avfilter/vf_subtitles: Respect YCbCr Matrix header

As specified in libass's ass_types.h, the colors or ASS_Images
should be converted to YCbCr using the matrix/range specified in
the track's YCbCrMatrix field (unless that field is set to YCBCR_NONE,
and defaulting to TV.601 if the header is missing).

This does not affect any subtitles generated or transcoded by ffmpeg,
since these contain a 'YCbCrMatrix: None' header.

Signed-off-by: arch1t3cht <arch1t3cht@gmail.com>
Signed-off-by: rcombs <rcombs@rcombs.me>

libavfilter/vf_subtitles.c

@@ -88,6 +88,40 @@ static const int ass_libavfilter_log_level_map[] = {
     [7] = AV_LOG_DEBUG,     /* MSGL_DBG2 */
 };
 
+static enum AVColorSpace ass_get_color_space(ASS_YCbCrMatrix ass_matrix, enum AVColorSpace inlink_space) {
+    switch (ass_matrix) {
+    case YCBCR_NONE:            return inlink_space;
+    case YCBCR_SMPTE240M_TV:
+    case YCBCR_SMPTE240M_PC:    return AVCOL_SPC_SMPTE240M;
+    case YCBCR_FCC_TV:
+    case YCBCR_FCC_PC:          return AVCOL_SPC_FCC;
+    case YCBCR_BT709_TV:
+    case YCBCR_BT709_PC:        return AVCOL_SPC_BT709;
+    case YCBCR_BT601_TV:
+    case YCBCR_BT601_PC:
+    case YCBCR_DEFAULT:
+    case YCBCR_UNKNOWN:
+    default:                    return AVCOL_SPC_SMPTE170M;
+    }
+}
+
+static enum AVColorRange ass_get_color_range(ASS_YCbCrMatrix ass_matrix, enum AVColorRange inlink_range) {
+    switch (ass_matrix) {
+    case YCBCR_NONE:            return inlink_range;
+    case YCBCR_SMPTE240M_PC:
+    case YCBCR_FCC_PC:
+    case YCBCR_BT709_PC:
+    case YCBCR_BT601_PC:        return AVCOL_RANGE_JPEG;
+    case YCBCR_SMPTE240M_TV:
+    case YCBCR_FCC_TV:
+    case YCBCR_BT709_TV:
+    case YCBCR_BT601_TV:
+    case YCBCR_DEFAULT:
+    case YCBCR_UNKNOWN:
+    default:                    return AVCOL_RANGE_MPEG;
+    }
+}
+
 static void ass_log(int ass_level, const char *fmt, va_list args, void *ctx)
 {
     const int ass_level_clip = av_clip(ass_level, 0,
@@ -150,7 +184,9 @@ static int config_input(AVFilterLink *inlink)
 {
     AssContext *ass = inlink->dst->priv;
 
-    ff_draw_init2(&ass->draw, inlink->format, inlink->colorspace, inlink->color_range,
+    ff_draw_init2(&ass->draw, inlink->format,
+                  ass_get_color_space(ass->track->YCbCrMatrix, inlink->colorspace),
+                  ass_get_color_range(ass->track->YCbCrMatrix, inlink->color_range),
                   ass->alpha ? FF_DRAW_PROCESS_ALPHA : 0);
 
     ass_set_frame_size  (ass->renderer, inlink->w, inlink->h);