Level 4.1 vs. 5

[Anakunda]

Hello, what essentially is the difference between Level 4.1 and 5, ie. is 5 better that 4.1, and why are all HD videos encoded to Level 4.1 when encoder (x264) sets default for HD to Level 5 or higher? I guess it may something to do with hw players compatibility, if so - is the Level 5 so few supported on HW players manufacturers?

[sneaker_ger]

http://en.wikipedia.org/wiki/H.264#Levels

In short: yes, level 4.1 has higher hardware compatibility. Because Blu-Ray uses (a subset) of level 4.1, that's what many devices are developed for. Higher levels would allow for more bitrate (irrelevant to most consumers) and more reference frames (though these can supposedly be useful, especially for animated content, the cost is not that high.).

[Anakunda]

http://en.wikipedia.org/wiki/H.264#Levels

In short: yes, level 4.1 has higher hardware compatibility. Because Blu-Ray uses (a subset) of level 4.1, that's what many devices are developed for. Higher levels would allow for more bitrate (irrelevant to most consumers) and more reference frames (though these can supposedly be useful, especially for animated content, the cost is not that high.).

What you mean exactly by more reference frames? If thats the --ref I see its set to max 16 regardless of level. Does it mean that Level4.1 doesnot use all 16 ref. frames ?
And if the 4.1 limitation deals with BluRay players mostly, then do most home media centers and HD TVs which are not determined for playing BluRay discs, support Level 5?

[nurbs]

If you set --ref manually x264 will use whatever you set even if it breaks the --level you set. If you only use presets and tunings the level will limit the reference frames.

[benwaggoner]

Honestly, I do most of my 1080i/p at Level 4.0. The lower peak bitrate of 25 Mbps is still more than ample, and Level 4.0 doesn't need slices in Blu-ray, and so is more likely to be compatible with random decoder ASICs.

The VBV/peak bitrates allowed by the H.264 levels are quite generous, particularly at High Profile. I generally use the lowest Level compatible with the frame size/rate I'm using. This increases compatibility, and almost never has a visible quality hit.

There a lot of device limitations based on Level; many handsets only do up to Main or High Level 3.0, and iPad only does up to Main Level 3.1. So been conservative on Level offers a lot more playback flexibility.