What's so special about X-70 XAVC-L UHD codec?

[Piotr Wozniacki]

There's been lots of threads (here as well as on the Vegas forum) with people asking questions about the X-70 files being particularly difficult for Sony Vegas Pro 13 to handle (or - earlier on - even open in the first place). Now the discussion seems to be long forgotten, but I must admit I'm still uneasy about Vegas handling X-70 files - and not only 4K, but the 1080p flavor of XAVC, as well. Of course the hardest to Vegas decoding is the UHD Long-GOP format - I can see it clearly on my (a bit outdated PC) that - while XAVC-L files with everything else equal (bitrate, color, framerate) coming from the A-1, A-100, Z-1 or FS-7 can be played back at Best/Full quality with full framerate (well - up to 30p; my particular PC is simply too slow for 50/60p 4K/UHD from any source) - such files stutter at max 18-20 fps if they happen to originate with the X-70! Interestingly, its consumer sister's - the A-100's - files play back with solid 25fps (I'm in the PAL, or 50 Hz, region) - is it only due to less compression (100 vs. 60 Mbps)?

As some of you may know, due to my physical condition I'm getting rid of all my pimped-out HD stuff, but would love to get myself a small and lightweight 4K camera - if only with hobby in mind... And I do have a serious dilemma here: I like all the professional features of the X-70 (the balanced mic input is enough for me to prefer the X-70 over the A-100, not to mention all those picture controls unavailable in the consumer version). But not only is the X-70 itself more expensive than its consumer sibling - the strange problem making Vegas labour when playing back even a plain clip, before any cc or fx addition - mean for me that I would have to upgrade my PC right away (yeah I know about proxy editing but hey), rather than some time in the future when I'm more ready...

Now, my simple question is this: in those numerous discussions, have people reached some consensus on what is so special about the X-70 XAVC-L codec which is so hard to swallow by Vegas? Just as many of you guys count on Sony delivering to their promise of upping the X-70 UHD bitrate from 60 to 100 Mbps, is there a chance it will become at least as easy for Vegas editing as A-100 files are?

[Bob Searl]

I don't know anything about Sony Vegas, but it stands to reason that any editor is going to have an easier time editing the file in intra-frame format as opposed to handling the unpacking and computing required to recreate the frames on any of the files presented to it as Inter-frame files. In the Sony XAVC case the Long GOP Inter files may be great for camera capture (High compression/smaller file size), but most people agree that it is best to edit either in a less compressed Intra formatted file such as ProRes or even as XAVC-Intra files (both with the .mov container)--at least for FInal Cut Pro X and the X70 files.

As a general rule, I believe that this would be true for any combination of Inter vs Intra codecs regardless of vendor. Of course, as you know, there are some who prefer to capture and edit in either an uncompressed or even RAW format. Sony already has their line of pro cameras that record directly to XAVC -Intra. The X-70 is placed below that market---where smaller files are desirable. These smaller files can easily (UGH! Cough!) be transcoded into their cousins, XAVC-Intra, and imported to the NLE for editing.

Sony believes that the XAVC-Long GOP offers superior compression which directly translates to enable lower bit rates and smaller files---which they feel is the appropriate target for the X70 market. They have suggested that this is accomplished without noticeable quality loss as it passes along the workflow pipeline. I think that they see the lower bit rates which significantly reduce files sizes at equal quality as a plus, not a minus.

In the case of the 4K frame sizes, that changes the equation---it ups the bit rate requirement vis-a-vis 1080p. They have also had to compromise the color depth to keep the bit rate (and therefore file size) low(er) for the X70 market. Improvements in their chips or compression algorithm may ultimately allow them to do the 4K for the X70 at 10 bit color depth without paying to high a price in bit rate...but until then they may feel pressure to up the color depth and therefore the bit rate---which they may have to do if the market demands it.

The market will determine if they are successful or not.

[Piotr Wozniacki]

Thanks for your answer, Bob.

What you haven't addressed (or I didn't express properly in my poor English) is that I'm comparing the X-70 XAVC-L samples to the same codec (specifically, also Long GOP) from other cameras - and for some reason, the x70 will always play back the worst.

[Peter Wright]

How bad is your timeline playback Piotr?

I upgraded my x70 to 4k this morning, and my first clips playback reasonably in Vegas.

Untouched 4k video without FX plays back 25 fps at Best/Full.

FX, dissolves or titles do slow things down, so back to Preview/Auto for editing.

My PC is 3 years old i7 3500k.

[Piotr Wozniacki]

Well Peter - my CPU is weaker than yours (2600K) - so you can imagine it's not even full 25 fps at Best/Full (while clips with the same codec but from other cameras do run at 25 fps)...

[Peter Wright]

Yes - there must be other differences between how the cameras make their clips.
I'm hoping that the x70 differences result in optimum picture quality. It certainly produces nice pictures.

[Piotr Wozniacki]

Hmm... If Sony have devised this 60 Mbps L-GOP compression algorithm for XAVC-L so that it doesn't increase compression artefacts much above those of the consumerish 100 Mbps version for otherwise identical codec as per the ax100, this would shed new light on the whole "lowest datarate in the Industry" issue and - at the same time - explain the extra work CPU must do to de-compress it while playing back the timeline...

Hence, my question to non-Vegas Pro NLEs users: do you also notice X70 XAVC--L files to create more CPU overhead than long GoP UHD codex from other cameras mentioned (A1, AX100, Z1, FS7)?

[Craig Seeman]

As a compression, it's important to understand that bit rate alone doesn't define the quality of the encode. If Sony is using CABAC entropy in this case whereas others are using CAVALC it would be possible to achieve better quality at lower bit rates. It's quite possible that Sony can't achieve 100Mbps in this case because the encoder needs more resources to get there than other lesser encoders hitting 100Mbps.


Another thread pointed out how the x70 is using CABAC whereas JVC camera was using CAVLC.

What one might do, if they have both cameras is compare the x70 vs AX100 4k recording using the free MediaInfo which would present such information about the encode.

Given the CABAC also requires more resources to decode it's entirely possible that older computers might have a harder time playing it back then compared to a CAVLC encoded file.