We have Direct and we routinely FF through commercials. For no apparent reason the FF function will sometimes stop in the middle of a commercial. And it’s usually a commercial for Direct! Have they embedded some secret code to disable the FF function or is this just some cosmic coincidence?
Moving from Cafe Society to General Questions.
I’ve had a Direct TV DVR for many years and I have never noticed this happening before. Sounds like either coincidence, or confirmation bias, but let’s see if some others have noticed it too.
Former tester here. Every time this has come up in the past, it’s been a bug and the developers have fixed it rapidly (usually for the next test build, though regular users might need to wait for the quarterly update).
The technical reasons are somewhat complex. DirecTV inserts some ads at the source, but DVRs can also insert regional / local ads by market. So the DVR is switching from a stream of recorded TV to a different recording, likely with different audio/video codecs. If you have a surround system that can display what sort of audio signal is coming in, you’ll see (for example) switches from AC3 5.1 to 2.0 when programming changes.
And, frankly, the older DVRs (HR2x up to and including HR23) really don’t have enough CPU power for what they’re being asked to do these days. The HR24 and newer units are better.
By the way, if you report the FF problem to DirecTV, they’ll want to know both the exact hardware model (HR21-700, for example) and the software version. All of these are available in System Settings/Information.
Wow, that’s cool info. I have definitely noticed the sound switch between national & local commercials. Do cable companies do this with their DVRs too? Or do they always make the switch at their regional broadcasting centers?
Another reason I’m glad I have a TiVo! 
I’ve noticed this (or a similar issue) also on my Directv Genie. What I’ve noticed is that the picture freezes during a FF, but it appears the FF does not stop. If I wait during a picture freeze, then hit run, the fast forward has advanced too far.
Nowadays, whenever I see a picture freeze, I hit run, then FF again, and the picture starts advancing again.
J.
As far as I know (I don’t have recent experience there), they do the inserts at the local / regional level. The reason DirecTV can’t do this is that they are beaming the same signal to the whole country for most channels (some local channels are on spot beams, but those are still pretty wide.)