New JVCPRO HDV codec
My understanding is that JVC uses a new codec to accomadate the new 60P frame rate on the HD200 / HD250.
Does this new codec improve on the existing 6 GOP (19mb/s) codec? If so, this would mean that 24P/30P footage COULD have less compression artifacts. |
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Thanks,
I know this. I'm asking since they did update the codec to offer 12 GOP for 60P, was there any change AT ALL to the existing codec for 24P/30P? |
In my opinion ther 12-GOP if anything could potentially worsen it.
Or does it only do 12-GOP on the 60P only? You really can't get much better than 6-GOP for mpeg2 that actually works well, save for straight I-Frames, but that probably wouldn't work at all. I have not noticed any kind artifacting at all with my HD100 except for the CA when I zoom in past 75%. |
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It is VERY possible to use 2:1 pulldown to get 25p and 30p carried by 50p and 60p, but has JVC said that's what they'll do? The codec issue is covered at: "How much better is 12 GOP?" |
I though it was not pull down but instead placeholders. When the 24p is captured in Liquid the stream is read as 59.94 but when the clip is in the rack it is 23.98. The placeholders are disregarded when the clip is actually placed in the rack (bin for all other NLE's). When Liquid writes the 24p back to tape it will embed it in 59.94 just the same way it was captured from the tape (markers back into position). So upon capture it always treats the stream as 60p and then disregards placeholders.
Conversely when Liquid captures 30p the stream is aways read as 29.97. |
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I wouldn't be at all surprised if it does straight 60P recording only then adds whatever flagging to the bitstream to get your 30p/24p formats.
I believe thats what the varicam does. Does the HD100 derive 24fps from 30fps? Or does it derive 24p/30p from the 60P signal it generates internally (like you get live on the component outputs) |
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So 30p is a direct encoding of 30fps, because the format allows for it. 60p was part of the HDV spec from day one, they just didn't have an encoder that could handle that much data until now. 24p wasn't part of the spec so they implemented it within a 60p transport stream. Quote:
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Because there are 60 frames being processed by the DSP, that's how they can do their "motion smoothing" filter -- they overlay a ghosted version of the "dropped" frame, so you get the motion from two frames blended into one. Same thing but slightly different with 24p, they run the CCD at 48hz and scan 48 frames per second, then drop half of them and record the other half. It's a little different because the camera head output is still 60fps, so there's a duplicate frame added every once in a while to round out the 48fps sequence to 60fps. That's only on the analog outputs though; internally it only works with and stores 24 fps. |
Wow! Thanks for your very thorough clarifications Barry! :D
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Not clear -- if there would be any difference between the current 6 GOP option and a 12 GOP with 2:1 pulldown. Need coffee. |
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