Make your own epub with free open source LibreOffice Writer

Tools | Chapter Numbering and Paragraph Style choose Heading 2 (or 1 or 3)

Highlight each chapter then right click and choose paragraph | Heading 2 you wish to include in the Table of Contents (usally each one...just in this bible I'm doing every 5)

Quicker way is double click on chapter then use the keyboard shortcut

At the top of the document choose Insert | Table of Contents and Index | Table of Contents, Index or Bibliography

After you've made a few chapters with paragraph style of Heading 2 right click on a TOC Table of Contents and Update Index. This is invisible part of the epub just put in the Outline of the epub when you export it.

Export your epub 3.0. Add a cover jpg image, set Title and Author.

epub outline or Table of contents on eyephone

epub in dark mode on eyephone using Kybook 3

Splitting video (mp4 or mkv) into fixed intervals as chapter markers into a single mkv file.  Drag mp4 or mkv video into MKVToolNix (open source Linux, Mac, Win) into the Multiplexer | Output and choose Chapters in fixed intervals | Start Multiplexing

Chapter <NUM:2> will give Chapter 01, Chapter 02, etc. or change to <NUM:3> for Chapter 001, Chapter 002, etc. 00:15:00 or 15:00 or 15m will split audio into chapters every 15 minutes.

split video file (mp4 or mkv) into fixed intervals for each file video001.mkv, video002.mkv, etc.

splits into multiple files each 2 minutes

ffmpeg tips

ffmpeg is an open source free video encoder, muxer, audio encoder

split video into 3 min equal time interval segments split00.mp4, split01.mp4, split02.mp4, split03.mp4

ffmpeg -i input.mp4 -c copy -f segment -segment_time 3:00 -reset_timestamps 1 test%02d.mp4

-reset_timestamps 1 is critical as for each segment it recalculates the time

%02d outputs 00, 01, 02, 03, etc. change to %03 for 000, 001, 002, 003, etc.

for an hour use 1:00:00 not 60:00

ffmpeg tips
Extracts audio from a video file to an mp3  -b:a 256k - set audio bitrate (default 128kbps) -ar 44100 - Set the audio frequency of the output file.  22050, 44100, 48000 Hz. -ac 2 - Set the number of audio channels. (1 mono, 2 stereo, etc.) -vn -an -sn (skip video, audio, or subtitle stream)

ffmpeg -i input.mp4 -vn output.mp3

Extract a portion from video --ss (starting time at 6 mins) -t (time duration 4m30s) OR -to (time stop)

New video clip will be from 6 mins to 10min 30seconds mark and 4 mins and 30 seconds in length.

ffmpeg -i input.mp4 -ss 6:00 -t 4:30 output.mp4
ffmpeg -i input.mp4 -ss 6:00 -to 10:30 output.mp4

Encode a video to x265 (hevc) --crf 28 (default) 23 is better quality but bigger file size for great movies

-crf 31 is ok for a small file size
--preset medium (default) could try fast or slow but slow isn't worth the extra encoding time. Fast is about same as medium encoding time so default I believe is perfect.
-c:v  hevc (encoding to x265)
-c:v copy passthru video doesn't touch original video stream
-c:a copy passthru doesn't touch original audio stream.  
-c:s copy passthru copy subtitle stream.
-c copy will copy video, audio, subtitle streams as is (passthru)

from START of video or to END of video simply don't specify anything

ffmpeg -i input.mp4 -to 5:30 output.mp4 
ffmpeg -i input.mp4 -ss 6:32 output.mp4

encode clip from START of movie to 5 min 30 sec mark (to indicate START don't specify -ss)
encode clip from 6 min 32 sec mark till END of video (to indicated END time don't specify -to)

This section assumes ffmpeg -i input.mkv and output.mkv or mp4, etc.

-c:v hevc -c:a copy

-acodec aac (most common one)
-acodec libopus (prefer opus at 32kbps for talking only and 96kbps for movies and music)

-c:v hevc -c:a libopus -b:a 32k
 -c:v hevc -c:a aac -b:a 64k

resolution 3840:2160, 1920:1080, 1280:720, 854 or 720:480, 640:360, 426:240 (16:9 aspect ratios) to preserve aspect ratio while downscaling resolution or upscaling resolution use -2 value
-vf scale=-2:640 will downscale 1060x720 to 640p and maintain its aspect ratio

To concat files together make a text file with your videos putting file before them. Put # in front of them if not used. Makes modifying list easy.

# videos.txt file '01.mp4' file '02.mp4' file '03.mp4' file '04.mp4' file '05.mp4' #file '06.mp4' #file '07.mp4'

or use this command to generate the text file

for f in *.mp4; do echo "file '$f'" >> videos.txt; done

concat without re-encoding (make sure all have same aspect ratio, resolution, video and audio codec

ffmpeg -f concat -i videos.txt -c copy output.mp4

To re-encode video and audio

ffmpeg -f concat -i videos.txt -c:v hevc -c:a libopus -b:a 64k output.mp4

To replace original audio track with a new one

ffmpeg -i video.mp4 -i audio.wav -map 0:v -map 1:a -c:v hevc -vf scale="-2:720" -c:a copy -ss 1:17 -to 4:16 output.mp4

sets the audio track to start at 1:17 and end at 4:16.

ffmpeg -i input.mp4 -i newaudio.opus -map 0:v -map 1:a -c:v copy -c:a copy -shortest output.mp4

-shortest option sets video and audio track to the same duration determined by the shortest one.

To add an additional audio track (-map 0 chooses all streams rather than -map 0:v)

ffmpeg -i video.mkv -i audio.mp3 -map 0 -map 1:a -c:v copy -c:a copy -shortest output.mkv