subtitles: style support for common SubRip tags and MicroDVD

SubRip subtitles have no "official" spec for any styling support, but
various tags are in common use; previous code filtered out text
between <> to remove HTML-style tags. Add support for those tags and
for MicroDVD subtitle styling. The style display is implemented by
converting the subtitles to the ASS subtitle format and displaying
them with libass, so libass needs to be enabled.

Original patch by Clément Bœsch <ubitux@gmail.com>.

2 files changed, 529 insertions, 0 deletions

diff --git a/sub/subassconvert.c b/sub/subassconvert.c
new file mode 100644
index 0000000000..773cb7f4d7
--- /dev/null
+++ b/sub/subassconvert.c
@@ -0,0 +1,502 @@
+/*
+ * Subtitles converter to SSA/ASS in order to allow special formatting
+ *
+ * This file is part of MPlayer.
+ *
+ * MPlayer 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.
+ *
+ * MPlayer 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 MPlayer; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include <string.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdarg.h>
+#include <stdbool.h>
+
+#include "mp_msg.h"
+#include "subassconvert.h"
+#include "bstr.h"
+#include "libavutil/common.h"
+
+struct line {
+    char *buf;
+    int bufsize;
+    int len;
+};
+
+#ifdef __GNUC__
+static void append_text(struct line *dst, char *fmt, ...) __attribute__ ((format(printf, 2, 3)));
+#endif
+
+static void append_text(struct line *dst, char *fmt, ...)
+{
+    va_list va;
+    va_start(va, fmt);
+    int ret = vsnprintf(dst->buf + dst->len, dst->bufsize - dst->len, fmt, va);
+    if (ret < 0)
+        goto out;
+    dst->len += ret;
+    if (dst->len > dst->bufsize)
+        dst->len = dst->bufsize;
+ out:
+    va_end(va);
+}
+
+static int indexof(const char *s, int c)
+{
+    char *f = strchr(s, c);
+    return f ? (f - s) : -1;
+}
+
+
+
+/*
+ *      SubRip
+ *
+ *      Support basic tags (italic, bold, underline, strike-through)
+ *      and font tag with size, color and face attributes.
+ *
+ */
+
+struct font_tag {
+    int size;
+    uint32_t color;
+    struct bstr face;
+    bool has_size : 1;
+    bool has_color : 1;
+    bool has_face : 1;
+};
+
+static const struct tag_conv {
+    char *from;
+    char *to;
+} subrip_basic_tags[] = {
+    {"<i>", "{\\i1}"}, {"</i>", "{\\i0}"},
+    {"<b>", "{\\b1}"}, {"</b>", "{\\b0}"},
+    {"<u>", "{\\u1}"}, {"</u>", "{\\u0}"},
+    {"<s>", "{\\s1}"}, {"</s>", "{\\s0}"},
+    {"{", "\\{"}, {"}", "\\}"},
+    {"\n", "\\N"}
+};
+
+static const struct {
+    char *s;
+    uint32_t v;
+} subrip_web_colors[] = {
+    /* 16 named HTML colors in BGR format */
+    {"red",     0x0000ff}, {"blue",   0xff0000}, {"lime",   0x00ff00},
+    {"aqua",    0xffff00}, {"purple", 0x800080}, {"yellow", 0x00ffff},
+    {"fuchsia", 0xff00ff}, {"white",  0xffffff}, {"gray",   0x808080},
+    {"maroon",  0x000080}, {"olive",  0x008080}, {"black",  0x000000},
+    {"silver",  0xc0c0c0}, {"teal",   0x808000}, {"green",  0x008000},
+    {"navy",    0x800000}
+};
+
+#define SUBRIP_MAX_STACKED_FONT_TAGS    16
+
+void subassconvert_subrip(const char *orig, char *dest, int dest_buffer_size)
+{
+    /* line is not const to avoid warnings with strtol, etc.
+     * orig content won't be changed */
+    char *line = (char *)orig;
+    struct line new_line = {
+        .buf = dest,
+        .bufsize = dest_buffer_size,
+    };
+    struct font_tag font_stack[SUBRIP_MAX_STACKED_FONT_TAGS + 1];
+    font_stack[0] = (struct font_tag){0}; // type with all defaults
+    int sp = 0;
+
+    while (*line && new_line.len < new_line.bufsize - 1) {
+        char *orig_line = line;
+
+        for (int i = 0; i < FF_ARRAY_ELEMS(subrip_basic_tags); i++) {
+            const struct tag_conv *tag = &subrip_basic_tags[i];
+            int from_len = strlen(tag->from);
+            if (strncmp(line, tag->from, from_len) == 0) {
+                append_text(&new_line, "%s", tag->to);
+                line += from_len;
+            }
+        }
+
+        if (strncmp(line, "</font>", 7) == 0) {
+            /* Closing font tag */
+            line += 7;
+
+            if (sp > 0) {
+                struct font_tag *tag = &font_stack[sp];
+                struct font_tag *last_tag = &tag[-1];
+                sp--;
+
+                if (tag->has_size) {
+                    if (!last_tag->has_size)
+                        append_text(&new_line, "{\\fs}");
+                    else if (last_tag->size != tag->size)
+                        append_text(&new_line, "{\\fs%d}", last_tag->size);
+                }
+
+                if (tag->has_color) {
+                    if (!last_tag->has_color)
+                        append_text(&new_line, "{\\c}");
+                    else if (last_tag->color != tag->color)
+                        append_text(&new_line, "{\\c&H%06X&}", last_tag->color);
+                }
+
+                if (tag->has_face) {
+                    if (!last_tag->has_face)
+                        append_text(&new_line, "{\\fn}");
+                    else if (bstrcmp(last_tag->face, tag->face) != 0)
+                        append_text(&new_line, "{\\fn%.*s}",
+                                    BSTR_P(last_tag->face));
+                }
+            }
+        } else if (strncmp(line, "<font ", 6) == 0
+                   && sp + 1 < FF_ARRAY_ELEMS(font_stack)) {
+            /* Opening font tag */
+            char *potential_font_tag_start = line;
+            int len_backup = new_line.len;
+            struct font_tag *tag = &font_stack[sp + 1];
+            bool has_valid_attr = false;
+
+            *tag = tag[-1]; // keep values from previous tag
+            line += 6;
+
+            while (*line && *line != '>') {
+                if (strncmp(line, "size=\"", 6) == 0) {
+                    line += 6;
+                    tag->size = strtol(line, &line, 10);
+                    if (*line != '"')
+                        break;
+                    append_text(&new_line, "{\\fs%d}", tag->size);
+                    tag->has_size = true;
+                    has_valid_attr = true;
+                } else if (strncmp(line, "color=\"", 7) == 0) {
+                    line += 7;
+                    if (*line == '#') {
+                        // #RRGGBB format
+                        line++;
+                        tag->color = strtol(line, &line, 16) & 0x00ffffff;
+                        if (*line != '"')
+                            break;
+                        tag->color = ((tag->color & 0xff) << 16)
+                            | (tag->color & 0xff00)
+                            | ((tag->color & 0xff0000) >> 16);
+                    } else {
+                        // Standard web colors
+                        int len = indexof(line, '"');
+                        if (len <= 0)
+                            break;
+                        for (int i = 0; i < FF_ARRAY_ELEMS(subrip_web_colors); i++) {
+                            char *color = subrip_web_colors[i].s;
+                            if (strlen(color) == len
+                                && strncasecmp(line, color, len) == 0) {
+                                tag->color = subrip_web_colors[i].v;
+                                goto foundcolor;
+                            }
+                        }
+
+                        /* We didn't find any matching color */
+                        mp_tmsg(MSGT_SUBREADER, MSGL_WARN,
+                                "SubRip: unknown font color in subtitle: %s\n", orig);
+                        append_text(&new_line, "{\\c}");
+                        line += len + 1;
+                        continue;
+
+                    foundcolor:
+                        line += len;
+                    }
+                    append_text(&new_line, "{\\c&H%06X&}", tag->color);
+                    tag->has_color = true;
+                    has_valid_attr = true;
+                } else if (strncmp(line, "face=\"", 6) == 0) {
+                    /* Font face attribute */
+                    line += 6;
+                    int len = indexof(line, '"');
+                    if (len <= 0)
+                        break;
+                    tag->face.start = line;
+                    tag->face.len = len;
+                    line += len;
+                    append_text(&new_line, "{\\fn%.*s}", BSTR_P(tag->face));
+                    tag->has_face = true;
+                    has_valid_attr = true;
+                }
+                line++;
+            }
+
+            if (!has_valid_attr || *line != '>') { /* Not valid font tag */
+                line = potential_font_tag_start;
+                new_line.len = len_backup;
+            } else {
+                sp++;
+                line++;
+            }
+        }
+
+        /* Tag conversion code didn't match */
+        if (line == orig_line)
+            new_line.buf[new_line.len++] = *line++;
+    }
+    new_line.buf[new_line.len] = 0;
+}
+
+
+/*
+ *      MicroDVD
+ *
+ *      Based on the specifications found here:
+ *      https://trac.videolan.org/vlc/ticket/1825#comment:6
+ */
+
+struct microdvd_tag {
+    char key;
+    int persistent;
+    uint32_t data1;
+    uint32_t data2;
+    struct bstr data_string;
+};
+
+#define MICRODVD_PERSISTENT_OFF     0
+#define MICRODVD_PERSISTENT_ON      1
+#define MICRODVD_PERSISTENT_OPENED  2
+
+// Color, Font, Size, cHarset, stYle, Position, cOordinate
+#define MICRODVD_TAGS               "cfshyYpo"
+
+static void microdvd_set_tag(struct microdvd_tag *tags, struct microdvd_tag tag)
+{
+    int tag_index = indexof(MICRODVD_TAGS, tag.key);
+
+    if (tag_index < 0)
+        return;
+    memcpy(&tags[tag_index], &tag, sizeof(tag));
+}
+
+// italic, bold, underline, strike-through
+#define MICRODVD_STYLES             "ibus"
+
+static char *microdvd_load_tags(struct microdvd_tag *tags, char *s)
+{
+    while (*s == '{') {
+        char *start = s;
+        char tag_char = *(s + 1);
+        struct microdvd_tag tag = {0};
+
+        if (!tag_char || *(s + 2) != ':')
+            break;
+        s += 3;
+
+        switch (tag_char) {
+
+        /* Style */
+        case 'Y':
+            tag.persistent = MICRODVD_PERSISTENT_ON;
+        case 'y':
+            while (*s && *s != '}') {
+                int style_index = indexof(MICRODVD_STYLES, *s);
+
+                if (style_index >= 0)
+                    tag.data1 |= (1 << style_index);
+                s++;
+            }
+            if (*s != '}')
+                break;
+            /* We must distinguish persistent and non-persistent styles
+             * to handle this kind of style tags: {y:ib}{Y:us} */
+            tag.key = tag_char;
+            break;
+
+        /* Color */
+        case 'C':
+            tag.persistent = MICRODVD_PERSISTENT_ON;
+        case 'c':
+            tag.data1 = strtol(s, &s, 16) & 0x00ffffff;
+            if (*s != '}')
+                break;
+            tag.key = 'c';
+            break;
+
+        /* Font name */
+        case 'F':
+            tag.persistent = MICRODVD_PERSISTENT_ON;
+        case 'f':
+        {
+            int len = indexof(s, '}');
+            if (len < 0)
+                break;
+            tag.data_string.start = s;
+            tag.data_string.len = len;
+            s += len;
+            tag.key = 'f';
+            break;
+        }
+
+        /* Font size */
+        case 'S':
+            tag.persistent = MICRODVD_PERSISTENT_ON;
+        case 's':
+            tag.data1 = strtol(s, &s, 10);
+            if (*s != '}')
+                break;
+            tag.key = 's';
+            break;
+
+        /* Charset */
+        case 'H':
+        {
+            //TODO: not yet handled, just parsed.
+            int len = indexof(s, '}');
+            if (len < 0)
+                break;
+            tag.data_string.start = s;
+            tag.data_string.len = len;
+            s += len;
+            tag.key = 'h';
+            break;
+        }
+
+        /* Position */
+        case 'P':
+            tag.persistent = MICRODVD_PERSISTENT_ON;
+            tag.data1 = (*s++ == '1');
+            if (*s != '}')
+                break;
+            tag.key = 'p';
+            break;
+
+        /* Coordinates */
+        case 'o':
+            tag.persistent = MICRODVD_PERSISTENT_ON;
+            tag.data1 = strtol(s, &s, 10);
+            if (*s != ',')
+                break;
+            s++;
+            tag.data2 = strtol(s, &s, 10);
+            if (*s != '}')
+                break;
+            tag.key = 'o';
+            break;
+
+        default:    /* Unknown tag, we consider it to be text */
+            break;
+        }
+
+        if (tag.key == 0)
+            return start;
+
+        microdvd_set_tag(tags, tag);
+        s++;
+    }
+    return s;
+}
+
+static void microdvd_open_tags(struct line *new_line, struct microdvd_tag *tags)
+{
+    for (int i = 0; i < sizeof(MICRODVD_TAGS) - 1; i++) {
+        if (tags[i].persistent == MICRODVD_PERSISTENT_OPENED)
+            continue;
+        switch (tags[i].key) {
+        case 'Y':
+        case 'y':
+            for (int sidx = 0; sidx < sizeof(MICRODVD_STYLES) - 1; sidx++)
+                if (tags[i].data1 & (1 << sidx))
+                    append_text(new_line, "{\\%c1}", MICRODVD_STYLES[sidx]);
+            break;
+
+        case 'c':
+            append_text(new_line, "{\\c&H%06X&}", tags[i].data1);
+            break;
+
+        case 'f':
+            append_text(new_line, "{\\fn%.*s}", BSTR_P(tags[i].data_string));
+            break;
+
+        case 's':
+            append_text(new_line, "{\\fs%d}", tags[i].data1);
+            break;
+
+        case 'p':
+            if (tags[i].data1 == 0)
+                append_text(new_line, "{\\an8}");
+            break;
+
+        case 'o':
+            append_text(new_line, "{\\pos(%d,%d)}",
+                        tags[i].data1, tags[i].data2);
+            break;
+        }
+        if (tags[i].persistent == MICRODVD_PERSISTENT_ON)
+            tags[i].persistent = MICRODVD_PERSISTENT_OPENED;
+    }
+}
+
+static void microdvd_close_no_persistent_tags(struct line *new_line,
+                                              struct microdvd_tag *tags)
+{
+    int i;
+
+    for (i = sizeof(MICRODVD_TAGS) - 2; i; i--) {
+        if (tags[i].persistent != MICRODVD_PERSISTENT_OFF)
+            continue;
+        switch (tags[i].key) {
+
+        case 'y':
+            for (int sidx = sizeof(MICRODVD_STYLES) - 2; sidx >= 0; sidx--)
+                if (tags[i].data1 & (1 << sidx))
+                    append_text(new_line, "{\\%c0}", MICRODVD_STYLES[sidx]);
+            break;
+
+        case 'c':
+            append_text(new_line, "{\\c}");
+            break;
+
+        case 'f':
+            append_text(new_line, "{\\fn}");
+            break;
+
+        case 's':
+            append_text(new_line, "{\\fs}");
+            break;
+        }
+        tags[i].key = 0;
+    }
+}
+
+void subassconvert_microdvd(const char *orig, char *dest, int dest_buffer_size)
+{
+    /* line is not const to avoid warnings with strtol, etc.
+     * orig content won't be changed */
+    char *line = (char *)orig;
+    struct line new_line = {
+        .buf = dest,
+        .bufsize = dest_buffer_size,
+    };
+    struct microdvd_tag tags[sizeof(MICRODVD_TAGS) - 1] = {{0}};
+
+    while (*line) {
+        line = microdvd_load_tags(tags, line);
+        microdvd_open_tags(&new_line, tags);
+
+        while (*line && *line != '|')
+            new_line.buf[new_line.len++] = *line++;
+
+        if (*line == '|') {
+            microdvd_close_no_persistent_tags(&new_line, tags);
+            append_text(&new_line, "\\N");
+            line++;
+        }
+    }
+    new_line.buf[new_line.len] = 0;
+}
diff --git a/sub/subassconvert.h b/sub/subassconvert.h
new file mode 100644
index 0000000000..e6a4425198
--- /dev/null
+++ b/sub/subassconvert.h
@@ -0,0 +1,27 @@
+/*
+ * Header for subtitles converter to SSA/ASS
+ *
+ * This file is part of MPlayer.
+ *
+ * MPlayer 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.
+ *
+ * MPlayer 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 MPlayer; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPLAYER_SUBASSCONVERT_H
+#define MPLAYER_SUBASSCONVERT_H
+
+void subassconvert_subrip(const char *orig, char *dest, int dest_buffer_size);
+void subassconvert_microdvd(const char *orig, char *dest, int dest_buffer_size);
+
+#endif