When the option is activated with language/track that does not exists in the source, then the option will be ignored.When the option is activated with language/track that does not exist in the source video, then the option will lead to output video with only chosen language/track (even if it means to discard all subtitle/audio from the source).the video destination folder shouldn't be the same as source folder.You can set your default so the app will remember them in the next run.
You can change subtitle/audio settings(delay, track name, language) for each subtitle/audio file to override global settings.If your muxing is limited to add/delete, or make old track default/forced, you can make it fast, a prompt will appear when this happen.You can set an old audio track to be default/forced.You can set an old subtitle track to be default/forced.You can keep audios with specific language(s) or track id(s) and discard any other audio.You can keep subtitles with specific language(s) and/or track id(s) and discard any other subtitle.You can discard old attachments files from all videos.You can reorder the chapters so that each chapter is matched with the right video.Chapters names don't have to match videos names.You can add multiple audios to each video file.You can set the new audio to be at the top of audios tracks in the output video.You can set audio delay, track name, language.You can set audios to be default/forced.You can reorder the audios so that each audio is matched with the right video.Audios names don't have to match videos names.You can add multiple subtitles to each video file.You can set the new subtitle to be at the top of subtitles tracks in the output video.You can set subtitle delay, track name, language.You can set subtitles to be default/forced.You can reorder the subtitles so that each subtitle is matched with the right video.Subtitles names don't have to match videos names.You can change default video duration/FPS.You can view media info of each file so you can keep an eye on the video tracks.App for muxing(merging) videos with with many options.