sub: make filter_sdh a "proper" filter, allow runtime changes

Until now, filter_sdh was simply a function that was called by sd_ass
directly (if enabled).

I want to add another filter, so it's time to turn this into a somewhat
more general subtitle filtering infrastructure.

I pondered whether to reuse the audio/video filtering stuff - but better
not. Also, since subtitles are horrible and tend to refuse proper
abstraction, it's still messed into sd_ass, instead of working on the
dec_sub.c level. Actually mpv used to have subtitle "filters" and even
made subtitle converters part of it, but it was fairly horrible, so
don't do that again.

In addition, make runtime changes possible. Since this was supposed to
be a quick hack, I just decided to put all subtitle filter options into
a separate option group (=> simpler change notification), to manually
push the change through the playloop (like it was sort of before for OSD
options), and to recreate the sub filter chain completely in every
change. Should be good enough.

One strangeness is that due to prefetching and such, most subtitle
packets (or those some time ahead) are actually done filtering when we
change, so the user still needs to manually seek to actually refresh
everything. And since subtitle data is usually cached in ASS_Track (for
other terrible but user-friendly reasons), we also must clear the
subtitle data, but of course only on seek, since otherwise all subtitles
would just disappear. What a fucking mess, but such is life. We could
trigger a "refresh seek" to make this more automatic, but I don't feel
like it currently.

This is slightly inefficient (lots of allocations and copying), but I
decided that it doesn't matter. Could matter slightly for crazy ASS
subtitles that render with thousands of events.

Not very well tested. Still seems to work, but I didn't have many test
cases.

1 files changed, 52 insertions, 9 deletions

diff --git a/sub/filter_sdh.c b/sub/filter_sdh.c
index 72744ec20e..2b544ea222 100644
--- a/sub/filter_sdh.c
+++ b/sub/filter_sdh.c
@@ -15,9 +15,11 @@
  * License along with mpv.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#include <stdlib.h>
 #include <assert.h>
+#include <stdlib.h>
 #include <string.h>
+#include <limits.h>
+
 #include "misc/ctype.h"
 #include "common/common.h"
 #include "common/msg.h"
@@ -43,7 +45,7 @@ static void init_buf(struct buffer *buf, int length)
     buf->length = length;
 }
 
-static inline int append(struct sd *sd, struct buffer *buf, char c)
+static inline int append(struct sd_filter *sd, struct buffer *buf, char c)
 {
     if (buf->pos >= 0 && buf->pos < buf->length) {
         buf->string[buf->pos++] = c;
@@ -66,7 +68,7 @@ static inline int append(struct sd *sd, struct buffer *buf, char c)
 //
 // on return the read pointer is updated to the position after
 // the tags.
-static void copy_ass(struct sd *sd, char **rpp, struct buffer *buf)
+static void copy_ass(struct sd_filter *sd, char **rpp, struct buffer *buf)
 {
     char *rp = *rpp;
 
@@ -83,7 +85,7 @@ static void copy_ass(struct sd *sd, char **rpp, struct buffer *buf)
     return;
 }
 
-static bool skip_bracketed(struct sd *sd, char **rpp, struct buffer *buf);
+static bool skip_bracketed(struct sd_filter *sd, char **rpp, struct buffer *buf);
 
 // check for speaker label, like MAN:
 // normal subtitles may include mixed case text with : after so
@@ -101,7 +103,7 @@ static bool skip_bracketed(struct sd *sd, char **rpp, struct buffer *buf);
 // if no label was found read pointer and write position in buffer
 // will be unchanged
 // otherwise they point to next position after label and next write position
-static void skip_speaker_label(struct sd *sd, char **rpp, struct buffer *buf)
+static void skip_speaker_label(struct sd_filter *sd, char **rpp, struct buffer *buf)
 {
     int filter_harder = sd->opts->sub_filter_SDH_harder;
     char *rp = *rpp;
@@ -187,7 +189,7 @@ static void skip_speaker_label(struct sd *sd, char **rpp, struct buffer *buf)
 // return true if bracketed text was removed.
 // if not valid SDH read pointer and write buffer position will be unchanged
 // otherwise they point to next position after text and next write position
-static bool skip_bracketed(struct sd *sd, char **rpp, struct buffer *buf)
+static bool skip_bracketed(struct sd_filter *sd, char **rpp, struct buffer *buf)
 {
     char *rp = *rpp;
     int old_pos = buf->pos;
@@ -235,7 +237,7 @@ static bool skip_bracketed(struct sd *sd, char **rpp, struct buffer *buf)
 // return true if paranthesed text was removed.
 // if not valid SDH read pointer and write buffer position will be unchanged
 // otherwise they point to next position after text and next write position
-static bool skip_parenthesed(struct sd *sd, char **rpp, struct buffer *buf)
+static bool skip_parenthesed(struct sd_filter *sd, char **rpp, struct buffer *buf)
 {
     int filter_harder = sd->opts->sub_filter_SDH_harder;
     char *rp = *rpp;
@@ -289,7 +291,8 @@ static bool skip_parenthesed(struct sd *sd, char **rpp, struct buffer *buf)
 //
 // when removing characters the following are moved back
 //
-static void remove_leading_hyphen_space(struct sd *sd, int start_pos, struct buffer *buf)
+static void remove_leading_hyphen_space(struct sd_filter *sd, int start_pos,
+                                        struct buffer *buf)
 {
     int old_pos = buf->pos;
     if (start_pos < 0 || start_pos >= old_pos)
@@ -340,7 +343,8 @@ static void remove_leading_hyphen_space(struct sd *sd, int start_pos, struct buf
 //
 // Returns NULL if filtering resulted in all of ASS data being removed so no
 // subtitle should be output
-char *filter_SDH(struct sd *sd, char *format, int n_ignored, char *data, int length)
+static char *filter_SDH(struct sd_filter *sd, char *format, int n_ignored,
+                        char *data, int length)
 {
     if (!format) {
         MP_VERBOSE(sd, "SDH filtering not possible - format missing\n");
@@ -462,3 +466,42 @@ char *filter_SDH(struct sd *sd, char *format, int n_ignored, char *data, int len
         return NULL;
     }
 }
+
+static bool sdh_init(struct sd_filter *ft)
+{
+    if (strcmp(ft->codec, "ass") != 0)
+        return false;
+
+    if (!ft->opts->sub_filter_SDH)
+        return false;
+
+    return true;
+}
+
+static struct demux_packet *sdh_filter(struct sd_filter *ft,
+                                       struct demux_packet *pkt)
+{
+    char *line = (char *)pkt->buffer;
+    size_t len = pkt->len;
+    if (len >= INT_MAX)
+        return NULL;
+
+    line = filter_SDH(ft, ft->event_format, 1, line, len);
+    if (!line)
+        return NULL;
+
+    // Stupidly, this copies it again. One could possibly allocate the packet
+    // for writing in the first place (new_demux_packet()) and use
+    // demux_packet_shorten(). Or not allocate anything on no change.
+    struct demux_packet *npkt = new_demux_packet_from(line, strlen(line));
+    if (npkt)
+        demux_packet_copy_attribs(npkt, pkt);
+
+    talloc_free(line);
+    return npkt;
+}
+
+const struct sd_filter_functions sd_filter_sdh = {
+    .init   = sdh_init,
+    .filter = sdh_filter,
+};