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Wireless network with hdtv
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Author:  mschlott [ Wed Feb 15, 2006 9:32 am ]
Post subject:  Wireless network with hdtv
I'm experimenting with a PVR-150 before going HD. One thing I'm having trouble working out, is pauses in video over my wireless connection.

Before waste too much time, I want to make sure others have done this and are happy with the results.

Is anyone using a wireless network to feed a remote front end with HD?

If so, what recording profiles are you using? What resolution, and bitrate? These may not be valid questions for HD unless you are transcoding, forgive me, I have not messed with HD yet.

What network card and router are you using?

Do you ever have problems where the front end pauses due to waiting on data to be buffered?
Author:  marc.aronson [ Wed Feb 15, 2006 11:02 pm ]
Post subject: 
I haven't tried this, but here's some data that might help. 802.11g will sustaing 18mbits -> 19mbits/second throughput. HDTV records at 19mbps, so standard 802.11g won't work. SuperG might work, but I suspect it will be problematic given the way wireless signal strenght tends to flucuate.

Marc
Author:  ed3120 [ Thu Feb 16, 2006 12:20 am ]
Post subject: 
I can't run a 720p or 1080i video from another machine across my wired 100MBps network. The video will run for 10 seconds or so, and then drop out. I only have 3 machines total on this network, so there is nothing else tying up my bandwidth. The pipe just isn't big enough to sustain the dataflow for more than a few seconds.

Remember, wireless has much more overhead than wired, you are lucky if you actually get 15 Mbps out of a 54 Mbps connection. If you want to start streaming HD from another box, you definitely have to go wired.
Author:  marc.aronson [ Thu Feb 16, 2006 12:30 am ]
Post subject: 
ed3120:

I was able to play 720p across my wired network w/ out problems. 1080i the prolems you described, but I solved this by re-configuring my front-end into a slave back end. Seems like NFS is able to move the bits over the network more efficiently than myth.

I did find that I had to replace my old P3-500mhz master backend wiht a higher-end system. It wasn't maxed out on CPU so I'm not sure where the bottleneck was...

Marc
Author:  Xsecrets [ Thu Feb 16, 2006 7:14 am ]
Post subject: 
Quote:
I can't run a 720p or 1080i video from another machine across my wired 100MBps network.


sounds like a problem with your network or maybe your NIC drivers don't know, but I can assure you a 100mbps network can handle hdtv data rates, even 1080p if you wanted, at least as long as you have good gear. you should be able to easily put 50+mbps.
Author:  mschlott [ Thu Feb 16, 2006 2:20 pm ]
Post subject: 
marc, what type of problems were you having before reconfiguring the front end as a slave backend? Would the video stop completely or would it play then pause then play agan?
Author:  duhasst [ Thu Feb 16, 2006 2:39 pm ]
Post subject: 
HD content over 100MBit works just fine. Sounds like an issue with your infrastructure. If your using a hub. Throw it into the garbage and buy a nice switch. Then make sure your ports are coming up correctly. I don't use Auto Negotiate. I set my NIC cards to 100 Full and I set the switch ports to 100 Full.

I've been running a backend with 2 Air2PC HDTV cards for about 4 months now. Its running on a AMD 1900 w/1GB RAM, lots of storage (R5A22). I initially tried testing wireless. 802.11g can't sustain 19MBit/sec throughput to my frontend (AMD64 3000, 1GB RAM (R5A22). So, I moved to wired. I have recently read a story about someone getting HDTV content streamed from a Microsoft Media Center to an XBox 360. Too bad its MS puke.. but same concept. They used 802.11A and setup a dedicated network just for the HD streaming. They could get it to stream HD content but you couldn't use the network for anything (not even web browsing). I haven't gotten around to trying this. I was going to pickup to cheap 802.11A cards and make a private network for my backend and frontend.

I hope that helps are gives others some ideas to try.

-duhasst
Author:  marc.aronson [ Thu Feb 16, 2006 7:40 pm ]
Post subject: 
Thanks for the replies. The problem I experience on the remote front end is a brief pause every 1-2 seconds of playback. The log shows the dredded "prebuffering pause" message. I’m running a P4-2.8ghz backend and a P4-2.4ghz front end – detailed config info below. They are both connected to the same Siemens switch (not a hub). Here is what I see:

1. NFS copy of a ~400mbyte file from the back-end to the front-end takes ~34 seconds => transfer rate of 91mbps, sustained. The “cp” process is running on the front-end. Based on this, I believe my network is ok.
2. Playing back 1080i content on the front-end machine through the myth interface results in frequent “prebuffering pause” messages in the .xsession-errors file.
3. Playing the exact same recording on the front-end machine through VLC or mplayer plays back perfectly.
4. 720p and 480i recordings will also play back properly in myth.

I then re-configured my front-end into a combination salve-back-end and front-end. The recording still sits on the master backend machine, but the master backend’s “/myth/tv” directory is NFS-mounted on the front-end box. The results are:

1. Smooth playback of 1080i on the front-end box using mythtv when nothing else is happening on the master backend.
2. Smooth playback of 1080i on the front-end box using mythtv even when the master backend is busy recording two shows -- one a hidef channel over firewire/DCT-6200 & the other a std-def channel via the PVR-250.
3. Prebuffering pause only happens when I am trying to playback a 1080i show that is still in the process of being recorded.

Based on this, I think my network is OK, but I would certainly appreciate any thoughts you may have on what else I should dig into, thanks!

Detailed config info:

Front end: P4-2.4ghz, 512mb ram, FX5200 video card, Nvidia driver version 6629

Back end: P4-2.8ghz, 512mb RAM, geforce3 video card, nv driver.

Marc
Author:  duhasst [ Fri Feb 17, 2006 2:18 pm ]
Post subject: 
did you try checking if the frontend is doing any deinterlacing? if so did you try any different deinterlaces or turn it off?

Another thing you can try if they are install. On the backend while you try playing something run an iostat or a vmstat and see what kind of stats your getting. If your not familiar with these tools just do a google and you should get good info.

Could be drive contention for whatever reason on 1080i files (odd compared to the 720p but you never know).

Also, did you increase the audio buffering at all? I would try upping the playback buffering on the frontend and see if that helps.

I do believe your network is solid from the tests you tried.

-duhasst
Author:  mschlott [ Fri Feb 17, 2006 2:24 pm ]
Post subject: 
Marc, I was seeing exactly the same symptoms when trying to watch non-hd myth recordings via a remote front end. Sometimes I could watch a show, and it would play fine, until I rewound changed channels. Then it would pause every one or two seconds.

I found I could watch the same recordings on my wireless laptop using Windows Media Player, by mapping a drive from the myth back end. I had no problems with pausing. At the time, I wrote it off to my laptop having a better wireless connection. I also did some file transfer tests via NFS while testing my wireless and found I could sustain very high transfer rates via NFS over wireless.

Once I get my display problems worked out, I'll break out my remote front end again, and configure it as a slave backend and test to see if my problems go away.
Author:  marc.aronson [ Sat Feb 18, 2006 11:27 pm ]
Post subject: 
While I don't have a solution, I do have some interesting data from "vmstat".

1. While playing back a 1080i recording, cpu is typically 18% idle and wa=0% (wa is "time waiting for I/O"). Things look this way if I am not doing any recording on the backend OR if the recording is going to a different file than the one I am playing.

2. While playing back a 1080i show this is still being recorded, CPU is 0% idle and wa is running 25% - 30%.

So it looks like a ton of CPU time is going into "wait for I/O" whenver I am playing back the 1080i show that is in the process of being recorded. Not sure yet how to use this to solve this problem, but it seems useful.

Duhasst -- I am not de-interlacing. I use 1080i as my display resolution so that the TV is doing the deinterlacing. In terms of audio buffering -- I selected the "extra audio buffering" option. I also tried increasing the size of the HD ring buffer without impact.

I'll do some more digging -- ideas are appreciated, thanks!

marc
Author:  mihanson [ Tue Sep 19, 2006 10:00 am ]
Post subject: 
I just wanted to give this thread a little nudge... Has anyone successfully been able to play/watch live HDTV from the master backend to a remote frontend over wireless (802.11g/Super G/802.11n)? What about using deticated network using a crossover cable and a wireless bridge? I'm thinking of getting a small HDTV for another room and setting up a remote FE in there. Running a wired crossover from the MBE to the remote FE is not practical. I'm not sure it would even be possible for me. Firestops inside the walls may prevent me from getting the cable down the wall. Besides, who wants to crawl around in the attic trying to run cable thru the walls if they don't have to? ;) Any more input is appreciated.
Author:  marc.aronson [ Tue Sep 19, 2006 8:56 pm ]
Post subject: 
My wait for I/O time went to virtually 0% when I increased my memory from 512MB to 1GB. I haven't gone back to test running over the network subsequent to making the memory change, but there's plenty of evidence out there that you can play HD on a remote front end using a wired network. For wireless you will need either super-G or "N", as actual throughput is typically 1/3rd of what it is rated at. ie: G only gives you 18-19 mbps. Even with super-G or N the challenge will be the consistancy of the signal. If you live in an area with close-by neighbors, all running wireless networks, you're odds of success are lower. If you live on a rural setting where the neighbor's house is 1/2 mile away, you've got a better chance. Also, using directional antenneas should also improve your odds.

Having said all of this, I suspect you will need to try it to know if it will work for you. Good luck!

Marc
Author:  duhasst [ Tue Sep 26, 2006 8:33 pm ]
Post subject: 
mihanson wrote:
I just wanted to give this thread a little nudge... Has anyone successfully been able to play/watch live HDTV from the master backend to a remote frontend over wireless (802.11g/Super G/802.11n)? What about using deticated network using a crossover cable and a wireless bridge? I'm thinking of getting a small HDTV for another room and setting up a remote FE in there. Running a wired crossover from the MBE to the remote FE is not practical. I'm not sure it would even be possible for me. Firestops inside the walls may prevent me from getting the cable down the wall. Besides, who wants to crawl around in the attic trying to run cable thru the walls if they don't have to? ;) Any more input is appreciated.


802.11g no dice. I've tried that. I have my 802.11a stuff show up this week. So, I should be able to give you an update next week if it works. I've only heard people getting 802.11a dedicated network working for HD streams. The 802.11n stuff I've read about conflicts with 802.11g networks at the moment and if its dedicated there is a distance issue (though they say it will go super far.. not the case right now). 802.11n is so draft right now, plus the cost is crazy that you might have to dump once the draft is final. I'll look at 802.11n next year. I found 802.11a gear cheap so I'm going to give it a try. I'll let you know.

--duhasst
Author:  Liv2Cod [ Wed Sep 27, 2006 1:02 am ]
Post subject: 
Interesting stuff going on over in the powerline ethernet camp ("Homeplug alliance"). May deliver the bandwidth needed for HD someday. (But not today...)
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