HD data rate

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John Disdle
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Joined: Dec 28 2000

A recent search indicates that DV has a data rate of 25Mbps.

The Canon HV20 in HDV mode has a resolution 1440x1080. A SD DVD from Vegas HD Studio, and DVD Architect is much better than from edited DV footage.

The Canon HF M36 has several HD options.
MXP = 24Mbps 1920x1080
FXP = 17Mbps 1920x1080
XP+ = 12Mbps 1440x1080
SP = 7Mbps 1440x1080
LP = 5Mbps 1440x1080

XP+ plays back in Vegas reasonably well, FXP is a little more jerky, and may be worse with a large project.

There is 8Gig internal memory, and a slot for a SDHC card. Using the relay record function, recordings continue on the external memory when the internal is full.
Page 36 of the manual is confusing.
The notes state the relay record is deactivated when you – turn off the camcorder. Change the mode switch or the operating mode, and selecting the memory card for recording movies.
This is not looking too good. I have a card on order, but it would be re-assuring if this was a mistake.

The bottom line I think, is which HD mode is going to give as good or better than the HV20 HDV 1440x1080.

MAGLINK
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Joined: Mar 8 2007

I find that AVCHD MXP at 1920x1080i 50i 24mbs is far superior to HDV.

It looks a lot nicer but the codec can be problematic to play back and edit so I transcode it to pro res LT for editing.

John Disdle
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Joined: Dec 28 2000

Thanks. I think Pro res is Apple Mac? I have a lowly Intel 3Gig 2 core duo + 2Gig ram. It's going to struggle with anything like that I think!

It's going to be either FXP or XP+ for editing, so I just wonder how much of an improvement I will get?

The 16Gig card arrived and the relay record function needs to be reset after switching off, or changing anything. It would have given me about three hours at FXP. Instead, I can select to record photos to the 8Gig internal – that`s a lot of photos, and about two hours of movies to record to the external SDHC card. This is not an ideal situation, and had I known, would have preferred something with just a card slot.

MAGLINK
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Joined: Mar 8 2007

AVCHD is a complicated codec to edit direct so that is why I use pro res LT on my mac's, it is OK on an intel 2.16 dual core with 2gb ram.

There are lots of posts regarding editing AVCHD on the PC so do a search and you will see what best to do, it may be that you can view and edit at reduced bandwidth and then get it to render up to the full 1920x1080 24mbs, 17mbs should be fine too for most things but the basic AVCHD codec looks a lot nicer and cleaner than HDV.

Steamage
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Joined: Nov 11 2003

AFAIK, the 17M AVCHD setting is roughly equivalent to HDV (MPEG2 @ 25mbps).

All but the latest and fastest computers and NLE programs (PC or Mac) will struggle a little with AVCHD editing without a bit of help. That's a function of the codec more than the data rate. The options are:
- add a deditcated hardware card to cope with the codec (I think Canopus have something of the sort)
- transcode to a less-compressed codec, such as Pro Res, at the cost of more time during capture, more disc space and perhaps more time when rendering to your final output;
- buy a bigger, faster computer and upgrade your NLE so that you can edit AVCHD natively.

I'm ducking the issue for the time being, sticking with HDV and Avid Liquid. MPEG2 @ 25Mbps from tape to timeline to Blu-ray without the need to re-render anything except transitions etc, with an instant archive on tape. I don't mind the real-time capture process, because I need to review all the content anyway before I start editing.

Mark @ Steam Age Pictures - Steam trains on video in aid of railway preservation societies. Latest release: "Mainline 2012, LMS Locomotives", on DVD or Bluray Disc.

steve
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Joined: Apr 8 1999

John,

Cineform Neoscene will give you the benefits of an intermediate CODEC without the disadvantage of moving to an Apple system. Details of the product are here:

http://www.cineform.com/neoscene/index.php

and a 7 day trial from here:

http://estore.cineform.com/downloads.aspx

You will of course need a considerable amount of HDD space with any of the intermediate CODECs.

Steve

Alan Roberts
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Joined: May 3 1999

John your original comparison table is comparing apples and pears. DV is 25Mb/s but uses DCT coding, intra-frame. This means that each frame stands fully alone on the tape, and is assigned 1Mb for coding. The compression is only about 5:1, but that's really about as far as you can go and get decent results with intra-frame DCT.

HDV is MPEG2. So half a second of video is coded as a single entity, frames do not stand alone. Only one frame in each group is fully coded intra-frame, just as in DV, the other frames are coded only as differences from the two frames at each end (one in 'this' group, the other in the 'next' or 'previous' group. It's not even that simple, because the coder assumes intelligence in the decoder, and codes the difference between the actual input frames and the frames that the notional decoder would produce were there no transmitted data for them, these differences are compressed and sent as correction signals.

By the time you get up to AVC, you're using MPEG4, which follows roughly the same principles as MPEG2, but has a lot more clever tricks to play. For example, the coding blocks can change size depending on motion and complexity. Also, in some implementations, individual blocks in the predicted frames can be coded as I frames if there's too much change. and so on.

So, the data rates make sense for comparison only if your comparing similar systems. I have a simple rule-of-thumb though, that MPEG4 can use between 70% and 50% of the data rate of MPEG2 for similar results, and that PEG2 can use between 70% and 50% of the data rate of intra-frame DCT for similar results. These factors are changing continually though, because clever people are continually fine-tweaking the coders, so new products can often deliver better pictures at the same data rates as older ones, at the same data rate.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

John Disdle
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Joined: Dec 28 2000

Thanks Gary. I havn`t done much with AVCHD yet, and really want to keep it simple. I will search and see what turns up.

Thanks Steamage, that gives me an idea of what to expect. I thought I had seen the last of hardware cards, a pc upgrade would be the answer.

Thanks Steve. Keeping it as Mpg until conversion to DVD, saves disk space and time. So I would like to continue with that.

Thanks for that explanation Alan. I think for now, it`s a case of seeing what Vegas and my pc can cope with. From what I have seen, the results are an improvement over DV, so I must be winning.