Issues watching BBC (PSB1?) on LiveTV for XBMC

[NigelG]

Hi,

First off, thanks for some great software, I will be donating soon...

My issue relates to 'streaming' and playback of LiveTV from a Win7 install of nPVR to a standard RaspberryPi. This appears to be limited to the Muxes that use higher data rates for programming. I say this based on my limited understanding rather than actual knowledge. It appears to me that the BBC in particular tends to transmit a higher data rate (less compression?) I have seen this as larger .ts files when recording (nearly twice the size of other channels like 'Drama').

I have searched in vain for information that confirms this and was looking for any technical details that were available to confirm this.

The upshot of this is that while I can watch both 'Live' and Recorded' TV for many channels it is not really usable for BBC channels and is affecting the WAF (wife approval factor) which needs to be high so I can switch to XBMC / nPVR full time...

I will be 'overclocking my RaspberryPi this week (from 700Mhz to 900MHz) and hope this 30% increase in processing will be enough to overcome the shortfall I am seeing.

Of course this could be caused by limitations on the LAN. I am using WiFi (which is not ideal I know) but as the house hasn't been cabled with CAT5 is a show stopper for me. I was looking at providing a separate WiFi SSID just for the media players (separate uncontested channel). Is there any way of identifying the bottleneck, ie differentiate between processor power and connectivity.

Thanks in advance

Nigel

[mvallevand]

Bottlenecks in order as I see it

- 802.11n wifi is not reliable for HD. Unless you have no neighbours I am not sure how much bandwidth a different channel will buy.

- RPi is not always a good choice for an xbmc client and certainly not the best choice

- xbmc is not as mature a PVR client as NextPVR and it will drop put especially when changing channels.

- Live TV itself often requires faster processing than recordings because of reduced buffering.

Martin

[NigelG]

Martin,

Thanks for your response.

I'm not actually trying to watch HD, only SD. My WiFi is not 802.11n, I am using the older 802.11g. I am lucky in that I do not have any neighbours and therefore can control all the channels accross the whole of the 2.4GHz band. I was actually thinking of moving the Media connections to 802.11a (5GHz) so as to completely separate the traffic along with separate VLANs on my central switch to remove as much contention with other non-media apps as possible. But I take on board your comments and realise that WiFi is not the ideal medium...

I realise that RPi is not the best but I am willing to invest some time in it if I can get the functionality at this price point. I'm tantalisingly close, its just the BBC channels that seem to suffer from time to time.

I must admit I don't tend to watch much live TV and do even less channel surfing, I mainly watch time shifted programmes. The poor performance when changing channels while not ideal is not high up on the wish list, I would forgo this for a centralised PVR that I can watch common content across several locations. If I can do this using WiFi the flexibility would outweigh many other short comings. When I look at the cost of alternative distribution systems using CAT5/6 and HDMI switching my eyes water...

As you mention the heavy work is in the playback rather than recording of transport streams. I am hoping a 30% increase in processing powerin the RPi may overcome what I am experiencing.

Thanks again

Nigel

[mvallevand]

With 802.11g and an RPi, I guess you really should have less expectations, even if that might not be easy to convince SWMBO. It can be improved if you want to spend the money. If you can turn off de-interlacing does that help at all?

Also, if you'd like to place a 20MB sample somewhere I'd be happy to give it a try on various devices including my RPi to see if there is something that shows up in the file itself.

Martin

[gEd]

can you copy a sample recording onto the Pi's local SD card to test local playback ? (I have no idea).

[Graham]

can you copy a sample recording onto the Pi's local SD card to test local playback ? (I have no idea).

Can you test using a temporary CAT5 cable draped about the room for a day or several?

[mvallevand]

Can you test using a temporary CAT5 cable draped about the room for a day or several?

The RPi uses the usb bus for ethernet so testing with USB should be sufficient. It will be a good test of overclocking improvements on bandwidth for heavy hd but for sd overclocking shouldn't help streaming.

Martin

[NigelG]

Martin,

I have just 'overclocked' the Pi.

arm_freq=900
core_freq=333
sdram_freq=450
over_voltage=2

I have now played one of the files that was giving me trouble, 'New Tricks' recorded last week on BBC1, I had noticed that the programme was almost twice other similar recordings in that it took 1.8GB of storage compared with approximately 1GB for episodes recorded on other muxes (Drama?).

Before I overclocked the RPi I checked out the CPU Usage % in 'Summary Information'. The readings where high 90%s and hitting 100% every second or so. After the overclocking the CPU Usage % is typically mid 90%s with only a rare 100% being reported. I'm surprised it runs so hard all the time but maybe their are other processes making use of spare capacity?

Memory used is unchanged at mid 20%s.

I will try to play the same file again this evening in case there are other activities on the LAN that are causing the issue...

Fingers crossed, things seem much better since the RPi has been suped up... 900Mhz is described as 'medium' overclocking so it may be possible to squeeze a little more if necessary...

BR

Nigel

[mvallevand]

I feel 1.8GB for an hour long show is still pretty low bandwidth. The only thing I can imagine for taking that much cpu is the deinterlacing.

Martin

[NigelG]

Hi Martin,

My wife watched the recent problematic BBC1 (SD) version of 'New Tricks' last night with no problem so it looks as if the over-clocking has added just enough oomph to get the RPi to play the file with no issues... I again played 10 minutes of it with no issue this morning...

However, I recorded 'Requiem for Detroit' on 'BBC Four' (still PSB1) last night and it plays with the same stuttering that I previously had with the recording of 'New Tricks'. Checking the RPi CPU usage while watching the programme is constantly hitting 100%. Checking the file size it is more than 3GB for a 1hour:20min programme

I notice that you have mentioned 'de-interlacing' a couple of times but can't see any option that appears to relate to what your talking about.

I'm using a 720p TV. XBMC Sumary information shows 1280x720@50Hz. It was 60Hz but I changed it with no noticeable effect thinking that the RPi may have to transcode from 50Hz (UK standard?) to 60Hz (US standard?).

Thanks for sticking with this.

Nigel