see https://sox.sourceforge.net/

FFmpeg provides many audio processing filters:

• https://trac.ffmpeg.org/wiki/AudioChannelManipulation
• https://trac.ffmpeg.org/wiki/AudioVolume
  • https://github.com/slhck/ffmpeg-normalize
• https://trac.ffmpeg.org/wiki/How%20to%20speed%20up%20/%20slow%20down%20a%20video

latest prebuilt (static) binaries:

• https://github.com/BtbN/FFmpeg-Builds/releases

FFmpeg is utilized in several tools, e.g.:

• in (YouTube) Downloader GUIs
• Audio/Video format and CODEC conversion, e.g. QWinFF
  • source: https://github.com/qwinff/qwinff

Downloading audio and video files is interesting for archiving - but also preprocessing for later watching or listening. Many platforms - other than YouTube - are supported.

As described in yt-dlp Wiki on 2022-09-19, there are 3 active forks for the command line:

• youtube-dl - The original project
• yt-dlp - a promising alternative
• ytdl-patched - a fork of yt-dlp

There are a multitude of Downloader-GUIs, here a very short selection:

• Open-Video-Downloader
  • abandoned source: https://github.com/jely2002/youtube-dl-gui
  • new?: https://github.com/StefanLobbenmeier/youtube-dl-gui
• ClipGrab - a GUI for (YouTube-)Downloader (and converter)
  • source and linux releases with my modifications
    • https://github.com/hayguen/clipgrab
  • ClipGrab - the origin for this project
  • source: https://github.com/FreedomBen/clipgrab

Podcast apps (automatically) download episodes from RSS feeds for (offline and mobile) listening.

• AntennaPod for Android
  • source: https://github.com/AntennaPod/AntennaPod
• Pocket Casts for Android, iOS and Web (for Linux or Windows PCs)
  • free version doesn't allow entering a (private) Feed URL
  • don't know if commercial Plus allows Feed URLs
• gPodder for Windows/Linux/MacOS computers
  • source: https://github.com/gpodder/gpodder
  • more downloader and UI than player
  • also allows downloading/watching videos from YouTube channels. that requires a special URL with the channel-id:
    • https://commentpicker.com/youtube-channel-id.php
    • https://stackoverflow.com/questions/14366648/how-can-i-get-a-channel-id-from-youtube
    • LifeHacker Turn YouTube channels into Podcasts does no longer work, but shows the idea
  • selected gPodder docs
    • https://gpodder.github.io/docs/time-stretching.html
    • https://gpodder.github.io/docs/extensions/youtubedl.html
    • https://gpodder.github.io/docs/extensions.html

Podsync can download videos, convert to audio and publish them as an RSS feed - suitable for subscription with podcasts apps. Tools like yt-dlp and ffmpeg are utilized. The only downside: Podsync requires a public server.

Listening consumes time - of course. Despite skipping (silent) sections, many episodes can be perceived at (much) higher speed - depending on the speaker(s); thus saving time. The following points to some programs/algorithms.

TDHS, see https://en.wikipedia.org/wiki/Time-domain_harmonic_scaling
implementation: https://github.com/hayguen/audio-stretch
and it's origin https://github.com/dbry/audio-stretch

Browser Extension: skip-silence
https://github.com/vantezzen/skip-silence/issues/36
https://chrome.google.com/webstore/detail/skip-silence/fhdmkhbefcbhakffdihhceaklaigdllh?hl=en

FFmpeg uses atempo:
https://trac.ffmpeg.org/wiki/How%20to%20speed%20up%20/%20slow%20down%20a%20video

libavfilter/af_atempo.c in git://source.ffmpeg.org/ffmpeg

it is based on https://sourceforge.net/projects/apprenticevideo/
with code at https://github.com/pkoshevoy/aeyae
in yae/ffmpeg/yae_audio_tempo_filter.h

theory at http://www.surina.net/article/time-and-pitch-scaling.html

see EBU R 128

https://github.com/hayguen/loudness-scanner
origin https://github.com/jiixyj/loudness-scanner