DVB tunner frequency isn't getting set by NextPVR

[alvinhochun]

Hi, I am running NextPVR on Windows 7 x64 with this DCDTV350 DTMB (presented as a DVB-T device "USB 2875 Device").
I should state that I can open the device with VLC media player and view broadcasts successfully.
It does work with NextPVR too... sort of.

The problem with NextPVR is that it does not seem to switch the tuner frequency at all. First use of NextPVR on the device gets nothing on channel scan.
However, if I opened the device with VLC and let VLC set the tuner to a specific frequency with channels, NextPVR will then happily scan whatever channels on the frequency that VLC just used, but not the one set on manual scan with NextPVR.

By switching between NextPVR and VLC, I got the channels of two frequencies scanned within NextPVR. However I still need to open VLC to switch the frequency before getting NextPVR to open the correct channel (if I choose a channel on another frequency directly within NextPVR, it gets nothing.)

From `ndigitalhost-20.log`, these seems to be the key:

Code:

2016-01-10 00:51:41.331    [DEBUG][36]    DigitalRecorderDVBT::Tune@1
2016-01-10 00:51:41.331    [DEBUG][36]    DigitalRecorderDVBT::Tune@2
2016-01-10 00:51:41.331    [DEBUG][36]    DigitalRecorderDVBT::Tune@3
2016-01-10 00:51:41.331    [DEBUG][36]    DigitalRecorderDVBT::Tune@4
2016-01-10 00:51:41.339    [DEBUG][36]    DigitalRecorderDVBT::Tune@5
2016-01-10 00:51:41.339    [DEBUG][36]    Unexpected error on DVB-T put_TunerRequest: 0x80070057
2016-01-10 00:51:41.339    [DEBUG][36]    DigitalRecorderDVBT::Tune@post
2016-01-10 00:51:41.339    [DEBUG][36]    whoosh whoosh
2016-01-10 00:51:41.354    [DEBUG][36]    Calling LockChannel()
2016-01-10 00:51:41.400    [DEBUG][36]    locked=1, present=1, strength=0, quality=0   (took 47ms to check)

FYI, the frequency is set to 586,000kHz using VLC before this session.

For reference, I've also attached the log of VLC opening the tuner device and playing from it.

Any idea why VLC can set the tuner frequency but NextPVR can't?

[sub]

NextPVR treats all DVB-T devices exactly the same. It sounds like there is something quirky about this specific device's drivers, that makes it behave differently to other devices. I'd have no idea what I should be doing differently for this device.

All I can really suggest is looking for a different version of the driver, and hopefully it'll behave more like other devices.

[alvinhochun]

NextPVR treats all DVB-T devices exactly the same. It sounds like there is something quirky about this specific device's drivers, that makes it behave differently to other devices. I'd have no idea what I should be doing differently for this device.

All I can really suggest is looking for a different version of the driver, and hopefully it'll behave more like other devices.

Well, this is an old tuner that it's difficult to even find a working driver for it actually.

I was wondering if there are any other devices which experience this issue, but from what you said it sounds like there isn't. It just doesn't really make sense to me that VLC can set the tuner frequency while NextPVR can't. Perhaps there is something in VLC that is missing in NextPVR and this particular driver is upset to it? Isn't 0x80070057 the code for E_INVALIDARG?

I understand you may not want to debug a device-specific issue and add a workaround in NextPVR's codebase just for this particular device and driver... too bad NextPVR isn't opensource.

Anyway, I am still curious and I will try to see if I can find the issue without the source code... and I'll let you know if I did (though I don't have much confidence in it.) It's fine if this won't get fixed. I just want to know the cause to the problem.

[sub]

I was wondering if there are any other devices which experience this issue, but from what you said it sounds like there isn't.

I'm not aware of any.

It just doesn't really make sense to me that VLC can set the tuner frequency while NextPVR can't. Perhaps there is something in VLC that is missing in NextPVR and this particular driver is upset to it?

VLC and NextPVR will be doing largely the same thing for tuning. We could easily be doing calls in a slightly different order or something though, and maybe some bug in the driver doesn't like the order NextPVR does things or something similar.

Isn't 0x80070057 the code for E_INVALIDARG?

Yes it is, but these same args are working for everyone else, so I'm not sure what argument would be invalid. For DVB-T tuning there is pretty much only two parameters, frequency and bandwidth.

[alvinhochun]

Problem solved. I finally found a "trojan-embedded" newer version of the driver. Installed it and NextPVR now works with the device.

I guess I will never solve the mystery of the buggy driver. Thanks anyway.

For reference in case if anyone else with this tuner looking for a driver stumbled upon this post, I found the driver on hxxp://www.empiatech.com/wp/download-2/
Instead of running the setup program, you should extract the contents from Data1.cab, delete install.exe, and install the driver from within Device Manager directly.