demux_mkv: check if the video codec is an image

Add a simple helper to codec_tags to check if the codec name matches one
of the images. If so, then we set still_image and image in the stream as
true (slightly different semanatics).

demux/codec_tags.c

@@ -233,6 +233,17 @@ static const char *const type_to_codec[][2] = {
     {0}
 };
 
+bool mp_codec_is_image(const char *codec)
+{
+    if (codec) {
+        for (int n = 0; type_to_codec[n][0]; n++) {
+            if (strcasecmp(type_to_codec[n][1], codec) == 0)
+                return true;
+        }
+    }
+    return false;
+}
+
 const char *mp_map_type_to_image_codec(const char *type)
 {
     if (type) {

demux/codec_tags.h

@@ -28,6 +28,7 @@ void mp_set_codec_from_tag(struct mp_codec_params *c);
 void mp_set_pcm_codec(struct mp_codec_params *c, bool sign, bool is_float,
                       int bits, bool is_be);
 
+bool mp_codec_is_image(const char *codec);
 const char *mp_map_type_to_image_codec(const char *type);
 const char *mp_map_mimetype_to_video_codec(const char *mimetype);
 

demux/demux_mkv.c

@@ -1484,6 +1484,10 @@ static int demux_mkv_open_video(demuxer_t *demuxer, mkv_track_t *track)
     }
 
     const char *codec = sh_v->codec ? sh_v->codec : "";
+    if (mp_codec_is_image(codec)) {
+        sh->still_image = true;
+        sh->image = true;
+    }
     if (!strcmp(codec, "mjpeg")) {
         sh_v->codec_tag = MKTAG('m', 'j', 'p', 'g');
         track->require_keyframes = true;