Today I received the following from my daily emerge --update

!!! One of the following packages is required to complete your request:
- media-libs/libass-0.9.11 (Change USE: +enca)
- media-video/mplayer-1.0_rc4_p20101107 (Change USE: -enca)

The instructions are clear enough, but how do I chose which alternative
to apply?

In use.local.desc I find for both entries
media-libs/libass:enca - Enables support for charset discovery and conversion.

So I guess the default is for mplayer to have that support and libass to
not have it. But I am not sure what it is. As far as I know I don't
have many charsets. My locale.gen is just

en_US ISO-8859-1
en_US.UTF-8 UTF-8

Any advice as to whether I should enable or disable the support would be
appreciated.

thanks,
allan