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Monday 6 December 2004

HTPC project: Snafus

By Osma on Monday 6 December 2004, 23:31

It seems I've hit a few problems with my HTPC project that are quite annoying.

MythTV will not tune to a channel in "live TV" mode - only when recording. So it's impossible to view a channel without first programming the current show to be recorded. I'm sure this is a local config problem rather than a general error in MythTV, but it does point out a couple of annoying UI problems.

My DVB card or its driver apparently randomly decides to not receive data once in a while. Over the weekend, it meant that none of the scheduled recordings actually happened. Argh...

And finally, I can not make suspend/resume of the system work. First of all, MythTV does not seem to run the halt command (although it does warn that it will), and secondly, even if it did, the ASUS BIOS does not in fact resume the computer at the time programmed to the BIOS, regardless of whether I do this with the 'nvram-wakeup' program or via the BIOS screen.

For some reason, MythTV will lock up X in a way in which the only cure is a full reset of the computer when trying to view a DVD. Funnily enough, this is not a complete system crash, as background processes are still running and it is possible to cleanly shut down the computer (I've programmed the power button to do a 'shutdown -h'), but the console will not respond to anything. Perhaps this is an NVIDIA related issue, as I can't seem to make the XvMC video acceleration work reliably either.

Comment by oa on Tue, 07 Dec 2004 23:31:20:
Hmm. Today, viewing live tv suddenly works, at least most of the time. I believe this has something to do with mythbackend not acting very intelligently when the DVB card does not pass through a proper channel stream, as wuold happen if a channel you're trying to tune into is not transmitting. The DVD problem turned out to be a lightly documented, but apparently fairly well known "feature" of MPlayer not supporting DVD playback very well, in particular wrt DVD menus. Switching MythTV's configuration to use Xine instead fixed that issue.

Wednesday 1 December 2004

HTPC project: viewing a channel

By Osma on Wednesday 1 December 2004, 22:01

In this part, we find how random googling does not always provide the best results at first, and ultimately get the reward of live TV on screen.

Previously: our hero decides tp build a MyhTV powered HTPC to drive his video projector, buys a DVB-T receiver card and manages to make Linux recognise it. Read more after the break...

After getting over the initial confusion of lspci -v declaring that a new network device has been installed to the system, I started looking for how to access a channel. Googling turned up a document which I am not linking here as it mislead me by a couple of hours by instructing to use tools called dvbtune and dvbstream, combined with a lot of hand-written configuration. This might have worked at some point, with some hardware, but in my case, dvbstream would be able to keep the channel tuned by approximately 2 seconds, thereby replacing initial reward with frustration. Not recommended.

Fortunately, however, these instructions did mention another tool called tzap. Searching for that led to the goldmine: linuxdvb.tv's utilities, of which a Fedora-compatible RPM is also found, include dvbscan and tzap. These tools made it significantly easier to come up with a full channel listing and view a channel with a couple of commands.

First, you need to find out which transmitter your aerial antenna is pointed at. In Finland, these are documented on Digita's digitv.fi site, elsewhere you'll need to refer to some other source of information. With any luck, the dvb tools package I mentioned above will include the necessary frequency tables already, and the rest is easy:

$ scandvb /usr/share/dvb-apps/dvb-t/fi-Espoo
$ tzap Subtv -o - | mplayer -cache 1024 -

Success at last! Getting this far was perhaps 8 hours of tinkering, with lots of false starts and dead ends, but also some time spent looking at other things, which would become useful later. With the information I now have, getting here would take all of 20 minutes, including the time to install the hardware.

In the next part, some user-level discussion of how this actually works instead of all this technobabble..

Sunday 28 November 2004

Building of a digital HTPC, part 1

By Osma on Sunday 28 November 2004, 21:03

I've been thinking about this project pretty much ever since I replaced our television with a video projector last March. In the meantime, I've just been reading about the matter and thinking about alternative ways of doing it, but yesterday I got on with the job.

Plan: To build a DVB-enabled, Linux and MythTV powered HTPC to act as a DVD player, video recorder, living room entertainment system, and whatever else comes along. In this space, I'll be documenting the process, talking about the gotchas I've ran into, and how I've managed to solve them. Perhaps I'll be asking for a bit of advice as well. The instructions on the web for this are at times quite sparse, often out of date, and occasionally misleading, so hopefully this will help someone. Read on for details...

In September, I bought an Athlon XP 2500+ system with an ASUS A8N7X-VM/400 motherboard. The primary reason I bought that, instead of for example an Athlon64 system, was that I wanted a compact M/B with most things integrated to it, because I was already thinking of building this project on that system. I didn't want to get something totally overpowered for the task, but not something that I couldn't be sure would be up to the task, either. This machine has been running Fedora Core 2 since its installation until about a week ago, when I upgraded it to FC3. It was equipped with a RADEON 9600 PRO card, but in the beginning of this project, I removed that to use the integrated GeForce 4 MX, which is easily good enough for video display, and in fact thanks to NVIDIA's well-optimised drivers, possibly better for that purpose that the ATI, given that we are in a Linux environment.

Yesterday, I bought a budget DVB-T card: TechniSat AirStar 2 TV PCI. I was told it has good reception, and its form factor is one of the smaller cards, which will be good later on when I exchange the case of the PC to a HTPC case. Many of the current crop of DVB-T cards are very high, possibly too high to comfortably fit in a relatively low-profile system. This card is of the latest revision, with an included remote control and IR receiver, which makes the package pretty high value, but a bit worrying considering on Linux it has to be supported by a volunteer effort.

True enough - it turned out that though FC3's default kernel includes the DVB subsystem as modules, it did not include the correct driver for the updated frontend chip (mt352) on the card. Only the earlier revision (mt312) worked out of the box.

Fortunately, this is a problem that can be easily overcome by using the very latest (as of November 2004, anyway) DVB drivers available a the LinuxTV website. Linux kernel module installations have come a long way: it used to be that something like this would require patching, reconfiguring the entire kernel, waiting for the whole kernel compile, and ultimately a bit of anxiety, no matter how used one becomes to the routine, of whether the new kernel would even boot the machine. No more - with FC3, you don't even need the kernel sourcecode. Simply check out the dvb-kernel module, and run make in the build-2.6 subdirectory. The only (small) complication was in deciding how to replace the existing prebuilt modules with the new ones. I decided to simply copy the new ones on top of them. I could have always returned where I started from by reinstalling the kernel RPM. No need to do so - the updated drivers work like a dream.

Comment by ThornyDevil on Sun, 19 Jun 2005 16:17:18:
Thank you for this journal. I couldn't understand why I was having problems with my new AirStar 2 card using KnoppMyth - but now I know! "frontend chip (mt352) on the card. Only the earlier revision (mt312) worked out of the box. "

Comment by Osma on Sun, 19 Jun 2005 20:31:44:
Kernels since 2.6.10 (I think) include the mt352 driver by default. These days I have two of the cards in my HTPC, working very nicely together.

Saturday 3 April 2004

HTPC thoughts

By Osma on Saturday 3 April 2004, 20:44

To go with the video projector, I'm thinking of building a HTPC box running Linux/MythTV. The thing I can't figure out, not having a desktop machine to properly test things on, is what hardware I need for the job. Comments would be welcome..

What I'm thinking is a system with a big hard disk, DVB receiver card and a DVD/CD-RW drive. I want to be able to record and watch TV shows as well as DVD movies, and being able to archive stuff in MPEG-4 format to CD would not hurt. It would also be home to our music collection, which I'm encoding from CDs to Vorbis. Being able to play a game now and then would be a bonus, but since the system is going to be running Linux anyway, I do not expect to see a lot of games on it.

To do this, the system must have enough CPU power to play back DVD, DVB and/or MPEG4 content while recording a DVB stream at the same time. It must also be able to output 5.1 audio in analog format, due to my current AV receiver not having built-in AC3 decoding. On the other hand, since the picture output will be to a video projector, I do not need S-video TV out signal, standard VGA is better. At least one PCI slot is a must, even if everything is integrated, because of the DVB card.

The cheapest, and at the same time well performing option looks to be an AMD AthlonXP/Duron with an NForce2 IGP MicroATX motherboard. However, I'm worried about the power and heat output of those systems, as obviously I want the system to be quiet (passive heatsinks would be optimal).

An EPIA MII-10000 should be able to (barely?) do this as well, but it probably won't have any CPU to spare, which worries me (have I understood everything? Am I overlooking some part of the requirements?). It would, on the other hand, probably be quite a bit cooler, although in standard setup that system also has a CPU fan.

Pentium 4 is a fallback choice - most expensive, but in lower frequencies puts out less heat than Athlon. Pentium M would be ideal, except it's even more expensive, and anyway the only desktop motherboard I've located for it does not seem to be sold by anyone, anywhere. I don't want to wait for the rumored Pentium M desktop edition, either. Anyway, there is no chipset as attractive as NForce2 for Intel processors.

As for case, I'm thinking DIGN HV5 - expensive, but really cool (pictured above). Even Sanna thought it would look OK. :) This case would take pretty much any system, being able to house most ATX motherboards. Being all-aluminum, it would probably permit some advanced heatpipe solutions for replacing at least the fans needed by an EPIA system. In any case, the common SFF boxes are out of the question - I do not want this system to look like a computer.

Tuesday 23 March 2004

Tykki

By Osma on Tuesday 23 March 2004, 08:27

Kuten Sanna ehti jo kommentoimaan, ostin sit eilen videotykin. Päädyin laitteita vertailtuani Sanyo PLV-Z1:een, jonka kuvanlaatu tässä kuvakoossa oli lähes yhtä hyvä kuin puolta kalliimman Z2:n. Panasonicit putosivat finaalista erinomaisesta kuvanlaadustaan huolimatta, koska niistä puuttuu täysin asennusta helpottavat kuvansiirto-ominaisuudet.

Vielä pitää hankkia kangas, pidemmät kaapelit, ja lopulta HTPC, jotta pääsee yhteen kuvanlähteeseen ja eroon videonauhurista.

Update: On muuten vaikea löytää yli parimetrisiä virtakaapeleita. Toi tykki käyttää maadoitettua johtoa, jonka tykin pään liitin on nyt tutkimuksien jälkeen paljastunut tyypiksi IEC C5. Suomesta ei tunnu löytyvän firmaa joka voisi toimittaa näitä johtoja yhtään pidempinä - ei edes niin kutsutusti "kattavista" elektroniikan komponenttiluetteloista. Googlekaan ei ole osoittautunut kovin hyödylliseksi, näitä kaapeleita on kyllä ruvennut löytymään mutta pisin on ollut 3m. Mä tarttisin viis..

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