sd_lavc: enable teletext

Whitelisting supported codecs is (probably) still better than just
allowing everything, given the weird FFmpeg API. I'm also assuming
Libav doesn't even have the codec ID, but I didn't check.

Also add a --teletext-page option, since otherwise it decodes every
teletext page and shows them in succession.

And yes, we can't use av_opt_set_int() - instead we have to set it as
string. Because FFmpeg's option system is terrible.

DOCS/man/options.rst

@@ -1795,6 +1795,10 @@ Subtitles
     of subtitles across seeks, so after a seek libass can't eliminate subtitle
     packets with the same ReadOrder as earlier packets.
 
+``--teletext-page=<1-999>``
+    This works for ``dvb_teletext`` subtitle streams, and if FFmpeg has been
+    compiled with support for it.
+
 Window
 ------
 

options/options.c

@@ -469,6 +469,7 @@ const m_option_t mp_opts[] = {
     OPT_SUBSTRUCT("osd", osd_style, osd_style_conf, 0),
     OPT_SUBSTRUCT("sub-text", sub_text_style, sub_style_conf, 0),
     OPT_FLAG("sub-clear-on-seek", sub_clear_on_seek, 0),
+    OPT_INTRANGE("teletext-page", teletext_page, 0, 1, 999),
 
 //---------------------- libao/libvo options ------------------------
     OPT_SETTINGSLIST("ao", audio_driver_list, 0, &ao_obj_list, ),
@@ -776,6 +777,7 @@ const struct MPOpts mp_default_opts = {
     .sub_use_margins = 1,
     .ass_scale_with_window = 0,
     .sub_scale_with_window = 1,
+    .teletext_page = 100,
 #if HAVE_LUA
     .lua_load_osc = 1,
     .lua_load_ytdl = 1,

options/options.h

@@ -281,6 +281,7 @@ typedef struct MPOpts {
     int ass_hinting;
     int ass_shaper;
     int sub_clear_on_seek;
+    int teletext_page;
 
     int hwdec_api;
     char *hwdec_codecs;

sub/sd_lavc.c

@@ -22,6 +22,7 @@
 #include <libavcodec/avcodec.h>
 #include <libavutil/common.h>
 #include <libavutil/intreadwrite.h>
+#include <libavutil/opt.h>
 
 #include "config.h"
 
@@ -106,6 +107,9 @@ static int init(struct sd *sd)
     // Supported codecs must be known to decode to paletted bitmaps
     switch (cid) {
     case AV_CODEC_ID_DVB_SUBTITLE:
+#if LIBAVCODEC_VERSION_MICRO >= 100
+    case AV_CODEC_ID_DVB_TELETEXT:
+#endif
     case AV_CODEC_ID_HDMV_PGS_SUBTITLE:
     case AV_CODEC_ID_XSUB:
     case AV_CODEC_ID_DVD_SUBTITLE:
@@ -339,6 +343,13 @@ static void decode(struct sd *sd, struct demux_packet *packet)
         MP_WARN(sd, "Subtitle with unknown start time.\n");
 
     mp_set_av_packet(&pkt, packet, &priv->pkt_timebase);
+
+    if (ctx->codec_id == AV_CODEC_ID_DVB_TELETEXT) {
+        char page[4];
+        snprintf(page, sizeof(page), "%d", opts->teletext_page);
+        av_opt_set(ctx, "txt_page", page, AV_OPT_SEARCH_CHILDREN);
+    }
+
     int got_sub;
     int res = avcodec_decode_subtitle2(ctx, &sub, &got_sub, &pkt);
     if (res < 0 || !got_sub)