Live and Recorded TV Bitrates - Why the difference!

[red_shed2000]

Hi All,

I use the nVidia Purevideo decoder for live and recorded TV as I have read that it performs the best with an nVidia card (Geforce 6200).
I thought I was imagining things but I could have sworn that recorded TV looked better on my system than live TV. I couldn't think of any reason for this so just thought that it was my imagination.
HOWEVER, I was playing around with settings today and noticed that the Purevideo decoder has a bitrate level that shows whats being decoded at any particular instant. During normal TV it flickers between 2 - 2.5 Mbps (which struck me as low) so I watched it while playing recorded TV and it shot up to approx 4 - 4.5 Mbps - APPROX DOUBLE!!

So why is this? Is there anyway you can increase the quality of Live TV or indeed the recorded quality (although it is already higher)? Has anyone else noticed this?
Any help would be good!!

[nigelbb]

What TV tuner card are you using? Analogue or DVB-T (Freeview)?

[red_shed2000]

Sorry forgot to mention that - am using 2 x Twinham DVB-T

This is really odd - I deff get a better recorded picture and would love the same quality on live TV!

I've read about this issue before but, as I only watch recorded TV, I've never bothered to look into it further.

As far a I can remember it involves editing the registery settings.

It may be worth taking a look at TGB and the XPMCE forums

[red_shed2000]

ohhhh - editing registry doesn't sound good! I'll have a look at the other forums so thanks for the tip!

This does seem very odd - has anybody else noticed this or done anything about it? Is there anywhere you can adjust the quality of recorded TV (or live TV) in MCE - I had a good look last night but couldn't find anything.

[nigelbb]

You have DVB-T (Freeview) tuners so the exact same MPEG2 file is recorded to disk as is received over the air. In fact even with analogue there is no Live TV as such but rather the MPEG2 is recorded to disk & then replayed a second or two later.

The differences in picture quality you are seeing is because some channels are transmitting at a higher bit-rate & what you recorded was one of those.

[red_shed2000]

Originally Posted by nigelbb

The differences in picture quality you are seeing is because some channels are transmitting at a higher bit-rate & what you recorded was one of those.

Thanks for your response Nigel, however, I did an experiment last night where I watched a channel and recorded it at the same time. While watching I also monitored the bitrate and the same happened again - 2 - 2.5 Mbps while watching live TV then when I watched the EXACT same thing back it looked to be better quality and was registering 4 - 4.5 Mbps!

Anybody any ideas!!!!!!

[HiZ]

Couple of reasons maybe but Im gonna look at this when I get home.

1. The Microsoft recorded format DVR-MS or whatever its called isn't the same as what comes over the air. They fiddle with it, just as you do when burning to a DVD. It will only be the formating and possible removal of unused PID's such as subtitles and second audio channels. It bhardly means the video bitrate should increase though.

2. Once the compression has been applied at the broadcasters mux there is absolutly no way of getting it back. WIGIG. You can artificially make the bitrate higher but they quality will still be back where you started. It seems like your card isn't decoding it to its best ability on live streams but i kind of doubt that.

Very odd and very interesting. Now where's that transport stream analyser gone....

[HiZ]

Originally Posted by red_shed2000

Thanks for your response Nigel, however, I did an experiment last night where I watched a channel and recorded it at the same time. While watching I also monitored the bitrate and the same happened again - 2 - 2.5 Mbps while watching live TV then when I watched the EXACT same thing back it looked to be better quality and was registering 4 - 4.5 Mbps!

Anybody any ideas!!!!!!

Which service are you monitoring by the way...i'll try to find out the exact bitrate of it.

Also consider most muxes are statisticaly multiplexed so their bitrate can vary a lot depending on the material at the time. If you watched and recorded at the same time then it rules that out.

[red_shed2000]

Most of the live channels that I have monitored give roughly the same bitrates (between 2 and 3 Mbps). Recorded TV always gives 4 - 5 Mbps.
Do these figures sound low to people anyway?

Anybody else with the Purevideo decoder give this a go and see what results you get?

[nigelbb]

The Purevideo decoder must be reporting the bit rate of Recorded TV incorrectly. DVB-T is generally broadcast at about 2-3Mbps. The way to confirm is to look at the size of a recorded TV programme & then calculate the bit rate from that. Alternatively use another tool to examine the Recorded TV file.

[red_shed2000]

That's a very good idea!! I'll do that tonight.

Thanks