Merge video, audio and subtitles in one folder using ffmpeg + bash script?

[oknchm]

Hello! Need help on how to merge video, audio, and multiple subtitles from one folder using ffmpeg with bash script. I'm using Google Colab to run the script with my Drive mounted on it.

So, I have a folder on my Drive named "episode1" with the following files and want to merge them to .mkv.

episode1_video.mp4
episode1_audio.m4a
episode1_subtitle_en.vtt
episode1_subtitle_es.vtt
episode1_subtitle_pt.vtt

Merging them manually with this command:

ffmpeg -i "/content/drive/MyDrive/episode1/episode1_video.mp4" -i "/content/drive/MyDrive/episode1/episode1_audio.m4a" -i "/content/drive/MyDrive/episode1/episode1_subtitle_en.vtt" -i "/content/drive/MyDrive/episode1/episode1_subtitle_es.vtt" -i "/content/drive/MyDrive/episode1/episode1_subtitle_pt.vtt" \
-map 0:v -map 0:a? -map 1 -map 2 -map 3 -map 4 \
-c copy \
-disposition:s:0 default \
/content/drive/MyDrive/show_episode1.mkv \
-hide_banner

However, this is time-consuming since I need to copy-paste each file path manually, so I tried making a bash script. (Please note that I'm new to script-making and just mostly copied and combined what I found on the internet.)

#!/bin/bash

input_directory="/content/drive/MyDrive/episode1"  #@param {type: "string"}
output_path="/content/drive/MyDrive" #@param {type: "string"}
file_name="show_episode1" #@param {type: "string"}

for video_file in "$input_directory"/*.mp4; do
base_path=${video_file%.*}
base_name=${base_path##*/}

for audio_file in "$input_directory"/*.m4a; do
base_path=${audio_file%.*}
base_name=${base_path##*/}

for subtitle_file in "$input_directory"/*.vtt; do
base_path=${subtitle_file%.*}
base_name=${base_path##*/}

ffmpeg -i "$video_file" -i "$audio_file" -i "$subtitle_file" -map 0:v -map 0:a? -map 1 -map 2 -map 3 -map 4 -c copy -disposition:s:0 default "$output_path"/"$file_name".mkv -hide_banner

done
done
done

But I get this error instead:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/content/drive/MyDrive/episode1/episode1_video.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 1
    compatible_brands: isomavc1mp42iso5iso6
  Duration: 00:01:09.47, start: 0.066733, bitrate: 3869 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 3862 kb/s, 29.97 fps, 29.97 tbr, 30k tbn, 59.94 tbc (default)
    Metadata:
      handler_name    : Bento4 Video Handler
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from '/content/drive/MyDrive/episode1/episode1_audio.m4a':
  Metadata:
    major_brand     : isom
    minor_version   : 1
    compatible_brands: isomiso5iso6
  Duration: 00:01:09.50, start: 0.000000, bitrate: 199 kb/s
    Stream #1:0(kor): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 192 kb/s (default)
    Metadata:
      handler_name    : Bento4 Sound Handler
Input #2, webvtt, from '/content/drive/MyDrive/episode1/episode1_subtitle_en.vtt':
  Duration: N/A, bitrate: N/A
    Stream #2:0: Subtitle: webvtt
Invalid input file index: 3.

There's something wrong/missing with the script but can't figure out how to fix it. I want to merge everything including all the subtitles. Hope someone can help. Thank you!

[johns0]

Unless you want to use ffmpeg all the time under a script why not use mkvmerge?