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THarper

Topfield recording bitrates

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Hi there:

I have posted this in another thread, but thought it might get more visibility out here in a thread of its own, and it is probably of interest to various other SD STB owners too (since the bitrate is a very big influence over the picture quality).

What I have done is collate the various bitrates for stations around the country based on Topfield TF5000PVRt recording file sizes per hour - this is from postings people have made in this forum and email submissions people have directly sent me.

It is online at http://www.impactinvesting.dyndns.org/PSNW...TVBitrates.html (and also at http://users.bigpond.net.au/tharper/DTVBitrates.html - but some people are having problems accessing that copy).

If anyone has additional "readings" from their Toppy (for the locations I have already listed or somewhere different), please PM or or email to me (email link is on that web page), and I'll update the table accordingly.

ted.h.

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The table on that webpage has now been updated with a few more "datapoints". Thanks to the various people who have emailed updates today; keep them coming as you find them.

Already the variance on some channels (eg SEVEN and NINE) between locations seems to go some way to explaining why in some locations people complain about MPEG artifacts and others - watching ostensibly the "same" program - don't see it, on close enough to identical equipment. Also, why some operational problems (with various STBs) might occur in some locations and not others.

I guess a good thing is that even the slowest bitrates we get anywhere (of the locations I have data for in the table) are well above the "norm" for Standard Definition DTV in Europe. Some countries there apparently have a "standard" bitrate of 2Mbit/sec, and their high-quality channels only 3-4Mbit/sec - any wonder that SD DTV has a bad reputation there for artifacting which we just don't see here with our typical 6-10Mbit/sec rates.

ted.h.

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I guess a good thing is that even the slowest bitrates we get anywhere (of the locations I have data for in the table) are well above the "norm" for Standard Definition DTV in Europe. Some countries there apparently have a "standard" bitrate of 2Mbit/sec, and their high-quality channels only 3-4Mbit/sec - any wonder that SD DTV has a bad reputation there for artifacting which we just don't see here with our typical 6-10Mbit/sec rates.

ted.h.

How do people with DVD recorders cope with such a high data rate when trying to record a movie onto a single disk? Or do these recorders re-encode the data stream to a lower rate?

Byron

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I wouldn't have thought it would have been a problem for the current, even older recorders. It takes me about 15-20 mins to record a 4.7gb dvd-r in my pc's pioneer a05. So thats about 5MByte/s or so. Thats about 40Mbit/s.

I'm not sure what the speeds dvd+rw in some of the dvd recorder stb's are but if its anything like the pc burners they should have the speed to be able to do around 3-4 streams at once if the rest of the hardware is capable enough.

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How do people with DVD recorders cope with such a high data rate when trying to record a movie onto a single disk? Or do these recorders re-encode the data stream to a lower rate?

I'm not sure what sort of DVD Recorders you're talking about, so I'll give you two different answers (for the same low, low price (grin)):

1. The stand-alone DVD recorders - that you might feed via SVideo output from a "normal" set top box - do their own encoding on the _analog_ output from the STB, and hence the user can control the space/quality trade-off.

2. When you make a DVD copy of the digital recording from a PVR (say with a Topfield TF5000PVRt copied to a PC via USB2 cable), the resulting file _is_ that size (since the video is MPEG2 in both cases, and just basically copied directly, rather than re-encoded). I did a test DVD-R from an ABC stream via this means and it was over 7Mbit/sec, so the 4.7Gbytes on a DVD-R gets used up pretty quickly. NB: You could re-encode the stream on the PC to a lower bitrate/quality via any of those "DVD shrinking" tools.

BTW, the high bitrates we have here are what cause the "recording times" quoted on the promotional literature for various PVR boxes to be out-of-whack with what people in Australia actually get in real-world use. Most of the literature I've seen quotes "80Gb hard disc gives XX hours of recording (based on a 4Mbit/sec stream)". When the actual SD streams in Australia are between 6-10Mbit/sec, it's pretty clear that the hard disc space gets eaten up proportionately rather more quickly than customers might at first expect.

NB: This is not to say that there's anything bad about having high bitrates on SD streams, far from it in fact!

ted.h.

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There is a lot more data in the stream than what we see as recorded on our box...for example, the gig per hour that is sent by ch 7 here on the Sunshine Coast is 8.5 gigs per hour, but the recorded file for the same hour on the Toppy is 4.6gig ....there is a lot discarded for some reason or other...I don't know the tech side of it...only what the gig usages are for total stream size as is sent from Ch 7 and also the size as it appears on our box.

foss

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2. When you make a DVD copy of the digital recording from a PVR (say with a Topfield TF5000PVRt copied to a PC via USB2 cable), the resulting file _is_ that size (since the video is MPEG2 in both cases, and just basically copied directly, rather than re-encoded). I did a test DVD-R from an ABC stream via this means and it was over 7Mbit/sec, so the 4.7Gbytes on a DVD-R gets used up pretty quickly. NB: You could re-encode the stream on the PC to a lower bitrate/quality via any of those "DVD shrinking" tools.

Thanks Ted,

makes me glad I have a PVR and not a DVD-Recorder.

B

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