Blu-ray compliancy (x264): Number of B-frames?

[moviefan]

Hi everyone,

I've had a look at the Blu-ray profile in meGUI and saw that the max. number of B-frames is set to 3 as well as the max. number of reference frames. Is this the absolute limitation for a 1080p Blu-ray video?

[meisterlee]

Max. B-frames 3 (H.264)
Max ref frames 4

[moviefan]

OK, when already talking of this, do you know the specs for the said settings for 720x576p/i (whether p is possible is discussed in another thread)?

[Sagittaire]

Originally Posted by meisterlee

Max. B-frames 3 (H.264)
Max ref frames 4

For 4.1 level it's:
1/2/3 bframes without pyramidal bframe: 4 pref and 3 bref
3 bframes with pyramidal bframes: 3 pref and 2 bref

--bframe 1/2/3 --ref 3
--bframe 3 --b-pyramid --ref 2

[moviefan]

That's easy to understand, thanks Sagittaire! Comparing the variants you suggested, when should I use the first and when the second settings?

[Sagittaire]

--bframe 3 --b-pyramid --b-rdo --ref 2
really efficient for clean source and/or low motion

--bframe 1 --ref 3
3 bframes with noise/grain is useless

Anyway if bframe decision is good the encoder will never use in practice 3 pyramidal bframes with grainy/noisy source.

[moviefan]

@Sagittaire: Hm, weird, is it definitely fact that using pyramidal bframes limits the number of reference frames to 2? You always talk of a number of reference frames less than 4, while meisterlee says it was 4. I want to get the most out of x264 and thus don't care about encoding time. The source is pretty clean...

[bigotti5]

is it definitely fact that using pyramidal bframes limits the number of reference frames to 2

No (Level 4.1 does not, dont know for x264)

[moviefan]

So I could use

--bframe 3 --b-pyramid --ref 4

for a clean source and should get best quality as for these settings + Blu-ray compliancy?

[blizzbit]

Here are the settings of Elecard Converter Studio full quality profiles:

Blu-Ray:
B-frames: 1
Ref. frames: 4

Blu-Ray HD:
B-frames: 2
Ref. frames: 4

Use B-frames as reference/Pyramid coding is disabled for Blu-Ray SD and HD.

How about these settings?

[Trahald]

For some reason when I use ref = 4 i get jumpiness (thats with x264 or cinevision), but thats only with cyberlink and my 8500 (dont have standalone) ref = 3 works better. having said that...

bluray spec is max 3 b-frames and b-pyramid (in conjunction is 3 b-frames) is allowed. ref = 4 is correct to L4.1 w/1080p.

so in spec.. yes.

[blizzbit]

Thanks, Trahald.

Does this mean that...

with Pyramid coding
B-frames: 3
Ref. frames: 3 (for more compatibility, otherwise 4)

without Pyramid coding
B-frames: 1
Ref. frames: 3 (for more compatibility, otherwise 4)

If I set 2 or 3 B-frames here, I get the following AVC encoder message (Elecard Converter Studio):

2 B-frames: "It is recommended to use one B-frame or three B-frames with the following options for encoding: 'Adaptive B-frames', 'Use reference B-frames' and 'Pyramid coding'"

3 B-frames: "For encoding with three B-frames the following options must be enabled: 'Adaptive B-frames', 'Use reference B-frames' and 'Pyramid coding'"

What amazes me is that XolocoTuxmaster recommends 3 B-frames and 3 Ref. frames for Blu-ray encoding without B-Pyramids.

Originally Posted by XolocoTuxmaster

Preparing the video

With the nal_hrd patched x264 version, we use our favourite line/profile to encode the video, not forgetting these parameters in the final line:

--keyint 24 --min-keyint 1 --vbv-maxrate 38000 --vbv-bufsize 30000 --nal-hrd --mvrange 511 --level 4.1 --bframe 3 --ref 3 --aud --sar 1:1

And forgetting:

--b-pyramid

Source: Quick Blu-ray content (BD, BD-5 and BD-9) authoring guide (PS3+PowerDVD)

[Trahald]

you know what.. i did the math using the spec.. and i may be wrong.. but i get that 3 would be max... here is the math

min( 1024 * MaxDPB/(PicWidthInMbs * FrameHeightInMbs * 384), 16)
1024 * (11288) / (120 * (( 2 – frame_mbs_only_flag ) * PicHeightInMapUnits) * 384)
1024 * 11288 / (120 * (( 2 - 1 ) * 68 ) * 384 )
1024 * 11288 / (120 * ( 68 ) * 384 )
11558912 / (3133440)
3.688888888888
min(3.6888,16) = 3.368888

so 3 would be max (num ref frames / max dec frame buffering).. weird

[bigotti5]

... here is the math

something wrong...

Specification lists for Level 4.1:
Picture Buffer 12288 kB (12582912 Bytes)
Max MBs 8192 (1920x1088 -> 8160 Macroblocks)

so
8192 (=Macroblocks) x 256 (=pixel per macroblock) x 1.5 (= 4:2:0 video uses 12 bit per pixel = 1.5 Byte)
8192 x 256 x 1.5 = 3145728
12582912 / 3145728 = 4
Level 4.1 certified Decoder can hold 4 Ref. Frames

[Sagittaire]

Well in fact it's 4 pref and 3 bref for level 4.1 but x264 use the same value for pref and bref. If you use pyramidal bframe you must use 3 pref and 2 bref.

imply for x264
--bframe 1/2/3 --ref 3
--bframe 3 --b-pyramid --ref 2

Other setting are not BluRay compliant.

[Dark Shikari]

Originally Posted by Sagittaire

Well in fact it's 4 pref and 3 bref for level 4.1 but x264 use the same value for pref and bref.

No it doesn't. It hasn't done this for months. If you set --ref 4, it'll use 4 Prefs and 3 Brefs.

[blizzbit]

Hmmm... one noob question... where is difference between the MaxDPB (max decoded picture buffer) and MaxCPB (max VBV buffer)?

[Sagittaire]

Originally Posted by Dark Shikari

No it doesn't. It hasn't done this for months. If you set --ref 4, it'll use 4 Prefs and 3 Brefs.

good news ... so it's:

imply for x264
--bframe 1/2/3 --ref 4
--bframe 3 --b-pyramid --ref 3

[Trahald]

oops.. i copied the MaxDPB value wrong from the table.. here is the revised calc

min( 1024 * MaxDPB/(PicWidthInMbs * FrameHeightInMbs * 384), 16)
1024 * (12288) / (120 * (( 2 – frame_mbs_only_flag ) * PicHeightInMapUnits) * 384)
1024 * 12288 / (120 * (( 2 - 1 ) * 68 ) * 384 )
1024 * 12288 / (120 * ( 68 ) * 384 )
11558912 / (3133440)
4.0156862745098039215686274509804

so 4


but weird i see pro streams (streams that have are tweaked out different PPS settings per picture and adaptive inloop filter levels per frame etc) using 2 and 3 refs. i suppose its knowledge the hardware that should be able to handle it cant?