obs-ffmpeg: Pass correct audio codec to muxer subprocess

plugins/obs-ffmpeg/obs-ffmpeg-mux.c

@@ -313,7 +313,9 @@ static void build_command_line(struct ffmpeg_muxer *stream, struct dstr *cmd,
 		add_video_encoder_params(stream, cmd, vencoder);
 
 	if (num_tracks) {
-		dstr_cat(cmd, "aac ");
+		const char *codec = obs_encoder_get_codec(aencoders[0]);
+		dstr_cat(cmd, codec);
+		dstr_cat(cmd, " ");
 
 		for (int i = 0; i < num_tracks; i++) {
 			add_audio_encoder_params(cmd, aencoders[i]);