MEGUI High@L4.1 Reference Frames 5?

[bokbokchui]

I got some 1080p mkvs. When checking with MediaInfo, it shows:

Format Profile: High@L4.1
ReFrames: 5

I tried to use MEGUI to encode a mkv from a .ts source. using the followings:
Tuning: Default
AVV Profile: High Profile
AVC Level: Level 4.1
Target playback device: Default

No matter I use MEGUI advanced option (Reference frames = 5) or custom command line (--ref 5), I can't produce a mkv with High@Level 4.1 and ref. frame 5.


Even if I change the Encoding mode, bitrate, preset speed, it seems the resulting resulting frame is ALWAYS 4 and it seems bound to AVC level.


Can I produce a .mkv with High@L4.1 and ref. frame 5, similar to the 1080p mkv got from HD forum?


Bok

[sneaker_ger]

For 1920x1080 pixels 4 ref frames are the maximum allowed at level 4.1. If your movie has black bars you can crop them though, to e.g. 1920x800 for a 2.40:1 movie. Then more ref frames are allowed while staying within the level 4.1 limits.
It is possible to force the encoder to write "level 4.1" into the bitstream, while in reality exceeding that limit, but it is HIGHLY discouraged. All you will get is a broken stream which will produce errors or not work at all in many players for what is probably a negligible increase in compression (and increasing ref frames is not the only way to increase compression anyways).

[bokbokchui]

I paste the MediaInfo HTML output. It's High@L4.1 with 5 Ref. frames.

General
Unique ID : 211413123791290144127504225877586125065 (0x9F0CAFC35A847331A9DE6B70DEB0A109)
Complete name : D:\Kara.Best.Clip.II.Show.2011.BluRay.EP03.Back.Stage.&.Making.Live.at.YOKOHAMA.ARENA.1080p.AC3.x264-HDS.mkv
Format : Matroska
Format version : Version 2
File size : 1.51 GiB
Duration : 23mn 48s
Overall bit rate : 9 086 Kbps
Encoded date : UTC 2012-04-05 17:53:28
Writing application : mkvmerge v5.4.0 ('Piper') built on Mar 10 2012 13:34:39
Writing library : libebml v1.2.3 + libmatroska v1.3.0

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.1
Format settings, CABAC : Yes
Format settings, ReFrames : 5 frames
Codec ID : V_MPEG4/ISO/AVC
Duration : 23mn 48s
Bit rate : 8 730 Kbps
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate : 29.970 fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.140
Stream size : 1.41 GiB (93%)
Writing library : x264 core 120 r2164 da19765
Encoding settings : cabac=1 / ref=5 / deblock=1:-3:-3 / analyse=0x3:0x113 / me=umh / subme=8 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=20 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=0 / chroma_qp_offset=-2 / threads=24 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=6 / b_pyramid=2 / b_adapt=2 / b_bias=0 / direct=3 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=50 / rc=2pass / mbtree=1 / bitrate=8730 / ratetol=1.0 / qcomp=0.70 / qpmin=0 / qpmax=69 / qpstep=4 / cplxblur=20.0 / qblur=0.5 / vbv_maxrate=14000 / vbv_bufsize=14000 / nal_hrd=none / ip_ratio=1.40 / aq=1:1.00
Language : English
Default : Yes
Forced : No

Audio
ID : 2
Format : AC-3
Format/Info : Audio Coding 3
Mode extension : CM (complete main)
Format settings, Endianness : Big
Codec ID : A_AC3
Duration : 23mn 48s
Bit rate mode : Constant
Bit rate : 448 Kbps
Channel(s) : 2 channels
Channel positions : Front: L R
Sampling rate : 48.0 KHz
Bit depth : 16 bits
Compression mode : Lossy
Stream size : 76.3 MiB (5%)
Default : Yes
Forced : No

It's 1920x1080 without any crops. High Profle@Level 4.1

Do you have any hints how it's created? Are they using methods other than MEGUI to create this mkv?

[sneaker_ger]

That file does not comply with AVC level 4.1. As I've said: it's no problem writing "level 4.1" into the bitstream, while it is in reality exceeding the level 4.1. I can use 16 ref frames and write "level 1.0" into the file. That does not make it level 1.0!
MeGUI seems to not allow that - for good reasons. I could tell you how to do it, but that would be just stupid.

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

[bokbokchui]

I'd appreciate if you could tell me the 'stupid' method. Just for a reference of learning

[Zathor]

MeGUI takes care about inappropriate settings. If you want to have a higher ref value you have to choose a higher level (or unrestricted).

[KafesneBikaina]

What is the max RefFrames for 1280x720 at level 4.1?

[sneaker_ger]

That would be 9. If you set "--level 4.1" (but not also "--ref") x264 will automatically limit the number of ref frames so that the limit will not be exceeded, btw.

[Thunderbolt8]

sorry for the bump, why is it possible to have 1 more reference frame without black bars? The file is still L4.1 BD compliant then?

[trumpet205]

At 1920x1080, 4 reference frames is the max to stay within Level 4.1. Period.

As said, you can specify both level 4.1 and 5 reference frames on the settings. You essentially tell x264 to jot down level 4.1 on bitstream despite being not 4.1 compliant. That does not mean the encoded file is level 4.1 compliant, it is NOT. In fact, most consumer player cannot deal with H.264 greater than level 4.1.

[Thunderbolt8]

so what about that?

Originally Posted by sneaker_ger

For 1920x1080 pixels 4 ref frames are the maximum allowed at level 4.1. If your movie has black bars you can crop them though, to e.g. 1920x800 for a 2.40:1 movie. Then more ref frames are allowed while staying within the level 4.1 limits.

[trumpet205]

Because cropping means cutting borders away. Your display resolution now has gone smaller.

Smaller resolution means it takes less space in memory buffering. Level of H.264 is an indication of memory requirement.

Higher resolution or higher number of reference frames is more demanding. So when a resolution goes smaller you have more headroom for number of reference frames.