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The problem: I am trying to record TV using a Toshiba Satellite Pro (2GHz, dual core, 4GB RAM, 250GB SSD, W7/32 SP1, PCTV 292e USB receiver, Argus TV recording s/w), but am having recording dropouts, which look as though the stream from the receiver is not being serviced fast enough, and consequently losing packets. Nothing is running except the recording s/w which just writes to disk. Typically 10%+ CPU usage. Doesn't seem overstretched.

I have found

  • Killing of other tasks (windows update etc) makes no difference
  • Different recording s/w and USB receiver makes no difference
  • The aerial signal is good
  • Very oddly, if some other video program, eg Video LAN sitting idle, or even a webpage with a video window in it, is running, recordings are perfect

Watching CPU speed with CPU-Z it varies between 797MHz and 2100MHz. This also true with s/w as in the last point above running.

If I then change minimum processor state in the power options (balanced plan) to 100% (was 5%), it is OK again, even without Video LAN etc running. The CPU speed then sticks at 2100MHz. (Actually above 75% appears to be sufficient).

However, that is obviously not what Video LAN etc are doing, because with them running and the standard balanced plan, records are still good AND CPU is varying from 797-2100MHz.

So, my questions are these:

  • What is it that Video LAN etc could doing in terms of changing system state programmatically that provides sufficient responsiveness for TV program recording. (I'm a software engineer, am thinking of a little app that detects recording in progress, makes system changes, detects end of recording, changes them back).
  • If I cannot find out, how safe is it temperaturewise, especially on a laptop, to keep the minimum processor state stuck at 100% (power consumption is not an issue, it is on mains power). What is max safe CPU temp?

MORE INFO:

Now found that using a different power option as above makes it a lot better, but there is still occasional breakup. The only guaranteed fix is Video LAN or similar running in the background.

So what I am really after is suggestions as to what machine settings might be being altered by Video LAN when it runs.

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  • I would give another tv/recording software a try. With digital TV there is no transcoding involved in recording, just dumping what tuner receives to disk so low CPU usage is normal.
    – lex
    Commented Oct 17, 2015 at 9:35
  • Yes, I've tried that - 3 different software suites in fact, and 2 different USB receivers! All behave pretty similarly. I would assume that the USB receivers have limited buffering and thus need servicing pretty promptly, and that is what is sometimes not happening, hence lost packets / dropouts. I therefore need to configure the machine for maximum responsiveness.
    – nmw01223
    Commented Oct 17, 2015 at 11:23
  • Possibly 2x2GHz is quite slow for recording large resolution image..
    – Croll
    Commented Oct 17, 2015 at 17:53
  • Maybe, but I don't think so. In terms of dropouts, SD and HD recordings are little different, the free CPU is OK, and it is quite capable of recording and displaying the stream at the same time, which is much more load than just recording - which is where the problem is. Anyway, it does do it fine, but only when Video LAN or similar is running. So it must be able to do it, but there's something necessary in system configuration.
    – nmw01223
    Commented Oct 18, 2015 at 12:37

1 Answer 1

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Think I have found an answer. Windows timer resolution. As standard it is set to 15.6mS, though programmatically it can be changed. Video LAN sets it to 5mS, other programs also change it (Kodi 1mS, Firefox 1mS for example).

If any of those programs are running, recordings are good, if not, bad.

As a test, wrote a dialog app to toggle the timer resolution between 15.6mS and 1mS. Every time it was bad at 15.6mS, good at 1mS.

So, I think that is the cause. Probably the USB receivers (or some buffer) are polled and the resolution isn't good enough to guarantee polling regularly enough. The full answer therefore is for the recording s/w to up the resolution while recording, the workround is to make sure something that does up it is running in the background.

A 1mS timer resolution is slight overhead (power and CPU), but necessary in this case. Though possibly less than 1mS would suffice - Video LAN does the job at 5mS.

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