75Mbps GH1 Peak Reliability Patch - V2 update

balazer said:
This patch delivers poor video quality in 720/60p. The GOP is too long. The codec in the GH1 accumulates visual errors over the length of the GOP. The GOP should be less than 14 frames long to avoid noticeably degraded video quality.
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That hasn't been my experience after shooting 300+ clips of high motion water footage in both 50 and 60 fps. The 50 has 100% success rate, the 60fps gave one card write error. Transcoded perfectly to Canopus HQX Lossless and edited in Sony Vegas Pro to final delivery.
 
Then your experience differs from mine. I did extensive testing of different GOP lengths, and also tested with this patch. I have updated my previous post with sample videos.
 
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Both those clips are recorded at less than 20Mbps. (average 17Mbps)

Why would you want record 720p 60fps in poor light.
 
It was just a quick test to illustrate how this patch performs poorly. The problem is just as bad under better lighting.
 
Peak bit rates aren't the issue. The issue is that the video looks poor with a long GOP, and the problem is corrected by using a shorter GOP.
 
This patch isn't optimized for 720p, period. That pulsing is visible and objectionable even when the camera is moving. A static shot was simply the fastest test I could think of to make the problem readily apparent.
 
balazer said:
This patch delivers poor video quality in 720/60p. The GOP is too long. The codec in the GH1 accumulates visual errors over the length of the GOP. The GOP should be less than 14 frames long to avoid noticeably degraded video quality.

Here are short clips illustrating the difference. The two clips were shot with identical camera settings: ISO 800, 1/60, sharpness=0.

lpowell_p75v2_0.MTS
my_27M_GOP10_0.MTS

Look for the pulsing in the detail on the wall. That pulsing looks really bad when I shoot skin and hair.
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um, 60fps and 1/60 shutter? You should be at 1/125 shutter.

This is my favorite patch and I use it exclusively.
 
balazer said:
Why? Video cameras normally use a shutter speed of 1/60 s. The 180-degree shutter "rule" is for cameras that shoot at 24 fps.
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that's not true-my understanding is the 180 degree rule applies to the frame rate you're shooting.....so 1/125th(the gh doesn't shoot at 1/120) would be preferable at 60P.....
so i'm thinking you got bad results because you used the wrong shutter speed?? also, if you go higher than about 1/250, you start to dramatically drop the data rate as well.
 
I've tested at higher shutter speeds and it doesn't correct the problem with the long GOP.

Professional television cameras for 60p and 30i are usually shooting with the shutter turned off, which amounts to a shutter speed of 1/60 s. But don't take my word for it. Go to any television production forum and read people's recommendations for shutter speeds. Run your own tests and see how the video looks at different shutter speeds. There is no hard and fast rule about shutter speeds in video. To my eyes when shooting 60p, 1/60 s looks the most natural. Sometimes people like the effect of a faster shutter, but 1/60 s is the default.

The 180-degree shutter "rule" is something from the film world, and I believe that it is misapplied when used for 60p video. You certainly can use a 1/120 s shutter speed if you are going for a certain effect, but doing so has consequences. It introduces temporal aliasing, and makes the motion integration match the way the human eye works less closely. You'll be throwing away half of the light, which forces you to use a wider aperture setting, higher ISO setting, or a faster lens. And if you ever want to upload your video to YouTube or Vimeo, it will be converted to 30p with an effective shutter angle of 90 degrees. When you shoot 60p with a 1/60 s shutter, converting the video to 30p results in an effective shutter angle of 180 degrees, with the frame rate, shutter speed, and shutter angle being somewhat close to what we are used to seeing with film shot at 24 fps.
 
60p uses a normal shutter speed pf 1/60th. 1/125th is only used if it is intended for slow motion. If you actually want to shoot 60p and playback 60p which is a broadcast spec then the normal shutter is 1/60th. It is the same rules as interlaced footage. 60i uses a normal shutter of 1/60th. Yes you have 30 frames but you have to think of interlaced as 60 fields and not 30 frames. So those 60 moments in time still use a normal shutter of 1/60th just as you would with 60p. No difference between 60i and 60p except 60p is cleaner if you were to compare at the same resolution. The motion signature is the same.
 
Here an interesting article on 180 degree shutter, and why shooting at 360 degree shutter(1/60th for 60P) is not desirable-watch the video at the end, and see if the video you are shooting with this patch looks like their example;
http://blog.tylerginter.com/?p=385
While you are correct, that originally 180 degree was used in film days-to allow the next frame of film to load, and to produce "film" look while shooting digital at 24P, if you look at the different video's, and as you shoot more video with your GH1, you will come to the conclusion-like I did(and virtually every other "film maker" on this site), that 180 degree shutter works the best for almost all situation, except when you want that "staccato" look, for doing slow-motion, the live action look.

If you want to shoot at 1/60th for 60P, then this hack is not for you. Basically, you don't need a hack-just use the original firmware-because you will end up with "mud" with any firmware you chose. "Breaking" the 180 degree rule, is something you almost never do-and certainly never to 360 degree shutter. Maybe to 72degree's, or even less, for slow-motion, or the "saving private ryan" thing...but that's about it.
My shutter stays "locked" on 180 degree's(actually about 172 degree's with the GH1-1/50th or 1/125)-and if I intend to do slow-motion, I will increase the speed of the shutter just for those shots.

There are many pages of posts on here debating the 180 degree shutter "rule"-the search function is your friend. I would also suggest you read the GH1 section, especially as it pertains to hacks. Because the problem you are having now, with this hack, has been well discussed in a lot of early posts, and I see no need to re-visit this subject for the 10th? time.
Good luck to you.......
 
http://www.dvxuser.com/V6/member.php?70965-havasuphotohavasuphoto,

I won't repeat everything that I already said, but I think you're wrong on every point. And you seem to be confusing motion blur with mud. Mud is an artifact of overcompression, when all of the high frequency details get removed from an area of the picture. Increasing the bit rate decreases the mud, at any shutter speed.
 
@balazer, I have been using this hack for two days now in low light, in SH mode at 50fps rather than 60fps and I'm not getting anything like the pulsing in your video, at 800 ASA and in poor light. I wonder why it is that you are getting the results you are when nobody else is reporting them...? Surely there are some real pixel peepers in this community, and yet nobody else has reported what you have, that I am aware of...
 
No idea. My results should be easy to duplicate, once you know what to look for. Maybe there is some difference between 60 fps and 50 fps. test.
 
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LPowell, upon investigation, I see that in the first post you state this:
75Mbps AVCHD 1280x720 SH mode @ 50/60 fps
While the unhacked 720p50/60 SH video mode offers high frame rates, its low 17Mbps maximum bitrate and long-GOP frame compression hamper its ability to track fast-moving subjects. In 60p mode, this patch reduces the length of each GOP to 20 frames, producing 3 key-frames per second. In addition, the codec's 75Mbps peak bitrate allows it to encode a large amount of image detail into each key-frame. Compression efficiency remains high enough, however, to limit average bitrates to less than 50Mbps.
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...but I have just checked in PTool, and for 720p60, the GOP length is 30 original and 25 modified, not the 20 modified you suggest in your first post. Is this an oversight, or what? Could this be the issue balazer? The GOP for 720p50 is un-modified at 26

Many thanks
Lucas
 
Lucas Adamson said:
LPowell, upon investigation, I see that in the first post you state this:

...but I have just checked in PTool, and for 720p60, the GOP length is 30 original and 25 modified, not the 20 modified you suggest in your first post. Is this an oversight, or what? Could this be the issue balazer? The GOP for 720p50 is un-modified at 26

Many thanks
Lucas
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I posted the same thing in post number 10 and lpowell probably missed it so i made the changes in my patch anyway, eighth line down in my post.
http://www.dvxuser.com/V6/showthrea...ch-V2-update&p=2382178&viewfull=1#post2382178

Probably lpowell could confirm which it is that was optimized, the GOP in the first post text or the GOP in the Patch ini.
 
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Lucas Adamson said:
I have just checked in PTool, and for 720p60, the GOP length is 30 original and 25 modified, not the 20 modified you suggest in your first post. Is this an oversight, or what?
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Thanks for spotting this documentation error Lucas, I just now corrected it in the initial post. The GOP size in the original version of this patch was 20 frames and I neglected to update that detail when I revised the docs for the V2 High Reliability Patch. I did indeed find that a GOP of 26 frames performed more reliably than shorter GOP-lengths in 720p60 mode. For 720p50 mode, the original 25-frame GOP did not need adjustment for the V2 patch.

As to the issue of shutter speed at 50/60fps, my experience tends to back up Balazer's view. The "180-degree rule" was developed in the film era for use with camera frame rates of around 24fps. It dictates a 1/48-second shutter speed that produces a cinematic amount of motion blur. In general, I find that shutter speeds in the range of 1/45 - 1/60 second look natural to my eyes, and that faster speeds look too choppy, regardless of the frame rate. As Balazer explained above, the only time a higher shutter speed is desirable is when shooting slow-motion footage at 50 or 60fps, since it will later be slowed down to a more reasonable shutter speed.
 
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