gstreamer/ext/mplex/yuv4mpeg.cc

/*
 *  yuv4mpeg.c:  Functions for reading and writing "new" YUV4MPEG streams
 *
 *  Copyright (C) 2001 Matthew J. Marjanovic <maddog@mir.com>
 *
 *
 *  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., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 *
 */

#include <config.h>

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "yuv4mpeg.h"
#include "yuv4mpeg_intern.h"
#include "mjpeg_logging.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 (int fd, void *buf, size_t len)
{
  ssize_t n;
  uint8_t *ptr = (uint8_t *) buf;

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


ssize_t
y4m_write (int fd, const void *buf, size_t len)
{
  ssize_t n;
  const uint8_t *ptr = (const uint8_t *) buf;

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



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


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


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;
}



static int
y4m_snprint_xtags (char *s, int maxn, const 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;
}


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, const 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;
  dest->framelength = src->framelength;
  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 (const 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 (const 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 (const 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 (const 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 (const y4m_stream_info_t * si)
{
  return si->sampleaspect;
}

int
y4m_si_get_framelength (const 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, const 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;
	  mjpeg_warn ("Unknown stream tag encountered:  '%s'", 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;
	  mjpeg_warn ("Unknown frame tag encountered:  '%s'", 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 (int fd, 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 (read (fd, p, 1) < 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;
}



int
y4m_write_stream_header (int fd, const y4m_stream_info_t * i)
{
  char s[Y4M_LINE_MAX + 1];
  int n;
  int err;
  y4m_ratio_t rate = i->framerate;
  y4m_ratio_t aspect = i->sampleaspect;

  y4m_ratio_reduce (&rate);
  y4m_ratio_reduce (&aspect);
  n = snprintf (s, sizeof (s), "%s W%d H%d F%d:%d I%s A%d:%d",
		Y4M_MAGIC,
		i->width,
		i->height,
		rate.n, rate.d,
		(i->interlace == Y4M_ILACE_NONE) ? "p" :
		(i->interlace == Y4M_ILACE_TOP_FIRST) ? "t" :
		(i->interlace == Y4M_ILACE_BOTTOM_FIRST) ? "b" : "?", aspect.n, aspect.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);
}





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

int
y4m_read_frame_header (int fd, 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 (fd, line, sizeof (Y4M_FRAME_MAGIC) - 1 + 1);	/* -'\0', +'\n' */
  if (remain < 0)
    return Y4M_ERR_SYSTEM;
  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_BADEOF;
  }
  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 (fd, 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);
}


int
y4m_write_frame_header (int fd, const 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);
}



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

int
y4m_read_frame (int fd, const y4m_stream_info_t * si, y4m_frame_info_t * fi, uint8_t * const yuv[3])
{
  int err;
  int w = si->width;
  int h = si->height;

  /* Read frame header */
  if ((err = y4m_read_frame_header (fd, fi)) != Y4M_OK)
    return err;
  /* Read luminance scanlines */
  if (y4m_read (fd, yuv[0], w * h))
    return Y4M_ERR_SYSTEM;
  /* Read chrominance scanlines */
  if (y4m_read (fd, yuv[1], w * h / 4))
    return Y4M_ERR_SYSTEM;
  if (y4m_read (fd, yuv[2], w * h / 4))
    return Y4M_ERR_SYSTEM;

  return Y4M_OK;
}




int
y4m_write_frame (int fd, const y4m_stream_info_t * si,
		 const y4m_frame_info_t * fi, uint8_t * const 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;
}



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


int
y4m_read_fields (int fd, const y4m_stream_info_t * si, y4m_frame_info_t * fi,
		 uint8_t * const upper_field[3], uint8_t * const 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++) {
    uint8_t *srctop = upper_field[i];
    uint8_t *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, const y4m_stream_info_t * si,
		  const y4m_frame_info_t * fi,
		  uint8_t * const upper_field[3], uint8_t * const 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++) {
    uint8_t *srctop = upper_field[i];
    uint8_t *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;
}



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

void
y4m_log_stream_info (log_level_t level, const char *prefix, const 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);
  mjpeg_log (level, "%s%s", prefix, s);
  if ((i->framerate.n == 0) && (i->framerate.d == 0))
    mjpeg_log (level, "%s  frame rate:  ??? fps", prefix);
  else
    mjpeg_log (level, "%s  frame rate:  %d/%d fps (~%f)", prefix,
	       i->framerate.n, i->framerate.d, (double) i->framerate.n / (double) i->framerate.d);
  mjpeg_log (level, "%s   interlace:  %s", 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))
    mjpeg_log (level, "%ssample aspect ratio:  ?:?", prefix);
  else
    mjpeg_log (level, "%ssample aspect ratio:  %d:%d", 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 "system error (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";
    case Y4M_ERR_BADEOF:
      return "stream ended unexpectedly (EOF)";
    default:
      return "unknown error code";
  }
}