movies: allow seeking compressed Ogg Vorbis file to beginning

panda/src/movies/vorbisAudioCursor.cxx

@@ -91,19 +91,46 @@ seek(double t) {
   t = std::max(t, 0.0);
 
   // Use ov_time_seek_lap if cross-lapping is enabled.
+  int result;
   if (vorbis_seek_lap) {
-    if (ov_time_seek_lap(&_ov, t) != 0) {
-      movies_cat.error()
-        << "Seek failed.  Ogg Vorbis stream may not be seekable.\n";
-      return;
-    }
+    result = ov_time_seek_lap(&_ov, t);
   } else {
-    if (ov_time_seek(&_ov, t) != 0) {
-      movies_cat.error()
-        << "Seek failed.  Ogg Vorbis stream may not be seekable.\n";
+    result = ov_time_seek(&_ov, t);
+  }
+
+  // Special case for seeking to the beginning; if normal seek fails, we may
+  // be able to explicitly seek to the beginning of the file and call ov_open
+  // again.  This allows looping compressed .ogg files.
+  if (result == OV_ENOSEEK && t == 0.0) {
+    std::istream *stream = (std::istream *)_ov.datasource;
+
+    if (stream->rdbuf()->pubseekpos(0, std::ios::in) == 0) {
+      // Back up the callbacks, then destroy the stream, making sure to first
+      // unset the datasource so that it won't close the file.
+      ov_callbacks callbacks = _ov.callbacks;
+      _ov.datasource = nullptr;
+      ov_clear(&_ov);
+
+      if (ov_open_callbacks((void *)stream, &_ov, nullptr, 0, callbacks) != 0) {
+        movies_cat.error()
+          << "Failed to reopen Ogg Vorbis file to seek to beginning.\n";
+        return;
+      }
+
+      // Reset these fields for good measure, just in case the file changed.
+      vorbis_info *vi = ov_info(&_ov, -1);
+      _audio_channels = vi->channels;
+      _audio_rate = vi->rate;
+
+      _last_seek = 0.0;
+      _samples_read = 0;
       return;
     }
   }
+  if (result != 0) {
+    movies_cat.error()
+      << "Seek failed.  Ogg Vorbis stream may not be seekable.\n";
+  }
 
   _last_seek = ov_time_tell(&_ov);
   _samples_read = 0;