Does the product of a digital tuner, such as the hd homerun, require encoding on the mythbox, or is the data from the hd homerun sent encoded already?

I'm wondering if this is why recordings seem to become mangled occassionally, especially if I delete a recording or if the system tries to go get guide data.

Alternatively, is it just a buffering issue? If the mythtv box can't write the data fast enough because it's being deluged from the external tuner, the buffer fills up, and packets just get lost.

I never had issues like this with my previous setup, which was a hauppage pvr 500 dual tuner on one box, and another on a second box. I could record 4 programs at once without a problem. Even deleting recordings wouldn't affect anything.

No, the data is already encoded in MPEG-2.

You don't have it on a wireless connection, do you? The data stream is a solid 20Mbits per channel, up to 40Mbits for the two channels together. 802.11g on its best day can't handle this stream well enough to avoid dropouts.

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No. I have it on a dedicated wireless router. The only things on that router is the hd homerun, the mythtv box, and a line going to the primary router.

It's definitely the mythtv box though. I can always ruin a current recording by deleting an existing recording.

I did notice that used ram always seems to be at near capacity, which is why I've been restarting the box daily.

AMD Athlon 1800
R5E0
300 gig hd
HDHomerun
1 gig memory

Theory #1
What filesystem are you using for recording? there could be a hang or pause when deleting large files (1+GB) using ext2/3 instead of xfs...

Theory #2
You have stated in your signature that you have 1GB ram. This shouldnt be a problem, unless you have something funky or have everything turned on (web server, combined BE/frontend, and mysql using ram)... try pulling up a terminal (ssh, or xterm) and running top. You stated you are running out of ram (perhaps memory leak) and see if you can sort by memory usage. Also if your system is showing low memory, then that would cause heavy paging (swapping) and thus will hit the drive even more depending on if recording directory (theory #1) is same physical drive as system partition.

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Actually, I'm using the default km filesystem, whatever that is. It's on a single 300 gig drive.

It was working fine with 4 analog tuners (2 on an FE box and 2 on the backend) for nearly a year until I'd added the HD Homerun and started using that as the tuner instead. The only change I'd made to the BE itself (and none to the FE) was to add the extra tuners in the settings.



Yeah, it's one system upstairs that's running a combined BE/FE and one system downstairs that's just a FE. But like I said, this wasn't having problems before when I was using the same everything except without the HD Homerun.

I have top running in an ssh window, but it doesn't seem to show any single item using much memory.

Says 1032036k total, 1013960 used, 18076 free.

All but 3 items show 0% memory used.
init .1% of memory
mythfrontend 7.6% of memory
top .1% of memory.

I'm guessing it's referring to total memory, including paged, which shows as nearly 2 gig. (1,959,920k)

But even that would only be under 150m of memory.

You need to sort by Memory usage. Top by default sorts by CPU.

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"If the facts don't fit the theory, change the facts"
--Albert Einstein

Linux keeps as much data as it can in RAM. Your RAM filling up is normal. You should not need to reboot because of this. It sounds to me like your harddrive(s) or filesystem is the problem. It simply cannot keep up with the data flow. I'd recommend placing your OS on a seperate physical hard drive and changing your /myth partition to a faster filesystem such as XFS or JFS. The KnoppMyth Wiki has instructions on how to do the file system switch.

[edit] Here's a link to an explaination on how Linux uses RAM. [/edit]

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I thought the max it could be for all subchannels combined was 20mbps (18.9 I think to be exact)? The HDHR should only be forwarding one subchannel per tuner at a lower data rate, even for 1080i/5.1, no?

It's a good question. I'm not sure the HDHR filters out the subchannels at the box, or if Myth does that later. Even it if filters, the single HD 1080i stream is something over 16M bits (32M for both channels) -- it doesn't leave much room in the transport stream.

From the marketing lies used to sell 802.11 stuff, you would figure it has enough bandwidth to handle HD streams with ease. Sadly, you're lucky to get 1/3 of the advertised bandwidth in a sustained connection. (Even 1/5 might be more accurate.)

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http://en.wikipedia.org/wiki/ATSC_Standards This gives some good info on bitrates.

MythTV .21 supports the recording of all the subchannels if you happen to need them. Might be nicer for Cable users since the bitrate is higher per 6Mhz stream.

Isn't the 16Mbits/s stream for Broadcast 1080i? They use the rest of the bandwidth for weather here. I was thinking that cable compressed more to offer more channels?

Always possible, but the thing that throws me is that I didn't change the hardware or OS at all, except to add the HD Homerun. If I don't reboot, I get problems such as more frequently garbled recordings.

If I don't reboot within a week, the front end (on the fe/be) or the back end crashes, interrupting recordings.

It's possible it's the hardware if a power glitch damaged it, maybe, but I'm not sure how I could narrow it down to the hardware.

So far, to me, the symptoms indicate memory buffering problems and/or cpu utilization, which is why I asked about mpeg encoding.

I knew the pvr 500's did the encoding on the cards, but wasn't sure if encoding is being done by software now that I'm using the hd homerun.

All the HD cards that I am aware of do not encode. They take the feed directly from the antenna and dump it to a file. Essentially this keeps CPU usage low because it is similar to downloading a file.

How about your hard drive. They tend to fail. Most manufacturers have downloadable diags that will run from cd. Maybe someone can suggest some good linux HD diags?

FWIW, the HDHR only streams the subchannel(s) that Myth
requests.

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Grant

as many of you know Linux uses a lot of RAM for filesystem cache. To get a good representation of how much of the RAM usage is apps vs filesystem cache install "htop".
It is makes things much clearer for me then "top". Both are curses based so you can run it from the shell.


Dont expect to watch HDTV over 802.11g wifi. As others have said, net bandwidth over wifi is pretty low. another nice tool to check out is "bmon". Install it on your BE and check out how much bandwidth is being used when recording from the HDHR.

BTW, what kind of Ethernet HW is in the BE?? cheap Ethernet HW can use lots of CPU, depending on the logic design. If you are using ext3 vs something like XFS that can chew up CPU too. Throw in a transcoding job and you have the perfect CPU storm on the BE.