[libvpx] Update to v1.12.0

libs/libvpx/y4minput.c

@@ -10,6 +10,7 @@
  *  Based on code from the OggTheora software codec source code,
  *  Copyright (C) 2002-2010 The Xiph.Org Foundation and contributors.
  */
+#include <assert.h>
 #include <errno.h>
 #include <stdlib.h>
 #include <string.h>
@@ -51,15 +52,8 @@ static int file_read(void *buf, size_t size, FILE *file) {
 }
 
 static int y4m_parse_tags(y4m_input *_y4m, char *_tags) {
-  int got_w;
-  int got_h;
-  int got_fps;
-  int got_interlace;
-  int got_par;
-  int got_chroma;
   char *p;
   char *q;
-  got_w = got_h = got_fps = got_interlace = got_par = got_chroma = 0;
   for (p = _tags;; p = q) {
     /*Skip any leading spaces.*/
     while (*p == ' ') p++;
@@ -72,52 +66,119 @@ static int y4m_parse_tags(y4m_input *_y4m, char *_tags) {
     switch (p[0]) {
       case 'W': {
         if (sscanf(p + 1, "%d", &_y4m->pic_w) != 1) return -1;
-        got_w = 1;
         break;
       }
       case 'H': {
         if (sscanf(p + 1, "%d", &_y4m->pic_h) != 1) return -1;
-        got_h = 1;
         break;
       }
       case 'F': {
         if (sscanf(p + 1, "%d:%d", &_y4m->fps_n, &_y4m->fps_d) != 2) {
           return -1;
         }
-        got_fps = 1;
         break;
       }
       case 'I': {
         _y4m->interlace = p[1];
-        got_interlace = 1;
         break;
       }
       case 'A': {
         if (sscanf(p + 1, "%d:%d", &_y4m->par_n, &_y4m->par_d) != 2) {
           return -1;
         }
-        got_par = 1;
         break;
       }
       case 'C': {
         if (q - p > 16) return -1;
         memcpy(_y4m->chroma_type, p + 1, q - p - 1);
         _y4m->chroma_type[q - p - 1] = '\0';
-        got_chroma = 1;
         break;
       }
         /*Ignore unknown tags.*/
     }
   }
-  if (!got_w || !got_h || !got_fps) return -1;
-  if (!got_interlace) _y4m->interlace = '?';
-  if (!got_par) _y4m->par_n = _y4m->par_d = 0;
-  /*Chroma-type is not specified in older files, e.g., those generated by
-     mplayer.*/
-  if (!got_chroma) strcpy(_y4m->chroma_type, "420");
   return 0;
 }
 
+// Copy a single tag into the buffer, along with a null character.
+// Returns 0 if any file IO errors occur.
+static int copy_tag(char *buf, size_t buf_len, char *end_tag, FILE *file) {
+  size_t i;
+  assert(buf_len >= 1);
+  // Skip leading space characters.
+  do {
+    if (!file_read(buf, 1, file)) {
+      return 0;
+    }
+  } while (buf[0] == ' ');
+
+  // If we hit the newline, treat this as the "empty" tag.
+  if (buf[0] == '\n') {
+    buf[0] = '\0';
+    *end_tag = '\n';
+    return 1;
+  }
+
+  // Copy over characters until a space is hit, or the buffer is exhausted.
+  for (i = 1; i < buf_len; ++i) {
+    if (!file_read(buf + i, 1, file)) {
+      return 0;
+    }
+    if (buf[i] == ' ' || buf[i] == '\n') {
+      break;
+    }
+  }
+  if (i == buf_len) {
+    fprintf(stderr, "Error: Y4M header tags must be less than %lu characters\n",
+            (unsigned long)i);
+    return 0;
+  }
+  *end_tag = buf[i];
+  buf[i] = '\0';
+  return 1;
+}
+
+/* Returns 1 if tags were parsed successfully, 0 otherwise. */
+static int parse_tags(y4m_input *y4m_ctx, FILE *file) {
+  char tag[256];
+  char end; /* Character denoting the end of the tag, ' ' or '\n'. */
+  /* Set Y4M tags to defaults, updating them as processing occurs. Mandatory
+     fields are marked with -1 and will be checked after the tags are parsed. */
+  y4m_ctx->pic_w = -1;
+  y4m_ctx->pic_h = -1;
+  y4m_ctx->fps_n = -1; /* Also serves as marker for fps_d */
+  y4m_ctx->par_n = 0;
+  y4m_ctx->par_d = 0;
+  y4m_ctx->interlace = '?';
+  snprintf(y4m_ctx->chroma_type, sizeof(y4m_ctx->chroma_type), "420");
+
+  /* Find one tag at a time. */
+  do {
+    if (!copy_tag(tag, sizeof(tag), &end, file)) {
+      return 0;
+    }
+    /* y4m_parse_tags returns 0 on success. */
+    if (y4m_parse_tags(y4m_ctx, tag)) {
+      return 0;
+    }
+  } while (end != '\n');
+
+  /* Check the mandatory fields. */
+  if (y4m_ctx->pic_w == -1) {
+    fprintf(stderr, "Width field missing\n");
+    return 0;
+  }
+  if (y4m_ctx->pic_h == -1) {
+    fprintf(stderr, "Height field missing\n");
+    return 0;
+  }
+  if (y4m_ctx->fps_n == -1) {
+    fprintf(stderr, "FPS field missing\n");
+    return 0;
+  }
+  return 1;
+}
+
 /*All anti-aliasing filters in the following conversion functions are based on
    one of two window functions:
   The 6-tap Lanczos window (for down-sampling and shifts):
@@ -224,26 +285,6 @@ static void y4m_42xmpeg2_42xjpeg_helper(unsigned char *_dst,
   }
 }
 
-/*Handles both 422 and 420mpeg2 to 422jpeg and 420jpeg, respectively.*/
-static void y4m_convert_42xmpeg2_42xjpeg(y4m_input *_y4m, unsigned char *_dst,
-                                         unsigned char *_aux) {
-  int c_w;
-  int c_h;
-  int c_sz;
-  int pli;
-  /*Skip past the luma data.*/
-  _dst += _y4m->pic_w * _y4m->pic_h;
-  /*Compute the size of each chroma plane.*/
-  c_w = (_y4m->pic_w + _y4m->dst_c_dec_h - 1) / _y4m->dst_c_dec_h;
-  c_h = (_y4m->pic_h + _y4m->dst_c_dec_v - 1) / _y4m->dst_c_dec_v;
-  c_sz = c_w * c_h;
-  for (pli = 1; pli < 3; pli++) {
-    y4m_42xmpeg2_42xjpeg_helper(_dst, _aux, c_w, c_h);
-    _dst += c_sz;
-    _aux += c_sz;
-  }
-}
-
 /*This format is only used for interlaced content, but is included for
    completeness.
 
@@ -784,301 +825,277 @@ static void y4m_convert_null(y4m_input *_y4m, unsigned char *_dst,
   (void)_aux;
 }
 
-int y4m_input_open(y4m_input *_y4m, FILE *_fin, char *_skip, int _nskip,
-                   int only_420) {
-  char buffer[80] = { 0 };
-  int ret;
-  int i;
-  /*Read until newline, or 80 cols, whichever happens first.*/
-  for (i = 0; i < 79; i++) {
-    if (_nskip > 0) {
-      buffer[i] = *_skip++;
-      _nskip--;
-    } else {
-      if (!file_read(buffer + i, 1, _fin)) return -1;
-    }
-    if (buffer[i] == '\n') break;
+static const char TAG[] = "YUV4MPEG2";
+
+int y4m_input_open(y4m_input *y4m_ctx, FILE *file, char *skip_buffer,
+                   int num_skip, int only_420) {
+  // File must start with |TAG|.
+  char tag_buffer[9];  // 9 == strlen(TAG)
+  // Read as much as possible from |skip_buffer|, which were characters
+  // that were previously read from the file to do input-type detection.
+  assert(num_skip >= 0 && num_skip <= 8);
+  if (num_skip > 0) {
+    memcpy(tag_buffer, skip_buffer, num_skip);
   }
-  /*We skipped too much header data.*/
-  if (_nskip > 0) return -1;
-  if (i == 79) {
-    fprintf(stderr, "Error parsing header; not a YUV2MPEG2 file?\n");
+  // Start reading from the file now that the |skip_buffer| is depleted.
+  if (!file_read(tag_buffer + num_skip, 9 - num_skip, file)) {
     return -1;
   }
-  buffer[i] = '\0';
-  if (memcmp(buffer, "YUV4MPEG", 8)) {
-    fprintf(stderr, "Incomplete magic for YUV4MPEG file.\n");
+  if (memcmp(TAG, tag_buffer, 9) != 0) {
+    fprintf(stderr, "Error parsing header: must start with %s\n", TAG);
     return -1;
   }
-  if (buffer[8] != '2') {
-    fprintf(stderr, "Incorrect YUV input file version; YUV4MPEG2 required.\n");
+  // Next character must be a space.
+  if (!file_read(tag_buffer, 1, file) || tag_buffer[0] != ' ') {
+    fprintf(stderr, "Error parsing header: space must follow %s\n", TAG);
+    return -1;
   }
-  ret = y4m_parse_tags(_y4m, buffer + 5);
-  if (ret < 0) {
-    fprintf(stderr, "Error parsing YUV4MPEG2 header.\n");
-    return ret;
+  if (!parse_tags(y4m_ctx, file)) {
+    fprintf(stderr, "Error parsing %s header.\n", TAG);
   }
-  if (_y4m->interlace == '?') {
+  if (y4m_ctx->interlace == '?') {
     fprintf(stderr,
             "Warning: Input video interlacing format unknown; "
             "assuming progressive scan.\n");
-  } else if (_y4m->interlace != 'p') {
+  } else if (y4m_ctx->interlace != 'p') {
     fprintf(stderr,
             "Input video is interlaced; "
             "Only progressive scan handled.\n");
     return -1;
   }
-  _y4m->vpx_fmt = VPX_IMG_FMT_I420;
-  _y4m->bps = 12;
-  _y4m->bit_depth = 8;
-  if (strcmp(_y4m->chroma_type, "420") == 0 ||
-      strcmp(_y4m->chroma_type, "420jpeg") == 0) {
-    _y4m->src_c_dec_h = _y4m->dst_c_dec_h = _y4m->src_c_dec_v =
-        _y4m->dst_c_dec_v = 2;
-    _y4m->dst_buf_read_sz =
-        _y4m->pic_w * _y4m->pic_h +
-        2 * ((_y4m->pic_w + 1) / 2) * ((_y4m->pic_h + 1) / 2);
+  y4m_ctx->vpx_fmt = VPX_IMG_FMT_I420;
+  y4m_ctx->bps = 12;
+  y4m_ctx->bit_depth = 8;
+  y4m_ctx->aux_buf = NULL;
+  y4m_ctx->dst_buf = NULL;
+  if (strcmp(y4m_ctx->chroma_type, "420") == 0 ||
+      strcmp(y4m_ctx->chroma_type, "420jpeg") == 0 ||
+      strcmp(y4m_ctx->chroma_type, "420mpeg2") == 0) {
+    y4m_ctx->src_c_dec_h = y4m_ctx->dst_c_dec_h = y4m_ctx->src_c_dec_v =
+        y4m_ctx->dst_c_dec_v = 2;
+    y4m_ctx->dst_buf_read_sz =
+        y4m_ctx->pic_w * y4m_ctx->pic_h +
+        2 * ((y4m_ctx->pic_w + 1) / 2) * ((y4m_ctx->pic_h + 1) / 2);
     /* Natively supported: no conversion required. */
-    _y4m->aux_buf_sz = _y4m->aux_buf_read_sz = 0;
-    _y4m->convert = y4m_convert_null;
-  } else if (strcmp(_y4m->chroma_type, "420p10") == 0) {
-    _y4m->src_c_dec_h = 2;
-    _y4m->dst_c_dec_h = 2;
-    _y4m->src_c_dec_v = 2;
-    _y4m->dst_c_dec_v = 2;
-    _y4m->dst_buf_read_sz =
-        2 * (_y4m->pic_w * _y4m->pic_h +
-             2 * ((_y4m->pic_w + 1) / 2) * ((_y4m->pic_h + 1) / 2));
+    y4m_ctx->aux_buf_sz = y4m_ctx->aux_buf_read_sz = 0;
+    y4m_ctx->convert = y4m_convert_null;
+  } else if (strcmp(y4m_ctx->chroma_type, "420p10") == 0) {
+    y4m_ctx->src_c_dec_h = 2;
+    y4m_ctx->dst_c_dec_h = 2;
+    y4m_ctx->src_c_dec_v = 2;
+    y4m_ctx->dst_c_dec_v = 2;
+    y4m_ctx->dst_buf_read_sz =
+        2 * (y4m_ctx->pic_w * y4m_ctx->pic_h +
+             2 * ((y4m_ctx->pic_w + 1) / 2) * ((y4m_ctx->pic_h + 1) / 2));
     /* Natively supported: no conversion required. */
-    _y4m->aux_buf_sz = _y4m->aux_buf_read_sz = 0;
-    _y4m->convert = y4m_convert_null;
-    _y4m->bit_depth = 10;
-    _y4m->bps = 15;
-    _y4m->vpx_fmt = VPX_IMG_FMT_I42016;
+    y4m_ctx->aux_buf_sz = y4m_ctx->aux_buf_read_sz = 0;
+    y4m_ctx->convert = y4m_convert_null;
+    y4m_ctx->bit_depth = 10;
+    y4m_ctx->bps = 15;
+    y4m_ctx->vpx_fmt = VPX_IMG_FMT_I42016;
     if (only_420) {
       fprintf(stderr, "Unsupported conversion from 420p10 to 420jpeg\n");
       return -1;
     }
-  } else if (strcmp(_y4m->chroma_type, "420p12") == 0) {
-    _y4m->src_c_dec_h = 2;
-    _y4m->dst_c_dec_h = 2;
-    _y4m->src_c_dec_v = 2;
-    _y4m->dst_c_dec_v = 2;
-    _y4m->dst_buf_read_sz =
-        2 * (_y4m->pic_w * _y4m->pic_h +
-             2 * ((_y4m->pic_w + 1) / 2) * ((_y4m->pic_h + 1) / 2));
+  } else if (strcmp(y4m_ctx->chroma_type, "420p12") == 0) {
+    y4m_ctx->src_c_dec_h = 2;
+    y4m_ctx->dst_c_dec_h = 2;
+    y4m_ctx->src_c_dec_v = 2;
+    y4m_ctx->dst_c_dec_v = 2;
+    y4m_ctx->dst_buf_read_sz =
+        2 * (y4m_ctx->pic_w * y4m_ctx->pic_h +
+             2 * ((y4m_ctx->pic_w + 1) / 2) * ((y4m_ctx->pic_h + 1) / 2));
     /* Natively supported: no conversion required. */
-    _y4m->aux_buf_sz = _y4m->aux_buf_read_sz = 0;
-    _y4m->convert = y4m_convert_null;
-    _y4m->bit_depth = 12;
-    _y4m->bps = 18;
-    _y4m->vpx_fmt = VPX_IMG_FMT_I42016;
+    y4m_ctx->aux_buf_sz = y4m_ctx->aux_buf_read_sz = 0;
+    y4m_ctx->convert = y4m_convert_null;
+    y4m_ctx->bit_depth = 12;
+    y4m_ctx->bps = 18;
+    y4m_ctx->vpx_fmt = VPX_IMG_FMT_I42016;
     if (only_420) {
       fprintf(stderr, "Unsupported conversion from 420p12 to 420jpeg\n");
       return -1;
     }
-  } else if (strcmp(_y4m->chroma_type, "420mpeg2") == 0) {
-    _y4m->src_c_dec_h = _y4m->dst_c_dec_h = _y4m->src_c_dec_v =
-        _y4m->dst_c_dec_v = 2;
-    _y4m->dst_buf_read_sz = _y4m->pic_w * _y4m->pic_h;
-    /*Chroma filter required: read into the aux buf first.*/
-    _y4m->aux_buf_sz = _y4m->aux_buf_read_sz =
-        2 * ((_y4m->pic_w + 1) / 2) * ((_y4m->pic_h + 1) / 2);
-    _y4m->convert = y4m_convert_42xmpeg2_42xjpeg;
-  } else if (strcmp(_y4m->chroma_type, "420paldv") == 0) {
-    _y4m->src_c_dec_h = _y4m->dst_c_dec_h = _y4m->src_c_dec_v =
-        _y4m->dst_c_dec_v = 2;
-    _y4m->dst_buf_read_sz = _y4m->pic_w * _y4m->pic_h;
+  } else if (strcmp(y4m_ctx->chroma_type, "420paldv") == 0) {
+    y4m_ctx->src_c_dec_h = y4m_ctx->dst_c_dec_h = y4m_ctx->src_c_dec_v =
+        y4m_ctx->dst_c_dec_v = 2;
+    y4m_ctx->dst_buf_read_sz = y4m_ctx->pic_w * y4m_ctx->pic_h;
     /*Chroma filter required: read into the aux buf first.
       We need to make two filter passes, so we need some extra space in the
        aux buffer.*/
-    _y4m->aux_buf_sz = 3 * ((_y4m->pic_w + 1) / 2) * ((_y4m->pic_h + 1) / 2);
-    _y4m->aux_buf_read_sz =
-        2 * ((_y4m->pic_w + 1) / 2) * ((_y4m->pic_h + 1) / 2);
-    _y4m->convert = y4m_convert_42xpaldv_42xjpeg;
-  } else if (strcmp(_y4m->chroma_type, "422jpeg") == 0) {
-    _y4m->src_c_dec_h = _y4m->dst_c_dec_h = 2;
-    _y4m->src_c_dec_v = 1;
-    _y4m->dst_c_dec_v = 2;
-    _y4m->dst_buf_read_sz = _y4m->pic_w * _y4m->pic_h;
+    y4m_ctx->aux_buf_sz =
+        3 * ((y4m_ctx->pic_w + 1) / 2) * ((y4m_ctx->pic_h + 1) / 2);
+    y4m_ctx->aux_buf_read_sz =
+        2 * ((y4m_ctx->pic_w + 1) / 2) * ((y4m_ctx->pic_h + 1) / 2);
+    y4m_ctx->convert = y4m_convert_42xpaldv_42xjpeg;
+  } else if (strcmp(y4m_ctx->chroma_type, "422jpeg") == 0) {
+    y4m_ctx->src_c_dec_h = y4m_ctx->dst_c_dec_h = 2;
+    y4m_ctx->src_c_dec_v = 1;
+    y4m_ctx->dst_c_dec_v = 2;
+    y4m_ctx->dst_buf_read_sz = y4m_ctx->pic_w * y4m_ctx->pic_h;
     /*Chroma filter required: read into the aux buf first.*/
-    _y4m->aux_buf_sz = _y4m->aux_buf_read_sz =
-        2 * ((_y4m->pic_w + 1) / 2) * _y4m->pic_h;
-    _y4m->convert = y4m_convert_422jpeg_420jpeg;
-  } else if (strcmp(_y4m->chroma_type, "422") == 0) {
-    _y4m->src_c_dec_h = 2;
-    _y4m->src_c_dec_v = 1;
+    y4m_ctx->aux_buf_sz = y4m_ctx->aux_buf_read_sz =
+        2 * ((y4m_ctx->pic_w + 1) / 2) * y4m_ctx->pic_h;
+    y4m_ctx->convert = y4m_convert_422jpeg_420jpeg;
+  } else if (strcmp(y4m_ctx->chroma_type, "422") == 0) {
+    y4m_ctx->src_c_dec_h = 2;
+    y4m_ctx->src_c_dec_v = 1;
     if (only_420) {
-      _y4m->dst_c_dec_h = 2;
-      _y4m->dst_c_dec_v = 2;
-      _y4m->dst_buf_read_sz = _y4m->pic_w * _y4m->pic_h;
+      y4m_ctx->dst_c_dec_h = 2;
+      y4m_ctx->dst_c_dec_v = 2;
+      y4m_ctx->dst_buf_read_sz = y4m_ctx->pic_w * y4m_ctx->pic_h;
       /*Chroma filter required: read into the aux buf first.
         We need to make two filter passes, so we need some extra space in the
          aux buffer.*/
-      _y4m->aux_buf_read_sz = 2 * ((_y4m->pic_w + 1) / 2) * _y4m->pic_h;
-      _y4m->aux_buf_sz =
-          _y4m->aux_buf_read_sz + ((_y4m->pic_w + 1) / 2) * _y4m->pic_h;
-      _y4m->convert = y4m_convert_422_420jpeg;
+      y4m_ctx->aux_buf_read_sz =
+          2 * ((y4m_ctx->pic_w + 1) / 2) * y4m_ctx->pic_h;
+      y4m_ctx->aux_buf_sz = y4m_ctx->aux_buf_read_sz +
+                            ((y4m_ctx->pic_w + 1) / 2) * y4m_ctx->pic_h;
+      y4m_ctx->convert = y4m_convert_422_420jpeg;
     } else {
-      _y4m->vpx_fmt = VPX_IMG_FMT_I422;
-      _y4m->bps = 16;
-      _y4m->dst_c_dec_h = _y4m->src_c_dec_h;
-      _y4m->dst_c_dec_v = _y4m->src_c_dec_v;
-      _y4m->dst_buf_read_sz =
-          _y4m->pic_w * _y4m->pic_h + 2 * ((_y4m->pic_w + 1) / 2) * _y4m->pic_h;
+      y4m_ctx->vpx_fmt = VPX_IMG_FMT_I422;
+      y4m_ctx->bps = 16;
+      y4m_ctx->dst_c_dec_h = y4m_ctx->src_c_dec_h;
+      y4m_ctx->dst_c_dec_v = y4m_ctx->src_c_dec_v;
+      y4m_ctx->dst_buf_read_sz =
+          y4m_ctx->pic_w * y4m_ctx->pic_h +
+          2 * ((y4m_ctx->pic_w + 1) / 2) * y4m_ctx->pic_h;
       /*Natively supported: no conversion required.*/
-      _y4m->aux_buf_sz = _y4m->aux_buf_read_sz = 0;
-      _y4m->convert = y4m_convert_null;
+      y4m_ctx->aux_buf_sz = y4m_ctx->aux_buf_read_sz = 0;
+      y4m_ctx->convert = y4m_convert_null;
     }
-  } else if (strcmp(_y4m->chroma_type, "422p10") == 0) {
-    _y4m->src_c_dec_h = 2;
-    _y4m->src_c_dec_v = 1;
-    _y4m->vpx_fmt = VPX_IMG_FMT_I42216;
-    _y4m->bps = 20;
-    _y4m->bit_depth = 10;
-    _y4m->dst_c_dec_h = _y4m->src_c_dec_h;
-    _y4m->dst_c_dec_v = _y4m->src_c_dec_v;
-    _y4m->dst_buf_read_sz = 2 * (_y4m->pic_w * _y4m->pic_h +
-                                 2 * ((_y4m->pic_w + 1) / 2) * _y4m->pic_h);
-    _y4m->aux_buf_sz = _y4m->aux_buf_read_sz = 0;
-    _y4m->convert = y4m_convert_null;
+  } else if (strcmp(y4m_ctx->chroma_type, "422p10") == 0) {
+    y4m_ctx->src_c_dec_h = 2;
+    y4m_ctx->src_c_dec_v = 1;
+    y4m_ctx->vpx_fmt = VPX_IMG_FMT_I42216;
+    y4m_ctx->bps = 20;
+    y4m_ctx->bit_depth = 10;
+    y4m_ctx->dst_c_dec_h = y4m_ctx->src_c_dec_h;
+    y4m_ctx->dst_c_dec_v = y4m_ctx->src_c_dec_v;
+    y4m_ctx->dst_buf_read_sz =
+        2 * (y4m_ctx->pic_w * y4m_ctx->pic_h +
+             2 * ((y4m_ctx->pic_w + 1) / 2) * y4m_ctx->pic_h);
+    y4m_ctx->aux_buf_sz = y4m_ctx->aux_buf_read_sz = 0;
+    y4m_ctx->convert = y4m_convert_null;
     if (only_420) {
       fprintf(stderr, "Unsupported conversion from 422p10 to 420jpeg\n");
       return -1;
     }
-  } else if (strcmp(_y4m->chroma_type, "422p12") == 0) {
-    _y4m->src_c_dec_h = 2;
-    _y4m->src_c_dec_v = 1;
-    _y4m->vpx_fmt = VPX_IMG_FMT_I42216;
-    _y4m->bps = 24;
-    _y4m->bit_depth = 12;
-    _y4m->dst_c_dec_h = _y4m->src_c_dec_h;
-    _y4m->dst_c_dec_v = _y4m->src_c_dec_v;
-    _y4m->dst_buf_read_sz = 2 * (_y4m->pic_w * _y4m->pic_h +
-                                 2 * ((_y4m->pic_w + 1) / 2) * _y4m->pic_h);
-    _y4m->aux_buf_sz = _y4m->aux_buf_read_sz = 0;
-    _y4m->convert = y4m_convert_null;
+  } else if (strcmp(y4m_ctx->chroma_type, "422p12") == 0) {
+    y4m_ctx->src_c_dec_h = 2;
+    y4m_ctx->src_c_dec_v = 1;
+    y4m_ctx->vpx_fmt = VPX_IMG_FMT_I42216;
+    y4m_ctx->bps = 24;
+    y4m_ctx->bit_depth = 12;
+    y4m_ctx->dst_c_dec_h = y4m_ctx->src_c_dec_h;
+    y4m_ctx->dst_c_dec_v = y4m_ctx->src_c_dec_v;
+    y4m_ctx->dst_buf_read_sz =
+        2 * (y4m_ctx->pic_w * y4m_ctx->pic_h +
+             2 * ((y4m_ctx->pic_w + 1) / 2) * y4m_ctx->pic_h);
+    y4m_ctx->aux_buf_sz = y4m_ctx->aux_buf_read_sz = 0;
+    y4m_ctx->convert = y4m_convert_null;
     if (only_420) {
       fprintf(stderr, "Unsupported conversion from 422p12 to 420jpeg\n");
       return -1;
     }
-  } else if (strcmp(_y4m->chroma_type, "411") == 0) {
-    _y4m->src_c_dec_h = 4;
-    _y4m->dst_c_dec_h = 2;
-    _y4m->src_c_dec_v = 1;
-    _y4m->dst_c_dec_v = 2;
-    _y4m->dst_buf_read_sz = _y4m->pic_w * _y4m->pic_h;
+  } else if (strcmp(y4m_ctx->chroma_type, "411") == 0) {
+    y4m_ctx->src_c_dec_h = 4;
+    y4m_ctx->dst_c_dec_h = 2;
+    y4m_ctx->src_c_dec_v = 1;
+    y4m_ctx->dst_c_dec_v = 2;
+    y4m_ctx->dst_buf_read_sz = y4m_ctx->pic_w * y4m_ctx->pic_h;
     /*Chroma filter required: read into the aux buf first.
       We need to make two filter passes, so we need some extra space in the
        aux buffer.*/
-    _y4m->aux_buf_read_sz = 2 * ((_y4m->pic_w + 3) / 4) * _y4m->pic_h;
-    _y4m->aux_buf_sz =
-        _y4m->aux_buf_read_sz + ((_y4m->pic_w + 1) / 2) * _y4m->pic_h;
-    _y4m->convert = y4m_convert_411_420jpeg;
+    y4m_ctx->aux_buf_read_sz = 2 * ((y4m_ctx->pic_w + 3) / 4) * y4m_ctx->pic_h;
+    y4m_ctx->aux_buf_sz =
+        y4m_ctx->aux_buf_read_sz + ((y4m_ctx->pic_w + 1) / 2) * y4m_ctx->pic_h;
+    y4m_ctx->convert = y4m_convert_411_420jpeg;
     fprintf(stderr, "Unsupported conversion from yuv 411\n");
     return -1;
-  } else if (strcmp(_y4m->chroma_type, "444") == 0) {
-    _y4m->src_c_dec_h = 1;
-    _y4m->src_c_dec_v = 1;
+  } else if (strcmp(y4m_ctx->chroma_type, "444") == 0) {
+    y4m_ctx->src_c_dec_h = 1;
+    y4m_ctx->src_c_dec_v = 1;
     if (only_420) {
-      _y4m->dst_c_dec_h = 2;
-      _y4m->dst_c_dec_v = 2;
-      _y4m->dst_buf_read_sz = _y4m->pic_w * _y4m->pic_h;
+      y4m_ctx->dst_c_dec_h = 2;
+      y4m_ctx->dst_c_dec_v = 2;
+      y4m_ctx->dst_buf_read_sz = y4m_ctx->pic_w * y4m_ctx->pic_h;
       /*Chroma filter required: read into the aux buf first.
         We need to make two filter passes, so we need some extra space in the
          aux buffer.*/
-      _y4m->aux_buf_read_sz = 2 * _y4m->pic_w * _y4m->pic_h;
-      _y4m->aux_buf_sz =
-          _y4m->aux_buf_read_sz + ((_y4m->pic_w + 1) / 2) * _y4m->pic_h;
-      _y4m->convert = y4m_convert_444_420jpeg;
+      y4m_ctx->aux_buf_read_sz = 2 * y4m_ctx->pic_w * y4m_ctx->pic_h;
+      y4m_ctx->aux_buf_sz = y4m_ctx->aux_buf_read_sz +
+                            ((y4m_ctx->pic_w + 1) / 2) * y4m_ctx->pic_h;
+      y4m_ctx->convert = y4m_convert_444_420jpeg;
     } else {
-      _y4m->vpx_fmt = VPX_IMG_FMT_I444;
-      _y4m->bps = 24;
-      _y4m->dst_c_dec_h = _y4m->src_c_dec_h;
-      _y4m->dst_c_dec_v = _y4m->src_c_dec_v;
-      _y4m->dst_buf_read_sz = 3 * _y4m->pic_w * _y4m->pic_h;
+      y4m_ctx->vpx_fmt = VPX_IMG_FMT_I444;
+      y4m_ctx->bps = 24;
+      y4m_ctx->dst_c_dec_h = y4m_ctx->src_c_dec_h;
+      y4m_ctx->dst_c_dec_v = y4m_ctx->src_c_dec_v;
+      y4m_ctx->dst_buf_read_sz = 3 * y4m_ctx->pic_w * y4m_ctx->pic_h;
       /*Natively supported: no conversion required.*/
-      _y4m->aux_buf_sz = _y4m->aux_buf_read_sz = 0;
-      _y4m->convert = y4m_convert_null;
+      y4m_ctx->aux_buf_sz = y4m_ctx->aux_buf_read_sz = 0;
+      y4m_ctx->convert = y4m_convert_null;
     }
-  } else if (strcmp(_y4m->chroma_type, "444p10") == 0) {
-    _y4m->src_c_dec_h = 1;
-    _y4m->src_c_dec_v = 1;
-    _y4m->vpx_fmt = VPX_IMG_FMT_I44416;
-    _y4m->bps = 30;
-    _y4m->bit_depth = 10;
-    _y4m->dst_c_dec_h = _y4m->src_c_dec_h;
-    _y4m->dst_c_dec_v = _y4m->src_c_dec_v;
-    _y4m->dst_buf_read_sz = 2 * 3 * _y4m->pic_w * _y4m->pic_h;
-    _y4m->aux_buf_sz = _y4m->aux_buf_read_sz = 0;
-    _y4m->convert = y4m_convert_null;
+  } else if (strcmp(y4m_ctx->chroma_type, "444p10") == 0) {
+    y4m_ctx->src_c_dec_h = 1;
+    y4m_ctx->src_c_dec_v = 1;
+    y4m_ctx->vpx_fmt = VPX_IMG_FMT_I44416;
+    y4m_ctx->bps = 30;
+    y4m_ctx->bit_depth = 10;
+    y4m_ctx->dst_c_dec_h = y4m_ctx->src_c_dec_h;
+    y4m_ctx->dst_c_dec_v = y4m_ctx->src_c_dec_v;
+    y4m_ctx->dst_buf_read_sz = 2 * 3 * y4m_ctx->pic_w * y4m_ctx->pic_h;
+    y4m_ctx->aux_buf_sz = y4m_ctx->aux_buf_read_sz = 0;
+    y4m_ctx->convert = y4m_convert_null;
     if (only_420) {
       fprintf(stderr, "Unsupported conversion from 444p10 to 420jpeg\n");
       return -1;
     }
-  } else if (strcmp(_y4m->chroma_type, "444p12") == 0) {
-    _y4m->src_c_dec_h = 1;
-    _y4m->src_c_dec_v = 1;
-    _y4m->vpx_fmt = VPX_IMG_FMT_I44416;
-    _y4m->bps = 36;
-    _y4m->bit_depth = 12;
-    _y4m->dst_c_dec_h = _y4m->src_c_dec_h;
-    _y4m->dst_c_dec_v = _y4m->src_c_dec_v;
-    _y4m->dst_buf_read_sz = 2 * 3 * _y4m->pic_w * _y4m->pic_h;
-    _y4m->aux_buf_sz = _y4m->aux_buf_read_sz = 0;
-    _y4m->convert = y4m_convert_null;
+  } else if (strcmp(y4m_ctx->chroma_type, "444p12") == 0) {
+    y4m_ctx->src_c_dec_h = 1;
+    y4m_ctx->src_c_dec_v = 1;
+    y4m_ctx->vpx_fmt = VPX_IMG_FMT_I44416;
+    y4m_ctx->bps = 36;
+    y4m_ctx->bit_depth = 12;
+    y4m_ctx->dst_c_dec_h = y4m_ctx->src_c_dec_h;
+    y4m_ctx->dst_c_dec_v = y4m_ctx->src_c_dec_v;
+    y4m_ctx->dst_buf_read_sz = 2 * 3 * y4m_ctx->pic_w * y4m_ctx->pic_h;
+    y4m_ctx->aux_buf_sz = y4m_ctx->aux_buf_read_sz = 0;
+    y4m_ctx->convert = y4m_convert_null;
     if (only_420) {
       fprintf(stderr, "Unsupported conversion from 444p12 to 420jpeg\n");
       return -1;
     }
-  } else if (strcmp(_y4m->chroma_type, "444alpha") == 0) {
-    _y4m->src_c_dec_h = 1;
-    _y4m->src_c_dec_v = 1;
-    if (only_420) {
-      _y4m->dst_c_dec_h = 2;
-      _y4m->dst_c_dec_v = 2;
-      _y4m->dst_buf_read_sz = _y4m->pic_w * _y4m->pic_h;
-      /*Chroma filter required: read into the aux buf first.
-        We need to make two filter passes, so we need some extra space in the
-         aux buffer.
-        The extra plane also gets read into the aux buf.
-        It will be discarded.*/
-      _y4m->aux_buf_sz = _y4m->aux_buf_read_sz = 3 * _y4m->pic_w * _y4m->pic_h;
-      _y4m->convert = y4m_convert_444_420jpeg;
-    } else {
-      _y4m->vpx_fmt = VPX_IMG_FMT_444A;
-      _y4m->bps = 32;
-      _y4m->dst_c_dec_h = _y4m->src_c_dec_h;
-      _y4m->dst_c_dec_v = _y4m->src_c_dec_v;
-      _y4m->dst_buf_read_sz = 4 * _y4m->pic_w * _y4m->pic_h;
-      /*Natively supported: no conversion required.*/
-      _y4m->aux_buf_sz = _y4m->aux_buf_read_sz = 0;
-      _y4m->convert = y4m_convert_null;
-    }
-  } else if (strcmp(_y4m->chroma_type, "mono") == 0) {
-    _y4m->src_c_dec_h = _y4m->src_c_dec_v = 0;
-    _y4m->dst_c_dec_h = _y4m->dst_c_dec_v = 2;
-    _y4m->dst_buf_read_sz = _y4m->pic_w * _y4m->pic_h;
+  } else if (strcmp(y4m_ctx->chroma_type, "mono") == 0) {
+    y4m_ctx->src_c_dec_h = y4m_ctx->src_c_dec_v = 0;
+    y4m_ctx->dst_c_dec_h = y4m_ctx->dst_c_dec_v = 2;
+    y4m_ctx->dst_buf_read_sz = y4m_ctx->pic_w * y4m_ctx->pic_h;
     /*No extra space required, but we need to clear the chroma planes.*/
-    _y4m->aux_buf_sz = _y4m->aux_buf_read_sz = 0;
-    _y4m->convert = y4m_convert_mono_420jpeg;
+    y4m_ctx->aux_buf_sz = y4m_ctx->aux_buf_read_sz = 0;
+    y4m_ctx->convert = y4m_convert_mono_420jpeg;
   } else {
-    fprintf(stderr, "Unknown chroma sampling type: %s\n", _y4m->chroma_type);
+    fprintf(stderr, "Unknown chroma sampling type: %s\n", y4m_ctx->chroma_type);
     return -1;
   }
   /*The size of the final frame buffers is always computed from the
      destination chroma decimation type.*/
-  _y4m->dst_buf_sz =
-      _y4m->pic_w * _y4m->pic_h +
-      2 * ((_y4m->pic_w + _y4m->dst_c_dec_h - 1) / _y4m->dst_c_dec_h) *
-          ((_y4m->pic_h + _y4m->dst_c_dec_v - 1) / _y4m->dst_c_dec_v);
-  if (_y4m->bit_depth == 8)
-    _y4m->dst_buf = (unsigned char *)malloc(_y4m->dst_buf_sz);
+  y4m_ctx->dst_buf_sz =
+      y4m_ctx->pic_w * y4m_ctx->pic_h +
+      2 * ((y4m_ctx->pic_w + y4m_ctx->dst_c_dec_h - 1) / y4m_ctx->dst_c_dec_h) *
+          ((y4m_ctx->pic_h + y4m_ctx->dst_c_dec_v - 1) / y4m_ctx->dst_c_dec_v);
+  if (y4m_ctx->bit_depth == 8)
+    y4m_ctx->dst_buf = (unsigned char *)malloc(y4m_ctx->dst_buf_sz);
   else
-    _y4m->dst_buf = (unsigned char *)malloc(2 * _y4m->dst_buf_sz);
+    y4m_ctx->dst_buf = (unsigned char *)malloc(2 * y4m_ctx->dst_buf_sz);
+  if (!y4m_ctx->dst_buf) return -1;
 
-  if (_y4m->aux_buf_sz > 0)
-    _y4m->aux_buf = (unsigned char *)malloc(_y4m->aux_buf_sz);
+  if (y4m_ctx->aux_buf_sz > 0) {
+    y4m_ctx->aux_buf = (unsigned char *)malloc(y4m_ctx->aux_buf_sz);
+    if (!y4m_ctx->aux_buf) {
+      free(y4m_ctx->dst_buf);
+      return -1;
+    }
+  }
   return 0;
 }