Fix font loading when attachments precede tracks in MKV

lib_ass_media/src/main/java/io/github/peerless2012/ass/media/AssHandler.kt

@@ -53,6 +53,9 @@ class AssHandler(
     /** The available ASS tracks in the current media. */
     private val availableTracks = mutableMapOf<String, AssTrack>()
 
+    /** Fonts encountered before any ASS track was created. Flushed in [createTrack]. */
+    private val pendingFonts = mutableListOf<Pair<String, ByteArray>>()
+
     /** The size of the video track. */
     var videoSize = Size.ZERO
         private set
@@ -114,6 +117,7 @@ class AssHandler(
         render = null
         track = null
         availableTracks.clear()
+        pendingFonts.clear()
         videoSize = Size.ZERO
         videoTime = -1
         videoFrameIndex = 0
@@ -216,6 +220,19 @@ class AssHandler(
         return availableTracks.isNotEmpty()
     }
 
+    /**
+     * Adds a font to the ASS library. If no tracks have been created yet, the font is buffered
+     * and will be added when the first track is created via [createTrack].
+     */
+    @Synchronized
+    fun addFont(name: String, data: ByteArray) {
+        if (hasTracks()) {
+            ass.addFont(name, data)
+        } else {
+            pendingFonts.add(name to data)
+        }
+    }
+
     /**
      * Creates a new ASS track from the given format and saves it in the [availableTracks].
      * The renderer and libass are also created if needed.
@@ -228,6 +245,14 @@ class AssHandler(
         // Ensure the renderer is created before creating tracks.
         createRenderIfNeeded()
 
+        // Flush any fonts that were buffered before the first track was created.
+        if (pendingFonts.isNotEmpty()) {
+            for ((name, data) in pendingFonts) {
+                ass.addFont(name, data)
+            }
+            pendingFonts.clear()
+        }
+
         val track = ass.createTrack()
         if (format.initializationData.size > 0) {
             val header = AssHeaderParser.parse(format, renderType != AssRenderType.CUES)

lib_ass_media/src/main/java/io/github/peerless2012/ass/media/extractor/AssMatroskaExtractor.kt

@@ -84,11 +84,10 @@ class AssMatroskaExtractor(
                 val attachmentName = requireNotNull(currentAttachmentName)
                 val attachmentMime = requireNotNull(currentAttachmentMime)
 
-                // Only add fonts if an ASS track was detected to support lazy initialization
-                if (assHandler.hasTracks() && attachmentMime in fontMimeTypes) {
+                if (attachmentMime in fontMimeTypes) {
                     val data = ByteArray(contentSize)
                     input.readFully(data, 0, contentSize)
-                    assHandler.ass.addFont(attachmentName, data)
+                    assHandler.addFont(attachmentName, data)
                 } else {
                     input.skipFully(contentSize)
                 }