sub: add closest subtitle option using Levenshtein distance

DOCS/man/options.rst

@@ -2826,16 +2826,19 @@ Subtitles
         rendering of ASS/SSA subtitles. It can sometimes be useful to forcibly
         override the styling of ASS subtitles, but should be avoided in general.
 
-``--sub-auto=<no|exact|fuzzy|all>``
+``--sub-auto=<no|exact|fuzzy|all|closest>``
     Load additional subtitle files matching the video filename. The parameter
     specifies how external subtitle files are matched. ``exact`` is enabled by
     default.
 
     :no:    Don't automatically load external subtitle files.
     :exact: Load the media filename with subtitle file extension and possibly
             language suffixes (default).
-    :fuzzy: Load all subs containing the media filename.
-    :all:   Load all subs in the current and ``--sub-file-paths`` directories.
+    :fuzzy:   Load all subs containing the media filename.
+    :all:     Load all subs in the current and ``--sub-file-paths`` directories.
+    :closest: Load exactly one external subtitle: the single file whose filename
+              is most similar to the media's base name. Language/flag suffixes
+              like ``.en``, ``.eng``, ``.forced`` are ignored for similarity.
 
 ``--sub-auto-exts=ext1,ext2,...``
     Subtitle extensions to try and match when using ``--sub-auto``. Note that

demux/demux_mf.c

@@ -100,7 +100,7 @@ static mf_t *open_mf_pattern(void *talloc_ctx, struct demuxer *d, char *filename
     }
 
     if (strchr(filename, ',')) {
-        mp_info(log, "filelist: %s\n", filename);
+        mp_info(log, "filelist: %s\n", filename ? filename : "(null)");
         bstr bfilename = bstr0(filename);
 
         while (bfilename.len) {
@@ -191,15 +191,15 @@ static mf_t *open_mf_pattern(void *talloc_ctx, struct demuxer *d, char *filename
     if (bad_spec || nspec != 1) {
         mp_err(log,
                "unsupported expr format: '%s' - exactly one format specifier of the form %%[.][NUM]d is expected\n",
-               filename);
+               filename ? filename : "(null)");
         goto exit_mf;
     }
 
-    mp_info(log, "search expr: %s\n", filename);
+    mp_info(log, "search expr: %s\n", filename ? filename : "(null)");
 
     while (error_count < 5) {
         if (snprintf(fname, fname_avail, filename, count++) >= fname_avail) {
-            mp_err(log, "format result too long: '%s'\n", filename);
+            mp_err(log, "format result too long: '%s'\n", filename ? filename : "(null)");
             goto exit_mf;
         }
         if (!mp_path_exists(fname)) {

meson.build

@@ -142,6 +142,7 @@ sources = files(
     'misc/json.c',
     'misc/language.c',
     'misc/natural_sort.c',
+    'misc/string_similarity.c',
     'misc/node.c',
     'misc/path_utils.c',
     'misc/random.c',

misc/language.c

@@ -22,6 +22,7 @@
 
 #include "common/common.h"
 #include "misc/ctype.h"
+#include <string.h>
 
 #define L(s) { #s, sizeof(#s) - 1 }
 
@@ -297,6 +298,27 @@ int mp_match_lang(char **langs, const char *lang)
     return best_score;
 }
 
+bool mp_language_is_suffix_token(const char *token)
+{
+    if (!token || !token[0])
+        return false;
+
+    char *lang_list[] = {(char *)token, NULL};
+    if (mp_match_lang(lang_list, token) > 0)
+        return true;
+
+    static const char *const special[] = {
+        "jp", "chs", "cht", "sub", "subs", "sdh", "forced", "cc", NULL,
+    };
+
+    for (int i = 0; special[i]; i++) {
+        if (strcmp(token, special[i]) == 0)
+            return true;
+    }
+
+    return false;
+}
+
 bstr mp_guess_lang_from_filename(bstr name, int *lang_start, enum track_flags *flags)
 {
     name = bstr_strip(bstr_strip_ext(name));

misc/language.h

@@ -20,12 +20,15 @@
 #ifndef MP_LANGUAGE_H
 #define MP_LANGUAGE_H
 
+#include <stdbool.h>
+
 #include "misc/bstr.h"
 #include "common/common.h"
 
 // Result numerically higher => better match. 0 == no match.
 int mp_match_lang(char **langs, const char *lang);
 char **mp_get_user_langs(void);
 bstr mp_guess_lang_from_filename(bstr name, int *lang_start, enum track_flags *flags);
+bool mp_language_is_suffix_token(const char *token);
 
 #endif /* MP_LANGUAGE_H */

misc/string_similarity.c

@@ -0,0 +1,96 @@
+/*
+ * This file is part of mpv.
+ *
+ * mpv is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * mpv 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with mpv.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <ctype.h>
+#include <string.h>
+
+#include "mpv_talloc.h"
+
+#include "common/common.h"
+#include "misc/bstr.h"
+#include "misc/language.h"
+#include "misc/path_utils.h"
+#include "misc/string_similarity.h"
+
+static bool is_suffix_token(const char *tkn)
+{
+    return mp_language_is_suffix_token(tkn);
+}
+
+char *mp_normalize_base_name(void *ta_ctx, const char *path)
+{
+    struct bstr base = bstr0(mp_basename(path));
+    base = bstr_strip_ext(base);
+    char *tmpbuf = talloc_strndup(ta_ctx, base.start, base.len);
+    for (int i = 0; tmpbuf[i]; i++)
+        tmpbuf[i] = tolower((unsigned char)tmpbuf[i]);
+    char **tokens = NULL;
+    int ntok = 0;
+    char *p = tmpbuf;
+    while (*p) {
+        while (*p && !isalnum((unsigned char)*p)) p++;
+        if (!*p) break;
+        char *start = p;
+        while (*p && isalnum((unsigned char)*p)) p++;
+        char save = *p; *p = '\0';
+        MP_TARRAY_APPEND(ta_ctx, tokens, ntok, talloc_strdup(ta_ctx, start));
+        *p = save;
+    }
+    while (ntok > 0 && is_suffix_token(tokens[ntok - 1]))
+        ntok--;
+    char *out = talloc_strdup(ta_ctx, "");
+    for (int i = 0; i < ntok; i++)
+        out = talloc_asprintf_append_buffer(out, "%s", tokens[i]);
+    if (!out[0])
+        out = talloc_strdup(ta_ctx, tmpbuf);
+    return out;
+}
+
+int mp_levenshtein_dist(const char *a, const char *b)
+{
+    int la = (int)strlen(a), lb = (int)strlen(b);
+    if (la == 0) return lb;
+    if (lb == 0) return la;
+    int *prev = talloc_array(NULL, int, lb + 1);
+    int *curr = talloc_array(NULL, int, lb + 1);
+    for (int j = 0; j <= lb; j++) prev[j] = j;
+    for (int i = 1; i <= la; i++) {
+        curr[0] = i;
+        for (int j = 1; j <= lb; j++) {
+            int cost = a[i - 1] == b[j - 1] ? 0 : 1;
+            int del = prev[j] + 1;
+            int ins = curr[j - 1] + 1;
+            int sub = prev[j - 1] + cost;
+            int m = del < ins ? del : ins;
+            curr[j] = m < sub ? m : sub;
+        }
+        int *tmpv = prev; prev = curr; curr = tmpv;
+    }
+    int d = prev[lb];
+    talloc_free(prev);
+    talloc_free(curr);
+    return d;
+}
+
+double mp_similarity_ratio(const char *a, const char *b)
+{
+    int la = (int)strlen(a), lb = (int)strlen(b);
+    int m = la > lb ? la : lb;
+    if (m == 0) return 1.0;
+    int d = mp_levenshtein_dist(a, b);
+    return 1.0 - (double)d / (double)m;
+}

misc/string_similarity.h

@@ -0,0 +1,24 @@
+#pragma once
+
+/*
+ * This file is part of mpv.
+ *
+ * mpv is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * mpv 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with mpv.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stddef.h>
+
+char *mp_normalize_base_name(void *ta_ctx, const char *path);
+double mp_similarity_ratio(const char *a, const char *b);
+int mp_levenshtein_dist(const char *a, const char *b);

options/options.c

@@ -722,7 +722,7 @@ static const m_option_t mp_opts[] = {
     {"autoload-files", OPT_BOOL(autoload_files)},
 
     {"sub-auto", OPT_CHOICE(sub_auto,
-        {"no", -1}, {"exact", 0}, {"fuzzy", 1}, {"all", 2})},
+        {"no", -1}, {"exact", 0}, {"fuzzy", 1}, {"all", 2}, {"closest", 3})},
     {"sub-auto-exts", OPT_STRINGLIST(sub_auto_exts), .flags = UPDATE_SUB_EXTS},
     {"audio-file-auto", OPT_CHOICE(audiofile_auto,
         {"no", -1}, {"exact", 0}, {"fuzzy", 1}, {"all", 2})},