Strange sound issue ON BBC1

I use a simple HD freeview box for recording CA and promos. I've spoken to someone about this and it does seem to be a strange switch over takes place.

This switch over happens between Strictly and Doctor who, It seem to switch sound feeds changes and some players cant coupe with the switch.

VLC can do the first couple of seconds and then it drops. MPC can coupe better with after the switch.

Can anyone explain what this switch is?

Probably the switch from stereo to 5.1. Strictly and Doctor Who are both in 5.1, but the continuity between them isn't. It switches back to 5.1 at the start of the ident. You'll sometimes get a short blast of static when it switches to 5.1 because your box will typically feed your TV uncompressed PCM stereo followed by re-encoded Dolby Digital (the original stream is AAC all the way, 2.0 or 5.1) and your TV won't know what's what until it notices the change.

My VLC gets confused when the switch happens, and starts playing back at a lower pitch and with gaps, but it doesn't drop.

On my TV the sound drops really low when something is broadcast in 5.1. Does anyone else get this? I only have a Stereo cinema system connected to my TV.

I forget the details, but Dolby Digital streams have some kind of reference volume level encoded in them. I think it typically does sound much quieter if decoded without reference to that level. Maybe something in your system isn't honouring it.

I think I usually have to turn my TV quite a way up if I'm playing back a file with Dolby Digital audio (compared to one with just stereo), but when just watching BBC One HD everything typically sits around the same level, whether it's 2.0 or 5.1.

I have to do the same if I'm watching a 5.1 film on the streaming services or a DVD. As you say, the mix on DVB-T or DVB-T2 means I don't have to turn the volume up.