demux_mkv: support embedded coverart

The code could as well be in demux.c, but it's better to avoid
accidental clashes with demux_lavf.c.

FFmpeg provides no way yet to map a mime type to a codec, so do it
manually. (It _can_ map a mime type to an "input format", but not a
codec.)

Fixes #1374.

demux/codec_tags.c

@@ -141,3 +141,20 @@ void mp_set_pcm_codec(struct sh_stream *sh, bool sign, bool is_float, int bits,
         mp_snprintf_cat(codec, sizeof(codec), is_be ? "be" : "le");
     sh->codec = talloc_strdup(sh->audio, codec);
 }
+
+static const char *const mimetype_to_codec[][2] = {
+    {"image/jpeg",      "mjpeg"},
+    {"image/png",       "png"},
+    {0}
+};
+
+const char *mp_map_mimetype_to_video_codec(const char *mimetype)
+{
+    if (mimetype) {
+        for (int n = 0; mimetype_to_codec[n][0]; n++) {
+            if (strcmp(mimetype_to_codec[n][0], mimetype) == 0)
+                return mimetype_to_codec[n][1];
+        }
+    }
+    return NULL;
+}

demux/codec_tags.h

@@ -28,4 +28,6 @@ void mp_set_codec_from_tag(struct sh_stream *sh);
 void mp_set_pcm_codec(struct sh_stream *sh, bool sign, bool is_float, int bits,
                       bool is_be);
 
+const char *mp_map_mimetype_to_video_codec(const char *mimetype);
+
 #endif

demux/demux_mkv.c

@@ -1123,7 +1123,20 @@ skip:
     return 0;
 }
 
-
+static void add_coverart(struct demuxer *demuxer)
+{
+    for (int n = 0; n < demuxer->num_attachments; n++) {
+        struct demux_attachment *att = &demuxer->attachments[n];
+        const char *codec = mp_map_mimetype_to_video_codec(att->type);
+        if (!codec)
+            continue;
+        struct sh_stream *sh = new_sh_stream(demuxer, STREAM_VIDEO);
+        if (!sh)
+            break;
+        sh->codec = codec;
+        sh->attached_picture = new_demux_packet_from(att->data, att->data_size);
+    }
+}
 
 static int demux_mkv_open_video(demuxer_t *demuxer, mkv_track_t *track);
 static int demux_mkv_open_audio(demuxer_t *demuxer, mkv_track_t *track);
@@ -1831,6 +1844,7 @@ static int demux_mkv_open(demuxer_t *demuxer, enum demux_check check)
 
     process_tags(demuxer);
     display_create_tracks(demuxer);
+    add_coverart(demuxer);
 
     if (demuxer->opts->mkv_probe_duration)
         probe_last_timestamp(demuxer);