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~~NOTRANS~~

====== Audio/Video Processing and Podcasts ======

===== SoX - Sound eXchange =====

see [[https://sox.sourceforge.net/|https://sox.sourceforge.net/]]

===== FFmpeg =====

[[https://trac.ffmpeg.org/|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. [[https://qwinff.github.io/|QWinFF]]
    * source: [[https://github.com/qwinff/qwinff|https://github.com/qwinff/qwinff]]


===== YouTube Downloader =====

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 [[https://github.com/yt-dlp/yt-dlp/wiki/Forks|yt-dlp Wiki]] on 2022-09-19, there are 3 active forks for the command line:
  * [[https://github.com/ytdl-org/youtube-dl|youtube-dl]] - The original project
  * [[https://github.com/yt-dlp/yt-dlp|yt-dlp]] - a promising alternative
  * [[https://github.com/ytdl-patched/ytdl-patched|ytdl-patched]] - a fork of yt-dlp

There are a multitude of Downloader-GUIs, here a very short selection:
  * [[https://jely2002.github.io/youtube-dl-gui/|Open-Video-Downloader]]
    * abandoned source: [[https://github.com/jely2002/youtube-dl-gui|https://github.com/jely2002/youtube-dl-gui]]
    * new?: [[https://github.com/StefanLobbenmeier/youtube-dl-gui|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
    * [[https://clipgrab.org/|ClipGrab]] - the origin for this project
    * source: https://github.com/FreedomBen/clipgrab


===== Podcast programs & apps =====

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

  * [[https://antennapod.org/|AntennaPod]] for Android
    * source: https://github.com/AntennaPod/AntennaPod
  * [[https://pocketcasts.com/|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
  * [[https://gpodder.github.io/|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
      * [[https://lifehacker.com/how-to-turn-youtube-channels-into-subscribable-podcasts-496976976|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


===== Providing an own podcast feed =====

[[https://github.com/mxpv/podsync|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.


===== Changing speed - not pitch =====

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

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

[[https://trac.ffmpeg.org/|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|git://source.ffmpeg.org/ffmpeg]]

it is based on [[https://sourceforge.net/projects/apprenticevideo/|https://sourceforge.net/projects/apprenticevideo/]]\\
with code at [[https://github.com/pkoshevoy/aeyae|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|http://www.surina.net/article/time-and-pitch-scaling.html]]

===== Loudness =====

see [[https://en.wikipedia.org/wiki/EBU_R_128|EBU R 128]]

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