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.
Previously using EBU R128 forced the use of the bs1770gain backend.
This change adds a whitelist of backends supporting R128. When the configured
backend is in that list it will also be used for R128 calculations. Otherwise
bs1770gain is still used as a default.
This should not change the overall behaviour of the program at all, but allow
for further R128-supporting backends to be added.
When setting up bpd tests, two servers are startet: first a control server, then
bpd. Both send their assigned ports down a queue. The recipient only needs bpd's
port and thus skips the first queue entry.
Use a `multiprocessing.Queue` instead of a `multiprocessing.Value` to avoid the
manual polling/timeout handling.
TODO: Strangely Listener seems to be constructed twice. Only the second one is
used. Fix that and then remove the code working around it.
The bpd test bind a socket in order to test the protocol implementation. When
running concurrently this often resulted in an attempt to bind an already
occupied port.
By using the port number `0` we instead let the OS choose a free port. We then
have to extract it from the socket (which is handled by `bluelet`) via
`mock.patch`ing.
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.
Return a namedtuple CommandOutput(stdout, stderr) instead of just stdout from
util.command_ouput, allowing separate access to stdout and stderr.
This change is required by the ffmpeg replaygain backend (GitHub
PullRequest #3056) as ffmpeg's ebur128 filter outputs only to stderr.
