PPVID: Post Processing Video Lectures

PPVID is a collection of command line tools for processing recorded video lectures. These tools

• speed up the silent parts of a video,
• master the audio of a video to match that of a reference file and
• converts a video to a format suitable for web.

Though I believe that these tools may prove useful to others, they were developed to match my personal workflow.

Installation

The recommended method of installation is via pipx:

pipx install git+https://github.com/sjvrensburg/ppvid

Short Description of Tools

speed_up

The command speed_up provides a slimmed down front-end to the unsilence package.

master_video

The command master_video uses the matchering package to process your video's audio to have the same RMS, FR, peak amplitude and stereo width as the reference track.

convert4lecture

Re-encodes a video for distribution to students via online learning platforms (e.g., Moodle). Settings are subjective, but appear to work well when videos consist primarily of slides+audio.

Usage

Take the video file in.mkv and create the video out.mkv where the silent parts playback 250% faster. Define silent sections as sections where the volume is lower than -37.5 dB and longer than 0.75 seconds in duration. Note that this also works with other video formats.

speed_up -s 2.5 -v -37.5 -d 0.75 in.mkv out.mkv

Process the audio of in.mkv to have the same RMS, FR, peak amplitude and stereo width as the reference audio file reference.wav. Will produce a video in_mastered.mkv. Note that this also works with other video formats. It is, however, required that the reference audio is a wave file.

master_video in.mkv reference.wav

Convert in.mkv to an MP4 file that is suitable for viewing in most browsers. Set the CRF to 28 and use ffmpeg's slow preset. This produces a file named in_converted.mp4.

convert4lecture -c 28 -p "slow" in.mkv

FAQ

Why should I use this if unsilence, matchering and ffmpeg can already do all of this?

You're right, you can and you should. As already stated, PPVID merely provides a frontend to the tools. The options and terminology used here suits my personal needs.

Does it work on Windows?

In theory, if ffmpeg is in your PATH then it should work. However, I have not tested this.

How are you using this?

With COVID, I've been working from home and recording lectures there. My lectures are simply me reading my slides and demonstrating the use of software. I speak quite slowly with a lot of pauses. Removing these pauses in post-production is a pain, hence the speed_up.

Typically, after recording in OBS, I listen to my recording at 2x speed. I make notes about errors or sections that I need to cut out, ignoring the previously mentioned pauses. I use shotcut to quickly remove those errors. Thereafter, I apply speed_up.

I use master_video to ensure that the sound of my lectures are consistent from one video to the next. This is necessary since the placement of my microphone, tone of my voice, etc. changes between recordings.

Finally, speed_up and master_video should be applied to high-quality videos prior to any aggressive compression. However, due to file size limits and out of consideration for our students, compression is necessary. Therefore, as a final step, I run convert4lecture.

Acknowledgements

These tools would not exist without the following packages:

• unsilence,
• matchering and
• ffmpeg-python.

Many thanks to the developers of those packages.