sd_lavc, sd_spu: make dvdsub stretching conditional on --stretch-dvd-subs.

We found that the stretching - although it usually improves the looks of
the fonts - is incorrect.

On DVD, subtitles can cover the full area of the picture, and they have
the same pixel aspect as the movie itself.

Too bad many commercially released DVDs use bitmap fonts made with the
wrong pixel aspect (i.e. assuming 1:1) - --stretch-dvd-subs will make
these more pretty then.

DOCS/man/en/options.rst

@@ -2088,6 +2088,19 @@ OPTIONS
         ``--start='#2' --end='#4'``
             Plays chapters 2 and 3, and exits.
 
+``--stretch-dvd-subs=<yes|no>``
+    Stretch DVD subtitles when playing anamorphic videos for better looking
+    fonts on badly mastered DVDs. This switch has no effect when the
+    video is stored with square pixels - which for DVD input cannot be the case
+    though.
+
+    Many studios tend to use bitmap fonts designed for square pixels when
+    authoring DVDs, causing the fonts to look stretched on playback on DVD
+    players. This option fixes them, however at the price of possibly
+    misaligning sume subtitles (e.g. sign translations).
+
+    Disabled by default.
+
 ``--ssf=<mode>``
     Specifies software scaler parameters.
 

mpvcore/options.c

@@ -531,6 +531,7 @@ const m_option_t mp_opts[] = {
     OPT_FLAG("autosub", sub_auto, 0),
     OPT_FLAG("sub-visibility", sub_visibility, 0),
     OPT_FLAG("sub-forced-only", forced_subs_only, 0),
+    OPT_FLAG("stretch-dvd-subs", stretch_dvd_subs, 0),
     OPT_FLAG_CONSTANTS("sub-fix-timing", suboverlap_enabled, 0, 1, 0),
     OPT_CHOICE("autosub-match", sub_match_fuzziness, 0,
                ({"exact", 0}, {"fuzzy", 1}, {"all", 2})),

mpvcore/options.h

@@ -148,6 +148,7 @@ typedef struct MPOpts {
     float sub_fps;
     float sub_speed;
     int forced_subs_only;
+    int stretch_dvd_subs;
     char *quvi_format;
 
     // subreader.c

sub/sd_lavc.c

@@ -207,6 +207,7 @@ static void get_bitmaps(struct sd *sd, struct mp_osd_res d, double pts,
                         struct sub_bitmaps *res)
 {
     struct sd_lavc_priv *priv = sd->priv;
+    struct MPOpts *opts = sd->opts;
 
     if (priv->pts != MP_NOPTS_VALUE && pts < priv->pts)
         return;
@@ -223,7 +224,8 @@ static void get_bitmaps(struct sd *sd, struct mp_osd_res d, double pts,
     int vidh = d.h - d.mt - d.mb;
     double xscale = (double)vidw / inw;
     double yscale = (double)vidh / inh;
-    if (priv->avctx->codec_id == AV_CODEC_ID_DVD_SUBTITLE) {
+    if (priv->avctx->codec_id == AV_CODEC_ID_DVD_SUBTITLE &&
+            opts->stretch_dvd_subs) {
         // For DVD subs, try to keep the subtitle PAR at display PAR.
         double video_par =
               (priv->video_params.d_w / (double)priv->video_params.d_h)

sub/sd_spu.c

@@ -21,12 +21,14 @@
 #include "talloc.h"
 #include "mpvcore/options.h"
 #include "demux/stheader.h"
+#include "video/mp_image.h"
 #include "sd.h"
 #include "sub.h"
 #include "spudec.h"
 
 struct sd_spu_priv {
     void *spudec;
+    struct mp_image_params video_params;
 };
 
 static bool is_dvd_sub(const char *t)
@@ -72,8 +74,22 @@ static void get_bitmaps(struct sd *sd, struct mp_osd_res d, double pts,
     spudec_set_forced_subs_only(priv->spudec, opts->forced_subs_only);
     spudec_heartbeat(priv->spudec, pts * 90000);
 
-    if (spudec_visible(priv->spudec))
-        spudec_get_indexed(priv->spudec, &d, res);
+    if (spudec_visible(priv->spudec)) {
+        double xscale = 1;
+        double yscale = 1;
+        if (opts->stretch_dvd_subs) {
+            // For DVD subs, try to keep the subtitle PAR at display PAR.
+            double video_par =
+                  (priv->video_params.d_w / (double)priv->video_params.d_h)
+                / (priv->video_params.w   / (double)priv->video_params.h);
+            if (video_par > 1.0) {
+                xscale /= video_par;
+            } else {
+                yscale *= video_par;
+            }
+        }
+        spudec_get_indexed(priv->spudec, &d, xscale, yscale, res);
+    }
 }
 
 static void reset(struct sd *sd)
@@ -91,12 +107,25 @@ static void uninit(struct sd *sd)
     talloc_free(priv);
 }
 
+static int control(struct sd *sd, enum sd_ctrl cmd, void *arg)
+{
+    struct sd_spu_priv *priv = sd->priv;
+    switch (cmd) {
+    case SD_CTRL_SET_VIDEO_PARAMS:
+        priv->video_params = *(struct mp_image_params *)arg;
+        return CONTROL_OK;
+    default:
+        return CONTROL_UNKNOWN;
+    }
+}
+
 const struct sd_functions sd_spu = {
     .name = "spu",
     .supports_format = supports_format,
     .init = init,
     .decode = decode,
     .get_bitmaps = get_bitmaps,
+    .control = control,
     .reset = reset,
     .uninit = uninit,
 };

sub/spudec.c

@@ -644,6 +644,7 @@ void spudec_set_forced_subs_only(void * const this, const unsigned int flag)
 }
 
 void spudec_get_indexed(void *this, struct mp_osd_res *dim,
+                        double xstretch, double ystretch,
                         struct sub_bitmaps *res)
 {
     spudec_handle_t *spu = this;
@@ -656,10 +657,10 @@ void spudec_get_indexed(void *this, struct mp_osd_res *dim,
     if (spudec_visible(spu) && !empty) {
         double xscale = (double) (dim->w - dim->ml - dim->mr) / spu->orig_frame_width;
         double yscale = (double) (dim->h - dim->mt - dim->mb) / spu->orig_frame_height;
-        part->x = part->x * xscale + dim->ml;
-        part->y = part->y * yscale + dim->mt;
-        part->dw = part->w * xscale;
-        part->dh = part->h * yscale;
+        part->x = part->x * xscale * xstretch + dim->ml + dim->w * (0.5 - 0.5 * xstretch);
+        part->y = part->y * yscale * ystretch + dim->mt + dim->h * (0.5 - 0.5 * ystretch);
+        part->dw = part->w * xscale * xstretch;
+        part->dh = part->h * yscale * ystretch;
         res->num_parts = 1;
         res->scaled = true;
     }

sub/spudec.h

@@ -26,7 +26,7 @@ struct mp_osd_res;
 
 void spudec_heartbeat(void *this, unsigned int pts100);
 void spudec_assemble(void *this, unsigned char *packet, unsigned int len, int pts100);
-void spudec_get_indexed(void *this, struct mp_osd_res *dim, struct sub_bitmaps *res);
+void spudec_get_indexed(void *this, struct mp_osd_res *dim, double xstretch, double ystretch, struct sub_bitmaps *res);
 void *spudec_new_scaled(unsigned int frame_width, unsigned int frame_height, uint8_t *extradata, int extradata_len);
 void spudec_free(void *this);
 void spudec_reset(void *this);	// called after seek