Question Video slowly loses sync with audio

[David Taber]

Hi everyone,

Like a lot of folks, I've had the problem of video and audio falling out of sync with all sources and players, except VLC, which for some reason has been immune. Related symptoms included a lot of stuttering, particularly if I had iTunes playing and loaded a complex page in Firefox. I'm running pretty much "stock" everything on a fast laptop, with the K-lite codec set. Tried all the usual solution tactics, including the "play audio problems" troubleshooter, to no avail.

Discovered the "disable fast boot" trick and it seems to solve the problem. Yay. We'll see how long it lasts.

So now my question: why on earth does this fix the problem? I'd like to understand the mechanism, so if the problem recurs (and the disable-fast-boot doesn't work) I have a place to start troubleshooting.

I'm guessing that the fast boot feature (which only affects cold start of the system...go figure) does some real-time housekeeping (like it's counting driver interrupts or something). What's strange is this symptom only affects certain hardware configurations -- I have another win10 laptop that's much slower yet it has never had an audio/video sync problem.

 

[LinuxDevice]

I can't answer, but this does bring up some interesting questions which might help in the end.

First, how much content is stored locally, versus how much of the problem content is Internet? I suspect you already have considered the Internet, but I have to ask. There is also a more subtle side of this question even for local content: Many applications are set to access the Internet for information about that content (sometimes for extra information, sometimes for DRM). If you boot without Internet (e.g., physically unplug the wired ethernet or disable WiFi), does anything change? In particular, vlc-player has an ability to be set to not use the Internet to find extra information.

Second, I have a very bad theory about something which might change depending on fast boot or no fast boot. Sometimes temperatures and power loads get more of a chance to stabilize if not using fast boot.

Related to this, but probably not really participating in the problem, RAM goes through "training" during boot. Training basically tries a number of different clocking configurations and picks the best result before booting continues. There might be some conditions which trigger training (I work on embedded systems, not x86), and I doubt fast boot has time to do so. Perhaps something is triggering better RAM timings for the longer boot case (without fast boot). To this extent, you could possibly do a CMOS reset, verify your RAM is running at full speed, and then test again.

If something is using up too much RAM, and swapping starts occurring, then I suspect latencies would get worse and worse. You might want to bring up task manager and see what RAM and CPU use differences are during better or worse conditions.

If you are running all video and audio decoding over CPU, then CPU load will matter a lot, and things may not be too stable at different loads or with different media. If instead you are using GPU decoding, then your ability to process heavier loads without stuttering will become much better. I have no idea if this K-lite CODEC is even capable of using GPU or not, but vlc-player probably defaults to a CODEC which can offload to the GPU. Task manager does have a GPU load display available, so you might compare "good" versus "bad" while observing GPU changes.