Welcome to Doom9's Forum, THE in-place to be for everyone interested in DVD conversion. Before you start posting please read the forum rules. By posting to this forum you agree to abide by the rules. |
7th January 2006, 05:25 | #1 | Link |
Registered User
Join Date: Mar 2005
Location: Italy
Posts: 286
|
AVC (X264) stupid questions
They are stupid question and it's a stupid topic, but can anyone try to explain me:
the -trellis switch; the no fast p skip switch (ok, it doesn't skip p frames, but why???) the psnr calculation??? Tnx Last edited by Hyper Shinchan; 7th January 2006 at 05:29. |
7th January 2006, 07:29 | #2 | Link |
Registered User
Join Date: Apr 2005
Posts: 1,740
|
Trellis does a similar sort of quantization as it does in XviD (I have no idea how it works). The effect of that is --trellis 1 (enabled only on the final encode of a MB) produces a good PSNR improvement at small speed cost, and --trellis 2 (enabled on all mode decisions) produces a small PSNR improvement on top of that, at large speed cost. Basically, it's a good idea to keep --trellis 1 for most encodes. EDIT: bond points to the results from his tests below, which show somewhat the contrary.
--no-fast-p-skip turns off fast detection of PSKIP blocks (NOT frames). Once again, I don't know the algorithmic difference, but this makes it slightly slower, but solves the blocking in flat areas issue. --no-psnr turns off PSNR calculations. These are purely informative, and there is no effect on quality from turning them off, but it does cause a speedup. Last edited by berrinam; 7th January 2006 at 13:19. |
7th January 2006, 07:53 | #3 | Link |
Angel of Night
Join Date: Nov 2004
Location: Tangled in the silks
Posts: 9,559
|
They've all been explained in the x264 dev thread and in various other threads, but...
Trellis: Gives slightly better compression of data after the encoding procedure (CABAC only) by changing what information is kept. Somewhat slow. no-fast-pskip: pskip is a code x264 uses to flag that a macroblock doesn't change at all. There are various pskip implementations; fast had a habit of detecting wrong and causing blocking in low-detail areas, though it's somewhat better now that it uses an extra check. no-fast checks every possible vector before deciding. psnr: rough metric comparing original to encoded version. Last edited by foxyshadis; 7th January 2006 at 21:29. |
7th January 2006, 12:46 | #4 | Link | |
Registered User
Join Date: Nov 2001
Posts: 9,770
|
Quote:
http://forum.doom9.org/showthread.ph...643#post733643
__________________
Between the weak and the strong one it is the freedom which oppresses and the law that liberates (Jean Jacques Rousseau) I know, that I know nothing (Socrates) MPEG-4 ASP FAQ | AVC/H.264 FAQ | AAC FAQ | MP4 FAQ | MP4Menu stores DVD Menus in MP4 (guide) Ogg Theora | Ogg Vorbis use WM9 today and get Micro$oft controlling the A/V market tomorrow for free |
|
7th January 2006, 13:21 | #6 | Link | |
Registered User
Join Date: Nov 2001
Posts: 9,770
|
Quote:
__________________
Between the weak and the strong one it is the freedom which oppresses and the law that liberates (Jean Jacques Rousseau) I know, that I know nothing (Socrates) MPEG-4 ASP FAQ | AVC/H.264 FAQ | AAC FAQ | MP4 FAQ | MP4Menu stores DVD Menus in MP4 (guide) Ogg Theora | Ogg Vorbis use WM9 today and get Micro$oft controlling the A/V market tomorrow for free |
|
8th January 2006, 01:08 | #7 | Link | |
Registered User
Join Date: Mar 2005
Location: Italy
Posts: 286
|
Thank you guys! Really useful explanations (also if ? have my doubt about trellis, for me it seems to works....).
Quote:
tnx again! P.S.: an explation thread would be useful, it could be included in the avc thread, but maybe it's off topic.... |
|
8th January 2006, 01:30 | #8 | Link |
retired developer
Join Date: Oct 2002
Location: Canada
Posts: 8,978
|
added --no-fast-p-skip to RealAnime 4
Thanks for all the infos
__________________
Detritus Software |
8th January 2006, 21:14 | #9 | Link |
Registered User
Join Date: Mar 2005
Posts: 33
|
Sorry for offtop - don't wanna start new thread
I want to rip Star Wars III on 2 CD's - with upscaled to 1024x432 resolution and bitrate of 1240Kbit/s, how do you think is enough bitrate for such big resolution or i need to lower it to obtain better quality? Sorry for poor english |
8th January 2006, 23:01 | #10 | Link |
retired developer
Join Date: Oct 2002
Location: Canada
Posts: 8,978
|
Do you use --no-fast-p-skip? If no, you are out of topic
__________________
Detritus Software |
8th January 2006, 23:22 | #11 | Link |
Registered User
Join Date: Mar 2005
Location: Finland
Posts: 2,641
|
I think he is definitely on topic, if you only look at the topic
Anyway, that bitrate is probably fine for most people, but a higher bitrate (or a lower resolution) might improve quality a bit. This is something you just need to decide yourself: what is good enough for your eyes. Last edited by nm; 8th January 2006 at 23:24. |
9th January 2006, 14:02 | #12 | Link |
aka XaS
Join Date: Jun 2005
Location: France
Posts: 1,122
|
just a remark about treillis :
I tried several --crf 22 encodes with a couple of differing settings, and re-did them all with treillis 1 enabled ... the filesize of the treillis version of each encode was always bigger, but I couldn't see any quality improvement (well ok it was bicubicresized 512*384 anime so It was a bit blurry, but still...). Since someone said earlier that treillis allowed more compression of data I wanted to understand : why I could witness the opposite effect ? A non exhaustive list of the settings I used : CRF22, 6 bframes with bframe ratio = 1.6, RDO for Bframes and --subme 7, -minqp 20, --qcomp 0.7, CABAC enabled (obviously ), weighed biprediction, --bime, chromaQPoffset 4 ... the rest is pretty much the default settings. Just one question : - Should treillis be any more efficient in high/low motion scenes or does it simply not matter ? Just trying to understand the "wierd" figures I've observed recently
__________________
Q9300 OC @ 3.2ghz / Asus P5E3 / 4GB PC10600 / Geforce 8600 GTS |
9th January 2006, 21:42 | #13 | Link |
ekTOMBE STUDIOS
Join Date: Dec 2005
Location: Cuba
Posts: 254
|
THE SAME HAPPENS TO ME!!!
I always encode with fixed quantizer and trellis makes my files biggers. I have the same question: IS TRELLIS REALLY USEFUL? BTW:: using Xvid with a fixed quantizer and trellis, makes my files smallers.. a bug in x264??
__________________
So, it works or not??? |
|
|