FH Mode GOP rates for 50/60fps

rambooc1

rambooc1

Well-known member
Has anyone experimented with different GOP's for 50/60fps? I see that Ipowell has reduced GOP to 3 for his 50mbps reliable patch at 720p 30/25fps, but i'm more interested in improving high action with 50/60fps in 720p.

Chris (cbrandin) have you played around with these, ipowell has already said he hasn't in his thread. This would be with a Sandisc Class10 Extreme 30Mbps card.

Cheers Rambo
 
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I expected not many (if anyone) had played around with this, most people here are interested in 24p at 1080 res, so looks like i will have to start from scratch and report my findings. What i do here may make FHD mode (1080) unusable or unreliable as i really want to push 720p 50/60fps to max and get the GOP length down, 30 or 25 "P" frames seems way too high for fast action.
 
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I haven't played with it much. One thing that comes to mind is that for slow motion a GOP of 12 seems good because it will match the 12 GOP of 24 fps clips (even if they are wrapped in a 60i wrapper because a wrapped GOP of 15 is the same as a progressive 12 GOP). For PAL, one would use a gop of 13. This assumes that default GOP's are used for 1080 footage.

Chris
 
Chris not to go off topic, but has it been proven that gop of 12 is the best value to keep with the hack (for fhd 24pn checked), some people have 10, 6 or 4 ,some went up to 15, im sorry if the question has been answered before ..
 
Sorry guys i stuffed up the Title it's meant to be SH mode not FH.

Please keep this thread to SH discussions, this is about 720p at 50/60fps not 1080i

Sorry Chris, might have misled you there. I'm only shooting in FH mode and exporting final at 720p 50fps, so it does not have to match other footage. I'm thinking of starting with a GOP of 6 which is double what ipowell is recommending for 720p at 25/30fps.

Rambo
 
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lpowells setting is proportionally correct. 3gop is stable at 30fps, just as 6gop seems to be stable at 60fps. Ive tried 5,3,2,1 gop for SH and it crashes at variable complexities, but 6 seems to have stood up to static grass. Lowering gop increases filesize and increases the risk of dropframes though, so you'd have to consider if having missing or stuck frames is worth whatever quality improvement that might bring.
 
This PAL (50fps) i'm specifically aiming for, so it's probably worth trying 5, 6 and 7 GOP.

What i'm trying to achieve here is obviously a higher data rate for 720p @50fps, to ensure a more accurate fast action capture, the shutter will also be 1/250, so this will add additional complexity.

This footage will be combined with 720p 50fps from a Pana HMC152, which records at 24Mbps AVCHD but with B frames.

All footage from both cams will be transcoded to Cineform Neoscene for editing.
 
The rule of thumb is that the GOP length should be the number frames in 1/2 second. This is fairly universal. Now, for action shots there is a lot to say for shorter GOP's. But all this is a matter of convention. I take Lpowell's findings very seriously - he does the homework to back them up.

Chris
 
cbrandin said:
I take Lpowell's findings very seriously - he does the homework to back them up.

Chris
Click to expand...

So do i, i've been using them exclusively and had no errors for 2 months of any kind using them. But i now have a need for 50fps.

Thanks Chris, you know i appreciate your work and that of the others that have done testing on their cameras.

R
 
Thanks to you both for your votes of confidence. I'm planning on doing further testing on PAL modes, as I was only recently able to provide support for them in my Fast Action patch as a follow-up to my initial NTSC-based research. When I find time, I'd also like to see if the newest patches can be applied productively to my original High Reliability patch.
 
First round of testing and this looks good. Much more detail and cleaner images when camera is in motion. Side benefit is with a GOP of 6, editing is quicker in Sony Vegas with the non- transcoded 720p 50fps files. Maybe my imagination, but jello looks to be improved too.

How good is the 20mm pancake, awesome little lens. How do they get f1.7 out of such a small opening?

R
 
been playing with this a bit myself....
have GOP at 5 for 720_60p and seems fine (based on lpowell fast-action, but no 30p). bitrates are low though: < 20mbps. think i need to undo lpowell's adjustments to get the bitrate back up.

additionally, i've got GOP at 6 for 1080_24pN and that is looking really nice with bitrates around 45mbps.
 
I know I will be branded as Heretic but
I have used alot of settings on GH1 but 720 p60 gop 5 is my favorite of all settings for GH1 ,
I can review in camera , get no errors looking at data and more importantly for me when I check raw footage off my editor on 12 ft screen it looks solid ,The 1080 stuff I have yet to like(maybe lack of b frames).and on the 12ft screen does not look as ggod As a comparison 5d 7d footage was too fuzzy 1080p on GH13 too sharp like some auto sharpening was happening but 720p on gh13 just right except for FPN regardless of setting .But only really noticable in low light I think this sensors sweet spot is 720p and so thats what I use so far . I can do slo mo easy or simply convert from there to 24p . It also scales and cuts nicely with 1080p 24. but truthfully not needed for me

Dont know about 720p 50 as I am in NTSC land

looking forward to lower noise in GH2 ,and HDMI out for at least monitoring even better if it was like HV20

Larry


Larry
 
Mjpeg was also promising it also looked good on small screen solid as well , but was noisier than avchd regardless of setting and conversion was messy so was abandoned.
 
hey larry,
why did you feel the need to convert mjpeg at all? i'm pretty sure any NLE can handle it...it's intraframe and fast in general.

i'd love to be able to use mjpeg, but the 14khz audio and 3m50s recording limit are deal breakers. for me, it seems to hold more detail in static shots (forced higher bitrate), but then loses out to the avchd for detail in shots with lots of movement.

i've tried using avchd 720_60p with GOP 5 in a 24p timeline, w/o slowmo, but every 4th frame has a slight duplicate/ghost. have you noticed this at all?
 
All prelm test we just dragged and dropped as it was to see if we could even use it as its colour and contrast are quite snappy ...
But no matter what we did noise was alot higher than the Avchd . If your project was web based however I dont see a big problem with it.

what settings are you using for AVCHD

we have no flashing , no artfacts ,,just smooth....Funny though I thought I would try I powels setting on on of the cameras and "boing" it just locked up ...
No offense Ipowel you are doing a great job!.....probably something I did

Larry
 
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