* Do not warn when fixup is skipped for existing file
* [fragment] Fix `--skip-unavailable-fragments` for HTTP Errors
* [utils] write_string: Fix bug in 59f943cd50
* [utils] parse_codecs: Subtitle codec is generally referred to as `scodec`. https://github.com/yt-dlp/yt-dlp/pull/2174#discussion_r790156048
* [docs] Remove note about permissions. Closes#3597
Using https://github.com/asottile/pyupgrade
1. `__future__` imports and `coding: utf-8` were removed
2. Files were rewritten with `pyupgrade --py36-plus --keep-percent-format`
3. f-strings were cherry-picked from `pyupgrade --py36-plus`
Extractors are left untouched (except removing header) to avoid unnecessary merge conflicts
* Split `__init__` code into multiple functions
* Clean up validation code by grouping similar types of options
* Expose `parse_options` to third parties
* Move `_match_entry` and `post_extract` to `process_video_result`. It is also left in `process_info` for API compat
* `--list-...` options and `--force-write-archive` now obey filtering options
* Move `SponsorBlockPP` to `after_filter`. Closes https://github.com/yt-dlp/yt-dlp/issues/2536
* Reverts 4ec82a72bb since this commit addresses the issue it was solving
* Add option `--live-from-start` to enable downloading live videos from start
* Add key `is_from_start` in formats to identify formats (of live videos) that downloads from start
* [dash] Create protocol `http_dash_segments_generator` that allows a function to be passed instead of fragments
* [fragment] Allow multiple live dash formats to download simultaneously
* [youtube] Implement fragment re-fetching for the live dash formats
* [youtube] Re-extract dash manifest every 5 hours (manifest expires in 6hrs)
* [postprocessor/ffmpeg] Add `FFmpegFixupDuplicateMoovPP` to fixup duplicated moov atoms
Known issue: Ctrl+C doesn't work on Windows when downloading multiple formats
Closes#1521
Authored by: nao20010128nao, pukkandan