, "%s  frame rate:  %d/%d fps (~%f)\n", prefix,
	      i->framerate.n, i->framerate.d, 
	      (double) i->framerate.n / (double) i->framerate.d);
  mp_msg(MSGT_DEMUX, MSGL_V, "%s   interlace:  %s\n", prefix,
	  (i->interlace == Y4M_ILACE_NONE) ? "none/progressive" :
	  (i->interlace == Y4M_ILACE_TOP_FIRST) ? "top-field-first" :
	  (i->interlace == Y4M_ILACE_BOTTOM_FIRST) ? "bottom-field-first" :
	  "anyone's guess");
  if ((i->sampleaspect.n == 0) && (i->sampleaspect.d == 0))
    mp_msg(MSGT_DEMUX, MSGL_V, "%ssample aspect ratio:  ?:?\n", prefix);
  else
    mp_msg(MSGT_DEMUX, MSGL_V, "%ssample aspect ratio:  %d:%d\n", prefix,
	      i->sampleaspect.n, i->sampleaspect.d);
}


/*************************************************************************
 *
 * Convert error code to string
 *
 *************************************************************************/

const char *y4m_strerr(int err)
{
  switch (err) {
  case Y4M_OK:          return "no error";
  case Y4M_ERR_RANGE:   return "parameter out of range";
  case Y4M_ERR_SYSTEM:  return "stream ended unexpectedly (failed read/write)";
  case Y4M_ERR_HEADER:  return "bad stream or frame header";
  case Y4M_ERR_BADTAG:  return "unknown header tag";
  case Y4M_ERR_MAGIC:   return "bad header magic";
  case Y4M_ERR_XXTAGS:  return "too many xtags";
  case Y4M_ERR_EOF:     return "end-of-file";
  default: 
    return "unknown error code";
  }
}