[FFmpeg-user] 3D SBS with ffmpeg quality question

[Sully Beck]

On 05/24/2018 12:23 PM, Moritz Barsnick wrote:
> Hi Sully,
>
>> I am trying to come up with a reliable method to burn my 3D BluRays
>> to disk as
> Are you burning, as in "creating an optical disc", or are you ripping,
> as in "writing the BluRay disk's content to a file on harddisk"?

Ripping.  Ultimately, I want to write the contents of my 3D BluRays to 
3D SBS MP4 files on harddisk.

I apologize for using the wrong word.  I'm actually still early enough 
in the learning process, I know that I don't always use the correct terms.

> On Wed, May 23, 2018 at 22:07:06 -0400, Sully Beck wrote:
>> I'm not sure why you say that this cannot be correct.  I promise that
>> the above command is EXACTLY what I typed.
> Yes, but it is not exactly what the frame rate is. Have you even
> compared the output of your mediainfo commands?
>
> -Frame rate                               : 23.976 (24000/1001) FPS
> +Frame rate                               : 23.976 (23976/1000) FPS

I had compared those two lines.  I could see that the ratio was 
different, but I had assumed that they were 'close enough'. Probably 
another bad assumption on my part.  I'm sure I've made several of those 
in this process.  I will try again, again.


> The latter is from ffmpeg. You should have told ffmpeg to use
> "24000/1001", to be precise. It may or may not matter for your player
> though.
>
>> I do mean that the quality of the encoded file (ffmpeg) is inferior to
>> the PavTube version.
> Did you notice that you did "imitate" some of the details of the
> PavTube encoding, but not all? If, again, you compared your outputs,
> you would have noticed differences such as:
>   Format/Info                              : Advanced Video Codec
> -Format profile                           : Baseline at L4.1
> +Format profile                           : High at L4.1
>   Format settings, CABAC                   : No
> -Format settings, ReFrames                : 1 frame
> +Format settings, ReFrames                : 4 frames
>   Codec ID                                 : avc1

Like the framerate difference above, I saw those differences, but I 
wasn't sure that they would matter.  I probably need to just work to 
reproduce all of them.  I'll spend a bit more time and report back in a 
day or two.


> and especially:
>
> -Writing library                          : x264 core 148
> -Encoding settings                        : cabac=0 / ref=1 /
> -deblock=1:0:0 / analyse=0x1:0x111 / me=dia / subme=7 / psy=1 /
> -psy_rd=1.00:0.00 / mixed_ref=0 / me_range=4 / chroma_me=1 / trellis=0 /
> -8x8dct=0 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 /
> -threads=1 / lookahead_threads=1 / sliced_threads=0 / nr=0 / decimate=1 /
> -interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=0 /
> -weightp=0 / keyint=12 / keyint_min=7 / scenecut=40 / intra_refresh=0 /
> -rc_lookahead=12 / rc=abr / mbtree=1 / bitrate=15000 / ratetol=1.0 /
> -qcomp=0.60 / qpmin=3 / qpmax=51 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
> -Language                                 : English
> +Writing library                          : x264 core 152
> +Encoding settings                        : cabac=0 / ref=3 /
> +deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=7 / psy=1 /
> +psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 /
> +8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 /
> +threads=24 / lookahead_threads=4 / sliced_threads=0 / nr=0 / decimate=1
> +/ interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 /
> +b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 /
> +weightp=2 / keyint=250 / keyint_min=23 / scenecut=40 / intra_refresh=0 /
> +rc_lookahead=40 / rc=abr / mbtree=1 / bitrate=15000 / ratetol=1.0 /
> +qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
>
> Since PavTube uses libx264, you may have a chance of duplicating its
> results if you use those exact setting for x264. I don't know if you
> can hit them with an ffmpeg combination of "-preset" and bandwidth (and
> "-crf") options, or you have to duplicate them through the "x264opts"
> and "x264-params" options. But that's worth a try, unless someone
> figures out from looking at this why it yields worde results.
>
> I'm confused that ffmpeg's options seem to be trying harder to get a
> good quality/bandwidth ratio, but don't succeed according to your
> observation. But I'm no expert.
>
> Good luck,
> Moritz

Thanks for your reply.  I'll reply again once I've gotten closer.