Is AutoMKV's lossless encoding really lossless?

[Chengbin]

I'm wondering if AutoMKV's lossless encoding is really lossless. I used the constant quality profile with unlimited size and the output file is a lot smaller than the original (1/5). Is there any video comparison software I can use to check if it is trully lossless?

BTW I'm using AutoMKV 0.96 beta 19. The movie is Cars, I clipped 19 minutes of video (3GB, H.264) and I encoded in lossless with AutoMKV and the output file was only 622MB

[Sharktooth]

CRF and QP 0 are lossless in x264. i dont know about automkv, but it uses x264 that has indeed a lossless mode. however, i have doubts the lossless encode will be smaller than the original unless your source was uncompressed...
use avisynth to compare the source and the encoded file. a PSNR of 50 means it's lossless.

[Chengbin]

The source is Bluray, it's not uncompressed, but the bitrate is about 30MB/sec

I have Avisynth 2.5, but how do I use it? I don't even see a .exe file.

BTW, the source file is .ts and the encoded lossless file is .mkv

[buzzqw]

automkv don't have a lossless profile.
I used the constant quality profile with unlimited size and the output file is a lot smaller than the original (1/5).

BUT what quantitizer have you select ? that's the question!

even if you select Unlimited file size, the profile is bound to minimun quantitizer in profile (10). Check it.

BHH

[Chengbin]

I chose 18 (which is default), I don't know what quantitizer is, so I just chose the default 18. What should I choose?

[buzzqw]

CRF and QP 0 is lossless in h.264. i dont know about automkv, but it uses x264 that has indeed a lossless mode. however, i have doubts the lossless encode will be smaller than the original unless your source was uncompressed...

That's the answer. But i suggest to try "All Profile" and select Lossless profile

BHH

[Dark Shikari]

Only a quantizer of 0 is lossless.

[Chengbin]

Is the lossless profile in AutoMKV predictive encoding?

[Dark Shikari]

Is the lossless profile in AutoMKV predictive encoding?No, x264 doesn't support High Predictive Profile, mainly because no decoder exists (as far as I know) that supports it correctly: not even JM does (it has at least two errors in its support, rendering it useless).

I have patches for both x264 and ffmpeg that add High Predictive support, but I'm waiting on CoreAVC and DivX to add support as they have promised.

[Chengbin]

You're right, the lossless version produced twice the file size as the original. If I encode the movie Cars to 8GB with AC3 audio from the original source, about how much loss of quality do you expect?

[Sharktooth]

it cant be said. it all depends on the movie compressibility. that said a CRF 18 encode will look almost "transparent" to most ppl. if you consider CRF 18 as 100% quality you can do some maths and compare the 8gb encode bitrate (subtract the audio bitrate from the calculations) to the CRF 18 encode bitrate. the difference is how much quality are you loosing...

[Chengbin]

Can you explain "transparent". When I encoded Cars in CRF 18, It looked pretty lossless (even with huge zooms) to me until people told me that it's not.

[buzzqw]

the keyword is AQ

automkv (and megui) use latest implementation of x264 so the AQ is always ON. This bring a very good quality images even on difficult spot.
Previus version of codec don't have/use it, so .. even at crf 18.. quality doesn't look so good

BHH

[J_Darnley]

Chengbin, transparent refers to the point at which you cannot tell the difference between the source and the encoded copy. This is not lossless because as that word suggests, there is absolutely no information/detail lost.