High frame rate UHD lossless, can you view it?

[Boomhowler]

Hi!

I'm currently evaluating what hardware that is needed to run a high bitrate, 50 fps 2160p (3840x2160, UHD, 4k, what you want to call it) encoded with either ffv1 or h264-lossless. I tried it on several computers, both OS X and windows (and linux) and nothing I've encountered yet have managed to play it out even on 24fps.

The encoded bitrate (using ffmpeg with llv1 or libx264 -crf 0 or 1, with -pix_fmt yuv420p so it is chroma subsampled.. "easy" ) is more than 2 Gbps, so quite taxing.

If someone would like to try it I could provide you with either the encoded file (~3GB) or a link to the online .png-files with command line encoding settings.

 

[joema2]

2 Gbps is 250 megabytes/sec -- not including any OS I/O, file system overhead, and assuming Time Machine, Spotlight Indexing and nothing else is running on that volume. However that is within reach of a fast disk array.

But hardware capability means nothing if the playback software does not fully harness that and manage all system resources required for smooth playback. E.g, it might require issuing overlapped I/Os to build up a queue so the disk subsystem is fully utilized. It also might require allocating very large memory buffers and careful management of buffer logic in the playback software, and multithreaded handling of the disk requests, incoming data, H264 decoding, display processing and user inputs. Testing of that software would require close attention to latency at multiple points when reading, processing and displaying that data stream.

Even if the I/O can be handled, likely a bigger problem the H264 encoding -- albeit intraframe. It must be decoded at an incredibly high bit rate. E.g, Youtube recommends 58-68 Mbps for 4k uploads, so you're talking about 30 times that rate.

If you are developing a database server you devote extensive design and testing priority to items like that. Maybe the people writing VLC, Quicktime Player, etc. don't design or test extensively for those conditions, except for ProRes. Or maybe the hardware itself can't handle it or it might require Quick Sync acceleration for playback. FCPX uses Quick Sync for decode/encode, but maybe VLC/Quicktime Player don't use that or maybe Quick Sync can't handle intraframe H264 with those encoding parameters, which would drop you down to software-only decoding.

That said, I exported some 4k content from FCPX using uncompressed 10-bit 4:2:2, producing a 5.3 Gbps bit rate. QuickTime Player seemed to play it OK from the SSD drive of my top-spec 2015 iMac 27. It also played smoothly that same content exported as ProRes 4444HQ, which is 1.4 Gbps. But all these cases uses either no compression or visually lossless compression (ProRes 4444HQ).

I am guessing the H264 decoding code path in your playback software is either not optimized for this case or the hardware cannot handle the decoding at that rate.

I would try your clip but I don't want to download a 3GB file. Is there any way you can provide a smaller sample?

 

[Boomhowler]

You are absolutely right that it's a bit much hoping that a "normal" computer using VLC or similar "consumer" software would be able to play it smoothly, but I want to try some different setups before we start buying blackmagic-cards etc.

The clip is only 10s long but I can probably get it down to ~ 1GB by only using a third of it. I'll post a link when it's done

I tried encoding the images with pro-res (both 420HQ and 4444HQ) and it ran butter smooth on my MacBook Pro. There are two problems with the prores format though;
1) it is not openly described so the ppl I'm working with from other organizations and companies do not trust Apples "visually lossless", especially for video samples that we are going to use as hidden reference in subjective quality assessment.
2) when viewing the clip on a "standard" pc it is not any smoother than using ffv1 or h264-lossless for the same reasons as you describe above. VLC in windows don't have the same connection to the hardware as QT on the Mac has, when using prores.

Thanks for the comments btw!

 

[Boomhowler]

I've sent you a pm with the link. If anyone else wants to try it, write here so I can pm you the link as well.

 

[joema2]

The MKV file would not play smoothly on my 2015 top-spec iMac using Quicktime Player or VLC, nor on my 4Ghz Windows PC using VLC or Windows Media Player. It wasn't just laggy but included intermittent frames of video garbage.

...I tried encoding the images with pro-res (both 420HQ and 4444HQ) and it ran butter smooth on my MacBook Pro. There are two problems with the prores format though;
1) it is not openly described so the ppl I'm working with from other organizations and companies do not trust Apples "visually lossless", especially for video samples that we are going to use as hidden reference in subjective quality assessment.

ProRes 4444 is used to make major Hollywood movies. ARRI Alexa supports ProRes 4444XQ: http://www.hollywoodreporter.com/behind-screen/arri-alexa-upgrade-supports-prores-715756

It would be interesting if they could reliably pick the difference in a blind A/B test between the same content encoded as ProRes 4444XQ vs h264-lossless.

....when viewing the clip on a "standard" pc it is not any smoother than using ffv1 or h264-lossless for the same reasons as you describe above. VLC in windows don't have the same connection to the hardware as QT on the Mac has, when using prores.

Yes this is an issue, not only the playback performance but whether it will play at all and what playback codec is needed. On my 4Ghz PC, the high bitrate ProRes codecs won't play at all in VLC or anything else. There is probably some codec pack that would play them but I don't have time to investigate that.

On my 2015 iMac VLC won't play a 4444XQ file but it will play smoothly an uncompressed 10-bit 422 file. On my PC VLC will play that file but not smoothly.

This issue is more than just hardware but what combination of playback software and hardware are needed. If they are willing to accept some other codec, QT Player on MacBook Pro will play a 4k 2 Gbps ProRes 4444XQ file or even a 5 Gbps 10-bit lossless 422 file.

If they want a codec and playback software that works on both Mac and PC at that extreme bit rate, that will be a research project to determine what codec, playback software and Mac/Windows hardware are required.

 

[Boomhowler]

Thanks for the help with the testing. We ended up buying a Blackmagic-card and a bunch of pci-ssds It works great.

And yes, I inspected several frames from a bunch of films to find differences between Prores4444xq and the lossless pngs. I would definitely say that they are visually lossless and any PSNR or similar measurements show the same results.