Join Multiple Videos for YouTube (with chapters)

join-multiple-vids-for-youtube.md

Video Concatenation Guide with FFmpeg

This guide provides instructions on how to concatenate multiple video files using FFmpeg, add a black screen between each video, and address common timestamp issues during the concatenation process.

Requirements

• FFmpeg installed on your system.
• Videos to be concatenated should be in the same codec, resolution, and frame rate.

Steps

Step 1: Create a Black Screen Video

Ensure the black screen video matches the resolution and frame rate of your other videos.

ffmpeg -f lavfi -i color=c=black:s=1920x1080:r=30:d=1 black.mp4

Step 2: Create a Concatenation File

Create a text file (filelist.txt) listing all the video files to be concatenated, including the black screen video between each main video.

file 'VID_20240203_103925.mp4'
file 'black.mp4'
file 'VID_20240203_105117.mp4'
file 'black.mp4'
...
file 'VID_20240204_142836.mp4'

Step 3: Concatenate Videos Without Re-encoding

Use the following FFmpeg command to concatenate the videos without re-encoding:

ffmpeg -f concat -safe 0 -i filelist.txt -c copy output.mp4

Addressing Non-monotonic DTS Errors

If you encounter "Non-monotonic DTS" errors, use the following commands to fix the timestamps:

1. Convert each video to MPEG-TS format:

   ffmpeg -i input.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate1.ts

2. Concatenate TS files:

   ffmpeg -i "concat:intermediate1.ts|intermediate2.ts|...|intermediateN.ts" -c copy -bsf:a aac_adtstoasc output.mp4

Step 4: Generate Timestamps for YouTube Chapters

To generate timestamps for YouTube chapters:

Calculate the start time for each video manually or using the script attached, accounting for the duration of each video and the 1-second black screens. Include these timestamps in your YouTube video description, formatted as follows:

00:00:00 Introduction
00:00:10 Chapter 1
00:05:15 Chapter 2
...

Conclusion

This method ensures that videos are concatenated with a uniform format, maintaining quality and ensuring proper playback without timestamp errors.

script-to-generate-time-stamps.sh

#!/bin/bash

########################################
# This bash script reads each video file
# calculates the cumulative duration,
# and generates the timestamps for
# YouTube chapters:
########################################

# Initialize total_duration in seconds
total_duration=0

# Print the initial chapter
echo "00:00:00 Introduction"

# Loop through each video file except the last
for file in *.mp4; do
  # Get the duration of the current video in seconds
  duration=$(ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 "$file")
  duration=${duration%.*} # Convert to integer (drop decimal part)

  # Add duration of the current video to the total duration
  total_duration=$((total_duration + duration))

  # Print the next chapter start time
  printf "%02d:%02d:%02d Next Chapter\n" $((total_duration / 3600)) $(((total_duration / 60) % 60)) $((total_duration % 60))

  # Add 1 second for the black screen
  total_duration=$((total_duration + 1))
done