Rockbox

This small patch is an alternative implementation of
the functionality of patch 815747. It implements
relative volume setting that can be used in config
files to change the current volume with a given
percentage. Simply prefix the value with a ‘+’ or ‘-’ sign to increase/decrease the current setting with the
desired percentage.

This is easier and more intuitive than the “rvolume” approach, but has the disadvantage that a non-patched
RockBox will interpret negative values as the minimal
setting, and positive values as absolute values.

This patch is mostly effective in conjuction with patch
750691, that implements per-file/directory/playlist
config settings. For example, if a particular track or
album is louder than average, a per-album config file
can use the rvolume setting to decrease the volume.
This is much better than having to set the volume to an
absolute value.

This patch is easy, simple, effective, and updates the
documentation as well .