What is the difference between x264 AVC High@L5.1 and High@L4.1?

[Bonie81]

What is the difference between x264 AVC High@L5.1 and High@L4.1?
Which one gives better quality?

[redwudz]

L5.1 appears to use four to five times the bandwidth of L4.1 and looks to be for very high definition video, 4096×2304@25 or similar. You might take a look at this article as it seems to have a lot of information on the different levels: http://rob.opendot.cl/index.php/useful-stuff/h264-profiles-and-levels/ L5.1 would probably give better quality, but you would need a source video at that quality and a program or device capable of playback. Maybe this type of source:

[jagabo]

http://en.wikipedia.org/wiki/H.264/MPEG-4_AVC#Profiles

[poisondeathray]

Note it just sets an upper limitation. It doesn't mean one is better.

The actual content and settings used might actually be lower. eg. Some people set it to read L5.1, but the actual contents might conform to only L4.0

[Bonie81]

@ redwudz, jagabo, and poisondeathray

folks thanks for the inputs.
jagabo, wiki link is informative.

Thanks!

[Splash fanboy]

you guys forget about reference frame buffer,
level 5.1 allow to more than 4 reference frames for 1920x1080, which means encoder can save some bitrate and achieve better quality using more reference frames (i.e. 8, 10, 16).
But in the other hand, not all hardwares/softwares support AVC level 5.1. for example ATI hd 2xxx or 3xxx does not in DXVA.

[jagabo]

I suspected there was a difference in number of reference frames, and probably then number of consecutive b frames too, but couldn't find a definitive-ish reference. The use of more than 4 reference frames rarely makes much difference though. If you look at the encoding logs you'll see 4 or less used 99 percent of the time.

[Splash fanboy]

but he asked: Which one gives better quality?
the answer is: 5.1

[Atak_Snajpera]

This is just a label for god sake! It is just a basic information for decoder. Each level has limitations (http://en.wikipedia.org/wiki/H.264/MPEG-4_AVC#Levels) . To be honest level 4.0 should be enough for everybody. 25Mbps is ALOT for good h.264 implementation like x264. Some noobs still think that level means automatically better quality (4.0 < 4.1 for example)

[jagabo]

Of course, H264 Level Editor only changes the profile flag in the header. If the video actually has High@5.1 properties it won't play properly on players that only support High@4.1.