DOCS/interface-changes.rst: adjust some audio filter change notes

The first change is about spdif - I mostly ignore spdif issues these
days, but it seems like the recent changes made handling of it slightly
better (but I didn't really test).

The second change is about broken libavfilter filters. We won't restore
the old behavior, because people were complaining about the old behavior
in the past. Possibly we could make libavfilter export this was metadata
and use the old behavior if we know they're broken - but it doesn't
exist yet.

DOCS/interface-changes.rst

@@ -58,15 +58,17 @@ Interface changes
           between PCM and AC3 output, the audio output won't be reconfigured,
           and audio playback will fail due to libswresample being unable to
           convert between PCM and AC3 (Note: the responsible developer didn't
-          give a shit)
-        - inserting a filter that changes the output channel layout will not
+          give a shit. Later changes might have improved or worsened this.)
+        - inserting a filter that changes the output sample format will not
           reconfigure the AO - you need to run an additional "ao-reload"
           command to force this if you want that
         - using "strong" gapless audio (--gapless-audio=yes) can fail if the
           audio formats are not convertible (such as switching between PCM and
           AC3 passthrough)
         - if filters do not pass through PTS values correctly, A/V sync can
-          result over time
+          result over time. Some libavfilter filters are known to be affected by
+          this, such as af_loudnorm, which can desync over time, depending on
+          how the audio track was muxed.
     - remove out-format sub-parameter from "format" audio filter (no replacement)
     - --lavfi-complex now requires uniquely named filter pads. In addition,
       unconnected filter pads are not allowed anymore (that means every filter