HV20 not really 24p??? Is this guy right?

[Barry_Green]

Rick, you may have a point -- the interlaced 4:2:0 could perhaps be complicating issues. I hadn't factored that in when I wrote the original response. You might need to use software that intelligently understands how to reverse out the pulldown and at the same time compensate for the 4:2:0 color recording; if the software simply drops fields then yes it isn't going to work 100% right. But if it understands how the chroma is split across fields, it should be completely reversible.

But -- this is a $1,000 camcorder too. It's not really designed to have pulldown removed. Canon didn't even put the flags into the data stream to support pulldown removal, and when users complained enough, Canon said (basically) "sorry, that's not what this product is made for." (their response was posted on DVInfo somewhere).

I'd actually wonder about the V1U as well; it uses the same interlaced 4:2:0 recording system, it should potentially have the same issue on every 4th frame, if interlaced chroma is not accounted for.

As far as the mantra about "not recording 24p", buckle your seatbelt for a surprise -- practically no other camera records "24p" either. Not a $100,000 HDCAM F900 (it records 24PsF with segmented fields instead of frames). Not a $45,000 VariCam (it records 24p embedded within a 60p data stream). Not a DVX or XL2 or DSR450; they all record 24p-within-60i (same as HV20) or 24pA-within-60i (which still uses a form of pulldown but totally bypasses any interlaced-chroma issues). Not a Sony V1U, it records 2:3 pulldown just like the HV20. Not a JVC HD100/HD200/HD250; they record 24p-within-60p using 2:3 frame-repeat flags. The *only* cameras out there that can RECORD a straight 24P are the HVX200/HPX500 using 720/24pN mode. In 1080 mode they still use the same 2:3 or 2:3:3:2 pulldown systems.

Curiously, Canon does offer a straight 24p recording mode on their 24F cameras, but their footage is sourced from interlaced chips so while it's a progressive recording format, the source frames aren't sourced from progressive chips, so I'm sure there are plenty of purists who would complain about that too.

So what you want doesn't exist. And it most certainly doesn't exist in a $1000 palmcorder. Trying to start a campaign to accuse Canon of deception is either naive, misinformed, or ill-guided. They are employing the exact same recording mechanism everybody else does. Your problem (insomuch as a problem exists) may have more to do with the HDV format's 4:2:0 color sampling than it does with anything else. But lots of people seem to be happily extracting pulldown on the Windows platform with no residual interlacing artifacts, so I'd expect you've just got some sort of error in your process somewhere.

 

[Barry_Green]

... and David posted while I was writing that, so it may turn out that there's no issue with the HV20 and removing pulldown at all.

 

[manbart]

People have found work arounds for this 24P problem with the HV 20 using freeware. It's somewhat complicated and labor intensive, or you can spend $250 on Cineform's Neo HDV which will deal with this and works with Vegas 7

 

[sean90291]

For best results, one would extract the pulldown out and restore the footage to its original 24p state. The HV20 doesn't make this easy, because it doesn't include flags in the data stream. But that doesn't mean it's impossible, it means you have to take another step and run a pulldown-extraction program.

To your knowledge, Does Cineform's NeoHDV do what's needed as far as pulldown-extraction? I mean, I know it does pulldown, but given that the HV20 doesn't contain flags, does Cineform's software automatically detect the HV20's cadence and duplicated frames (because as was pointed out, the HV20's cadence changes from scene to scene).

 

[vsansal]

To your knowledge, Does Cineform's NeoHDV do what's needed as far as pulldown-extraction? I mean, I know it does pulldown, but given that the HV20 doesn't contain flags, does Cineform's software automatically detect the HV20's cadence and duplicated frames (because as was pointed out, the HV20's cadence changes from scene to scene).

Yes, it does. All you need to do is select inverse pulldown. It is that easy and it does all of this during capture.

 

[sean90291]

Is there any loss in resolution after Cineform's pulldown? I know deinterlacing causes a loss of resolution (in fact you're not supposed to deinterlace AND do pulldown-extraction with Cineform--you're just supposed to do the pulldown witout deinterlacing apparently).

 

[Cranky]

The reason the lack of completely reversibility is the 4:2:0 60i encoding which has only chroma value for pixels over two scan lines -- these scan lines may contain data from different frames, cause chroma cross-talk. The luminance is perfectly correct. Luma is encoded at 60i, and chroma at 30p, you can extract 24p from luma but not fully from chroma. If the pulldown is extracted correctly, the chroma cross-talk will only appear on every fourth frame.

Whoa, I have never thought about it. Anyway, what looks awful for you as a professional, will (and does) look just amazing for a regular consumer. Even crippled as it is, HDV-2 provides so much more detail compared to DV that consumers are in awe. Heck, talk with professionals about 12-, 10- or even 6Mbps 1080i feed over cable or about HD-Lite and all you'll hear is cursing. But regular consumers think that this castrated HDTV is the best thing they ever saw. They love it. The HV20 is a consumer camcorder after all. To those who disregard Rick's accusations of HV20 as a non-true 24p camcorder, please check out this article: http://www.dvdfile.com/news/special_report/production_a_z/3_2_pulldown.htm It explains how A,B,C,D film frames are pulled down into A1A2, A1B2, B1C2, C1C2, D1D2 field sequence.

Judging by this sequence it seems clear that every fourth 24p frame (B) in is split between two 60i frames and its croma is "borrowed" from the frame A. I believe that one frame out of four having croma crosstalk is not noticeable to most consumers, so while HV20's 24p is not truly reversible, it can be considered "true" 24p for a consumer appliance. This is just another small lie in a series of lies, like that HV20 is a true 1920x1080 HD camcorder, while in reality it is a standard 1440x1080 HDV-compliant device, with only 1920x1080 imager. Heck, the whole idea of having true 1080i HD at 25Mbps is laughable, because the compression kills the fine details and macroblocking is inevitable on fast-moving scenes. But HDV produces visually better footage than DV and this is all that matters for consumer market. No one cares about formalities.

What *is* an issue, and the reason I say "almost", is that Canon didn't put in frame/field flags to allow for easy extraction in post. That's a disappointment; it means that if you want to strip out the pulldown and access the pure raw 24p data you have to go shot-by-shot (because the cadence can change for every shot) and strip out the pulldown

By looking at the picture above I am curious, does HV20 writes video in chunks of five 60i frames?

I understand the remark about flagging, but considering that even budget DVD players finally became fluent in candence recognition (OPPO with Mediatek comes to mind first, and of course Faroudja and Silicon Optix chips), I suppose that this should not be a big deal for computer software.


---

Michael, Canon Elura User Pages

 

[Barry_Green]

By looking at the picture above I am curious, does HV20 writes video in chunks of five 60i frames?

Once recording starts, it's done in continuous sequences of 10 fields, with the pattern repeating after 10 fields. But every time someone stops and then starts recording again, the pattern is potentially interrupted. Which means the cadence is "off", and that complicates the whole system.

Some software can "guess" the pulldown sequence (like After Effects). Most NLEs don't. 24P video cameras are designed to put flags in the timecode stream, and NLEs are designed to recognize those flags. Canon didn't design the HV20 for pulldown removal, so they didn't put the flags in. If you're using software that can appropriately guess the pulldown removal, and you break your footage into individual shots, then there should be some automation possible to strip out pulldown.

A custom utility could strip out pulldown and compensate for the missing chroma information; I haven't heard of anyone producing such a product though, unless CineForm's products do it?

 

[SomewhereinLA]

I don't know much about the HV20, but I wonder if the sequence starts the same way each time you start recording? If so then to cine-compress the clip should be easy no guesswork needed.