Ongoing My HTPC - Some Good News, Some Bad... (1 Viewer)

[madmonkeyman]

Hello,

I had a quick scan on the net for your DVB-T card and I've got a funny feeling that it does not have a hardware MPEG decoder and will be using a software decoder which will cause the CPU to take on the task of decoding hence the high CPU.

You could buy a DVB-T card that has a hardware decoder onboard and it will then do all the decoding for you. My LifeView card has a hardware decoder and the CPU time when watching tv sits at around 10-15%ish.

Monkey.

 

[Elf]

Monkey,
Thanks for your reply, you're right when you say my TV card has no hardware encoder - it's a pure DVB and my understanding is that hardware encode is not necessary for a DVB signal because the signal is in MPEG2 format already (?). (Your Lifeview Duo has an analogue as well as a digital tuner, the hardware encoder will be for the analogue stream.)

The hardware decode I'm referring to is the opposite way round - the turning of the MPEG stream back into images so I can watch the TV! This should be performed, or at least assisted by my nVidia graphics card to take the stress off the CPU.

 

[madmonkeyman]

Hi Elf,

My LifeView has a hardware decoder for the DVB-T signal and a software decoder for the analogue signal. I have used a USB DVB-T only device in the past that had a software decoder and the CPU went through the roof.

I'm no expert in the decode/encode world though, so if someone else wants to step in that would be nice ;-)

Monkey.

 

[Paranoid Delusion]

All DVB-T cards do NOT stress out CPU as there is no encoding going on.

It is purely the created image that's why a reasonable graphics card is a must.

Elf

if you are getting such high cpu readings, might be a software corruption, MP or otherwise that is freaking out your system.
Might be worth a reformat and install afresh to see if this helps.
MP running with tv/timeshifting on runs between 18-25% cpu usage for me.

Best Wishes

 

[madmonkeyman]

I sit corrected!

Can someone explain to me why DVB-T cards with hardware tuners need a processor spec lower than their software tuner counterparts?? Is this more to do with them having MPEG accelleration? Also, if there is no impact on CPU then why ship them with hardware tuners at all??

Sorry for the stupid questions but I've been basing my buying strategy on whether the USB/PCI card has a hardware tuner/decoder/encoder (delete where applicable). Is there something else I should be looking at?

Monkey.

 

[Elf]

Ray, Thanks - Looks like a reinstall for me, then!

Monkey,
A normal analogue signal can go straight to your TV via the antenna, but if that signal comes into your computer it has to be converted to digital to be usable or stored on your hard drive. Your TV card will perform that conversion to raw digital, but the amount of information in video data is immense and so is normally then compressed, usually into MPEG2 format. This compression takes quite a bit of processing power to perform in real-time, and would take a decent CPU and work it quite hard. Doing it that way is commonly called "software encoding" and that's why the CPU spec for use with such cards is higher. Of course, a lot of analogue TV cards boast a hardware MPEG2 encoder. These cards automatically convert the signal to MPEG2 before suppling it to your PC, so there's no need for the CPU to get involved.

A DVB-T signal is a digital signal in MPEG2 format already. All a DVB-T TV card has to do is read the signal and supply it to your computer. There is no MPEG2 encoding required as the signal is MPEG2 already.

Once you have your MPEG2 file/stream you watch it by rendering the MPEG2 data as moving pictures and sound on your monitor/TV. This requires the compressed MPEG2 data to be decoded first - a job just as intensive as encoding it in the first place. Thankfully most decent graphics cards have built-in hardware MPEG2 decoders and will take-over or assist the process, otherwise it also has to be done by your CPU.


Whatever jobs the hardware on a DVB-T card does, MPEG2 encoding is not one of them! I think it's just a case of some manufacturers confusing things by claiming their DVB cards have hardware encoders - I suppose they're trying to say there will be no CPU usage, but really they should say there is no encoding done at all (?)

 

[madmonkeyman]

Hi Elf,

Thanks for the explanation. I've never dug too deeply into this before and that was very interesting!!

Monkey.

 

[Marcusb]

Off topic, have you done the tweaks suggested in the Tips and Tricks forum?
If your gfx card is AGP then there is a tweak to help performance there.

Have you checked the PureVideo codec to see if it is using the hardware accelleration? Not sure exactly, but I remember that there is an option somewhere. Maybe this is turned off?

 

[Elf]

Hi Marcus,
Yes I've been through all the tweaks, and the PureVideo codec has the hardware acceleration option turned on!

I have discovered a BIOS setting that increases the urgency of the fan speed response to increases in temperature. This seems to have kept the overheating under control at least, although I'm still curious about the CPU usage!

 

[Efros]

Have a look in task manger and see what process is taking all this cpu time. There have been issues reported with hi cpu usage associated with graphic animation http://www.testteam-mediaportal.com/Joomla/forum/archive/index.php/t-490.html

Hope you get it fixed.