The element downstream of mp3enc might only accept certain sample rates or channels,
make sure we relay any restrictions that do exist to upstream when it does a
get_caps() on the sink pad. That way upstream elements like audioresample or
audioconvert can pick a sample rate / channel configuration that will be accepted,
instead of just negotiating to the highest, which might then be rejected.
https://bugzilla.gnome.org/show_bug.cgi?id=641151
lame's 'lgv' variable is only initialized when the caps
is negotiated, whenever a seek happens before that, it would
attempt to call a function on an empty pointer, causing the crash.
Fixes#603515
lame_set_VBR_quality(), which takes a floating point value for the
quality, has been added only in v3.98. Use lame_set_VBR_q(), which
takes quality as an integer, for older LAME versions.
Fixes#581341.
