F55: Pushing XAVC too far?

G

Gizmosgadget

Active member
Hello all.

I think I broke XAVC with my F55. I was shooting some fall foliage in 4K XAVC300 24P and noticed some really nasty macroblocking not only in the leaves but also the blue sky. I figured I just stretched the codec more than I should have. It's the first time I've noticed this in three years. I probably would have been better off shooting this in SR. Does anyone else have any experience with XAVC not holding up under certain situations?

Cheers

Craig
 
Sounds like a good (i.e. difficult) "challenge test". 4K or 1080p? My experience with the FS5's 4K (well QFHD to be correct) 100Mbps XAVC Long GoP (so far) in WYSIWYG type scenarios is that it is remarkably robust. Amazingly good...unless you try and really "stretch it" in post.

Any chance of seeing a short example clip?
 
I've seen it once in a very controlled lit environment. In HD xavc 24p, Custom mode, HG3, Cinema matrix, about ISO 1250 or 1600. Was in a 30x30' room that had a 3' tall solid grey stripe across the wall and was awash with light. I was on sticks with some subjects in the foreground with exposure on foreheads around 60 IRE. When reviewing the footage I saw whole sections of the grey stripe macro blocking. It was totally bizarre and couldn't put my finger on why. The grey area was probably around 50-40 IRE. Have never seen it otherwise in three years on my F5. If I had the footage still I'd post a grab but it's long gone.
 
Here's a dropbox link.

https://www.dropbox.com/sh/343w16am1dl33pv/AAADWjBvouFhfjhPkOhpEP9Ya?dl=0

The clip is a 4k XAVC file around 5 seconds long, 150MB. I was shooting S-log3/S-gamut3.cine, mid grey around 50, ISO 1250. I applied the LC709A lut in RAW viewer, made some tweaks and rendered the file. There are compression artifacts on the top left and right of the image. Hard to miss them. They are visible within RAW viewer, not just the rendered file. I went and looked at some other footage of foliage I shot a month ago and saw a similar thing. Let me know what you think.

I've just added the same clip but with no color correction applied. Straight out of the camera just trimmed down to 5 seconds.
 
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Resolve is definitely cleaner. Not perfect, but much better. Thanks for recommending that. I use RAW viewer for quick turnaround stuff and don't use Resolve very often. I may have to change that. I'm not using this particular footage for anything, I was just surprised and wanted some feedback. Thanks everyone.

Craig
 
Apologies, I just realised in my hasty reply that I misstook F55 for FS5...damn you Sony for releasing so many cameras with similar product codes...
 
Unfortunately, this may happen to the otherwise great XAVC-I codec quite easily sometimes. Just see my own thread here:
http://www.dvxuser.com/V6/showthread.php?346566-nasty-artefact-on-clear-blue-sky-with-FS7-kit-lens

But don't be fooled by the thread title - after long investigation, what I called a "thin white line across blue sky" and suspected to be the particular lens or the imager going bad, turned out to be exactly what you're describing: compression-related macroblocking. People on this forum (as well as on other boards, and the Sony PrimeSupport) kept telling me it's normal; later they attributed it to my grading the 10-bit Slog footage in the 8-bit editing suite. But after switching to Resolve I am now 100% positive it was the codec breaking... What's worse, I didn't inflict it by stretching the codec too much at grading - it's there in the original footage! Beware - the "300" version of XAVC is actually very prone to this kind of failure, especially when shooting UHD/4K at 24/25 fps meaning only some 2xx Mbps bitrate! It almost never happens to me when shooting at 50 fps when datarate is ca. 500 Mbps - and this is why the new "480" version which is coming to F5/55 would be such a welcome addition to the FS7, as well...

Piotr


Gizmosgadget said:
Hello all.

I think I broke XAVC with my F55. I was shooting some fall foliage in 4K XAVC300 24P and noticed some really nasty macroblocking not only in the leaves but also the blue sky. I figured I just stretched the codec more than I should have. It's the first time I've noticed this in three years. I probably would have been better off shooting this in SR. Does anyone else have any experience with XAVC not holding up under certain situations?

Cheers

Craig
Click to expand...
 
XAVC favours detail and motion at the cost of heavily compressing flat luma areas.

This image below has a tight keyed colour correction on the sky to show the underlying compression posterisation. The tree leaves were gently blowing in the breeze so there was a lot of detail and motion in the image that this crop is taken from.

I've tested the codec with seas and trees against flat skies and both show the similar result that the trees blowing in the wind and the waves of the sea retain detail while the sky is crunched like the image below.

I was extremely disappointed with these results from my FS7 as it was a bit of a dirty secret of XAVC but actually in practice it doesn't cause a huge issue. Crappy LUTs, poor technique can bring these compression artefacts to the fore sooner. Resolve's keyer is very clever and is able to take a wide sample and when you correct the sky it holds together better than other solutions.

When I'm shooting a scene with a sky I try and get as much sat into the sky with a good quality polariser so I don't have to do it in post. I'd like to test a ProRes recorder on a side by side scene and see if ProRes does a better job of the sky, I suspect it will or at least produce less mechanical looking artefacts that are less ugly.

I think Sony made a clever choice with XAVC despite the sky limitations as XAVC captures the motion and the detail for a very reasonable file size where other compression schemes trash detail and motion from the start and then it's trashed again by the broadcast codec. At least with XAVC the detail and motion is only trashed by the broadcast codec.

2yuaosm.png
 
Yep I think there is no free lunch.

Im on 70TB mainly shot in the last two years.. if that had been raw it probably been 700TB.

It seems the 'cost' of saving that 630TB is occasionally some crappy smooth tones when other parts of the image are rammed with detail.

S
 
Nirv said:
XAVC favours detail and motion at the cost of heavily compressing flat luma areas.
Click to expand...

Bingo. This makes perfect sense re: what happened to me with my solid grey stripe on the wall. Everything else with varying tones was "moving" and detailed but the constant flat luma of the stripe made the codec single it out and over compress it. Disconcerting but again a very extremely rare occurrence.
 
XAVC is a super efficient codec, it's one of the great things about it. But it's a pretty high compression ratio.

If you want the best quality the cameras can output without a raw recorder, then SR444 is the way to go in my experience. The new XAVC480 might start to match it, we'll just have to wait and see.
 
Fotojorno said:
Bingo. This makes perfect sense re: what happened to me with my solid grey stripe on the wall. Everything else with varying tones was "moving" and detailed but the constant flat luma of the stripe made the codec single it out and over compress it. Disconcerting but again a very extremely rare occurrence.
Click to expand...

Once you know how the codec works you start to anticipate potential post production issues and mitigate them.

I'm very interested to see what XAVC-I 480 looks like and hope that will come to the FS7 if not I'll try a cheap ProRes recorder for those times where a different compression scheme may be better suited.
 
Nirv, I pushed the grade with my footage and saw the exact same thing. Other than this XAVC has been great. I haven't had the chance to test out 480 yet, but the leaves are all gone now. :)
 
Yeah... Even though I'm in the market for a HDR-capable field & studio monitor, and - with SmallHD 1303 HD being too expensive - have been thinking about the new Shogun Inferno, which would also offer DNxHR HQX recording, I'll wait to see whether the XAVC 480 will be added to FS7. If it does, the recording functionality of Inferno would probably become redundant (still though, the Inferno will not be excluded as the only HDR monitor apart from the ridiculously expensive 1303)...

Piotr
 
I shoot a lot of foliage and havn't run into this since the AF100. Had the FS700, now have the FS7, have shot all codecs with no issues with foliage.

When I'm shooting a scene with a sky I try and get as much sat into the sky with a good quality polariser so I don't have to do it in post. I'd like to test a ProRes recorder on a side by side scene and see if ProRes does a better job of the sky

I usually use a polarizer when shooting this type scene so seldom have to do a lot in post. Never seen a Prores /XAVC comparison where XAVC did not come out ahead, at least when it comes to macroblocking.
 
mainstreetprod said:


Never seen a Prores /XAVC comparison where XAVC did not come out ahead, at least when it comes to macroblocking.
Click to expand...

I've never seen anyone back up these sorts of statements with hard data.

ProRes is a different compression scheme to XAVC and will certainly not produce industrial slab like macroblocking of the sky in my example so what downsides there are to using it apart from filesize is still an open question until I manage to find time to hire a recorder.
 
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