A Python script that automates the process of setting JPN audio and full ENG subtitles as default tracks for mkv files. Processes in seconds. Great for preparing a huge collection of anime series before doing a marathon watch!

• Built with Python 3
• Supports multiprocessing
• Color-coded terminal prompts

If you run this script once, you won't ever have to manually select your preferred audio and subtitle tracks for each video in your video player. Some video players like VLC Media Player on Android don't support choosing a preferred language for audio and subtitles.

This program reads all mkv files inside a directory and subdirectories. For each mkv file, mkvmerge finds what tracks are present. We look for four properties: name, number, type, and language. These properties are used to find JPN audio and full ENG subtitles and the program sets them to default tracks.

mkvpropedit "Anime S01E01.mkv" \
--edit track:2 --set flag-default=1 --set flag-forced=1 \ 
--edit track:3 --set flag-default=0 --set flag-forced=0 \
--edit track:4 --set flag-default=1 --set flag-forced=1 \
--edit track:5 --set flag-default=0 --set flag-forced=0 \

Anime S01E01.mkv
 Audio tracks:2 Subtitle tracks:2
 Track:2 Type:aud Language:jap Name:Japanese Dub
 Track:3 Type:aud Language:eng Name:English Dub
 Track:4 Type:sub Language:eng Name:English Sub
 Track:5 Type:sub Language:jap Name:Japanese Sub
Pass

• check_ffmpeg(path='ffmpeg') - This function checks if ffmpeg, mkvmerge, and mkvpropedit are present in the /ffmpeg folder. If not, FileNotFoundError is raised.
• mkv_directory() - Opens a dialog window to ask the user for the directory of mkv files. Yields a list of mkv files.
• get_mkv_tracks(mkv_file) - This function runs the mkvmerge -i command to input mkv file and returns a JSON output containing info about the tracks inside the file.
• get_tracks_count(tracks): - This function returns the number of audio and sub tracks inside an mkv file.
• set_audio_track_flag(audio_track) - This function assigns flag_default=1 for JAP AUDIO. Otherwise, flag_default=0. The variable flag_default will be used as commandline argument in mkvpropedit later.
• set_sub_track_flag(sub_track) - This function assigns flag_default=1 for ENG DIALOG SUBS. Otherwise, flag_default=0. The variable flag_default will be used as commandline argument in mkvpropedit later.
• generate_mkvpropedit_command(mkv_file, tracks) - This function adds all audio and sub tracks as commandline arguments to mkvpropedit
• yield_terminal_output(mkv_file, tracks) - This function generates a prompt message to be displayed in the terminal. Information about the tracks' flags inside the mkv file is displayed.
• change_flags(mkv_file) - This function changes the flags of audio and sub tracks inside an mkv file, specifically, JAP AUDIO and ENG DIALOGUE SUBS. It uses the functions defined above.
• measure_duration(func) - This function measures the duration of execution of the child function wrapped herein.
• begin_process(directory) - This function when called feeds each mkv files into the whole batch flag routine under multithreading.
• main() - Starts the program with asking the user for the directory of mkv files via mkv_directory() when check_ffmpeg(path='ffmpeg') passes.

• mkvmerge - Used to fetch information about the tracks embedded inside the mkv files, including name, language, track id's, and flags for 'default' and 'forced'.
• mkvpropedit - Used to edit and set the flags of the tracks of the mkv files.
• ffmpeg - Used to extract subtitle tracks from mkv files and save them in srt file format.