Are CRF values consistent accross different resolutions

[R3Z]

I have been using crf 19 for my 720x576 encodes and with my particular settings i have been getting at least 40% compression over the original mpeg 2 file.

Since i have started recording in 720p, i thought logically encoding with x264 should give a similar gain, but thats not the case. The filesize is always 5-10% more than the original (wtf).

These 720p videos have been scaled by the broadcaster from 576p, so i kinda dont get why compression is suffering.

My question is that, do crf values remain consistent accross resolutions ? I am having issues working out just why there is no compression gain here.

My settings are btw;

x264.exe --sar 407:395 --deadzone-inter 10 --deadzone-intra 5 --crf 19 --ref 8 --mixed-refs --no-fast-pskip --bframes 4 --b-pyramid --b-rdo --bime -8 --weightb --direct auto --filter -2,-1 --subme 6 --analyse all --8x8dct --me umh --threads auto --thread-input --cqmfile "prestige.cfg" --progress --no-dct-decimate --output "kaiser.mp4" "kaiser.avs"

pause

[Dark Shikari]

It could be that the original HD MPEG-2 bitrate-per-pixel is lower than that of the SD file.

[check]

CRF is basically a space efficient version of constant quantizer (--qp). As such, because it is based on quantizers, the quality is mathematically independant of resolution. That said, most find that the higher the resolution, the greater the perceptual quality for a given ratefactor. In other words, you can use a higher crf value (try 20-23) for the same relative quality as with a lower resolution.

btw, there's not much point encoding 576p as 720p :) If you want to see the total lack of usefulness, compare the output of these two avisynth scripts:
source("upscaled-576p.ts")
source("upscaled-576p.ts").spline36resize(720,576).spline36resize(1280,720)

[R3Z]

CRF is basically a space efficient version of constant quantizer (--qp). As such, because it is based on quantizers, the quality is mathematically independant of resolution. That said, most find that the higher the resolution, the greater the perceptual quality for a given ratefactor. In other words, you can use a lower crf value (try 20-23) for the same relative quality as with a lower resolution.

btw, there's not much point encoding 576p as 720p :) If you want to see the total lack of usefulness, compare the output of these two avisynth scripts:
source("upscaled-576p.ts")
source("upscaled-576p.ts").spline36resize(720,576).spline36resize(1280,720)

Ahh ! Good call :) The upscaling was already done on their end, so it makes sense to compare an sd clip with their upscaled stuff (they are just music videos after all).

This just really threw me off guard. Travelling nicelly, then bang i hit a wall !

[R3Z]

Just to close this one off, it appears as if the dvico software was lying when it said the bitrate being recorded was 15mbps. The actual bitrate was 9.6mbps for 720p which is way too low hence all these issues.

[Manao]

In other words, you can use a lower crf value (try 20-23) for the same relative quality as with a lower resolution.You meant higher ?

Apart from that, CRF isn't totally independant of the resolution, since higher resolutions at a given quantizer give a relatively lower filesize ( in addition to being visually more pleasing ).

The bigger the resolution, the less detail/macroblock, so it makes sense. Furthermore, for intra frame especially, the bigger the resolution the more efficient the encoding process ( though that effect is small in comparison to the detail/macroblock one ).

[PuzZLeR]

CRF is directly related to rez and fps. You will get different file sizes for the same quantizer with different resolutions and frame rates, regardless of where the source is from ... at least in theory.

The higher the rez, the higher the final file size for the same quantizer - more screen size to contribute the same quality to, hence more bitrate needed.

The higher the fps, the higher the final file size for the same quantizer again - more frames to contribute the same quality to, hence more bitrate needed.

they are just music videos after allShame on you! :eek: I'm hurt. :mad: Music videos are sacred! :p I have a collection of over 5000 of them which is my biggest reason for video compression. Too awkward for DvD authoring, they're better off like an MP3 collection... real cool!:p

[audyovydeo]

Music videos are sacred! :p I have a collection of over 5000 of them

mmmmhhh... I wonder if you'll allow me to make a request for a long-lost 1980s video clip which I loved. By MP if you prefer ?

audyovydeo

[PuzZLeR]

I wonder if you'll allow me to make a request for a long-lost 1980s video clip which I loved.

Hey A/V,

By all means. Although I have a specific taste, if I have it, I'd be more than glad to upload it for you.:) Since I've strayed from topic already, hit me with the request in my PM box. I'll let you know.

[R3Z]

Shame on you! :eek: I'm hurt. :mad: Music videos are sacred! :p I have a collection of over 5000 of them which is my biggest reason for video compression. Too awkward for DvD authoring, they're better off like an MP3 collection... real cool!:p

Dont get me wrong mate :) Music videos are the only reason i have videos on my HTPC :) The broadcaster here (abc) has a program called rage which runs fridays and saturday nights and goes for 10 hours of non stop music videos. There is only one small rage logo which is easily cut out too!

I will get a list together soon and let you know what i have got.

[PuzZLeR]

Dont get me wrong mate :) Music videos are the only reason i have videos on my HTPC :)No big deal my friend. It was just a bit of humor on my part anyway, even if you did dislike music videos. There are even some people who will argue that they kill "music" in general because the music video takes you away from the "music" entirely. I do believe this somewhat too, but since I've started collecting these things since VHS, it's become a habit I guess. Then again they're lots of fun anyway!

About the station's logo, it's usually a watermark. Yeah, with my editing software, and some "surgery", I can remove it, or mask it with an overlay, but it's not a big deal really.

Just curious what you do in this case, or you can PM me if you like no problem.