This commit mostly addresses feedback:
- remove some unused parenthesis
- fix a typo
- expand some docstrings
- document that ffmpeg is usually easy to install
Add replaygain backend using ffmpeg's ebur128 filter.
The album gain is calculated as the mean of all BS.1770 gating block powers.
Besides differences in gating block offset, this should be equivalent to a
BS.1770 analysis of a proper concatenation of all tracks.
Just calculating the mean of all track gains (as implemented by the bs1770gain
backend) yields incorrect results as that would:
- completely ignore track lengths
- just using length in seconds won't work either (e.g. BS.1770 ignores
passages below a threshold)
- take the mean of track loudness, not power
When using the ffmpeg replaygain backend to create R128_*_GAIN tags, the
targetlevel will be set to -23 LUFS. GitHub PullRequest #3065 will make this
configurable.
It will also skip peak calculation, as there is no R128_*_PEAK tag.
It is checked if the libavfilter library supports replaygain calculation. Before
version 6.67.100 that did require the `--enable-libebur128` compile-time-option,
after that the ebur128 library is included in libavfilter itself. Thus we
require either a recent enough libavfilter version or the `--enable-libebur128`
option.
After commit `30395911 util.command_output: return stderr, too`,
`command_output` returns a tuple of stdout and stderr. Document that change by
adding a changelog entry and add a usage note to `command_output`'s docstring.
*All* URLs were checked manually, but only once per domain!
I mostly concerned myself with URLs in documentation rather than source
code because the latter may or may not have impactful changes, while the
former should be straight forward.
Changes in addition to simply adding an s:
- changed pip and pypi references as their location has changed
- MPoD (iOS app) url redirects to Regelian, so I replaced those
- updated homebrew references
Notable observations:
- beets.io does have HTTPS set up properly (via gh-pages)
- beatport.py uses the old HTTP url for beatport
- as does lyrics.py for lyrics.wikia.com
- https://tomahawk-player.org/ expired long ago, but the http page
redirects to https regardless
- none of the sourceforge subdomains have https (in 2019!)
