In the configuration, `max_duration` can be set to prevent
long song(URL item) being downloaded and added to the
playlist.
This whitelist feature provided a way to override this
duration check: songs being whitelisted will be added to
the playlist no matter how long they are.
Three admin commands are introduced:
- !urlwhitelist (!urlw)
- !urlunwhitelist, (!urlunw)
- !urlwhitelistlist, (!urlwls).
Also, if one song fails due to its length, the bot will
show the length of this song and the max length limit in
the reply message.
Implement #173, #196.
Currently, after downloading YouTube videos, FFmpeg is used to convert
the downloaded audio file into MP3 for historic reasons (there was no
database to keep the metadata around, so the ID3 tags in the MP3 file
were necessary to be able to read the metadata later on).
Now that a metadata database exists, this is no longer necessary. This
conversion is also fairly straining for slower CPUs or CPUs that do not
offer the appropriate processor extensions to be able to accelerate this
conversion, such as older ARM devices - in my case an ARMv7 32-bit
device, where the conversion could take over a minute for a fairly
simple 3-minute audio file of keeping a single core maxed out.
This should also result in less latency playing audio files on stronger
processors, though probably less noticeably.
Fixes#205
