The last two times I looked at Channel 4 HD on Freeview (DVB-T2) there was a strange problem with the audio. All the ambient sounds and background music were there but voices were very muffled. One time was a film and the other was a US drama series (Revenge). The same channel on Freesat (DVB-S2) was OK.
This was on a "remote client" using xineliboutput + vdr-sxfe with analogue stereo audio. I just tried it on my main TV (also using vdr-sxfe but connecting to VDR on localhost) with HDMI audio, and the sound was normal on that, but it was a British cookery show. I don't know yet whether the difference was because of the type of programme or the respective PC's audio settings.
I tried changing the stereo mix settings in VDR's xineliboutput plugin config, but one setting didn't do anything and the other turned it into a loud, harsh noise.
Is this just the wrong audio stream being selected (I didn't think of trying to find an alternative stream at the time) or the player discarding channels instead of downmixing into stereo?