How to get FFMPEG output the same quality as Vimeo?
ffmpeg example
tl;dr: The important options are -preset slow and -crf 20:
ffmpeg -i input -c:v libx264 -preset slow -crf 20 -vf format=yuv420p -c:a aac -ac 2 -movflags +faststart output.mp4

The other options are to ensure compatibility.

How to find out what Vimeo uses
1. Download video using youtube-dl:
youtube-dl https://vimeo.com/123456789

2. Get encoding info
Assuming x264 is used to encode, and the encoding settings weren't stripped out, you can see what version was used and view the encoding settings.
Using mediainfo
Refer to the &quot;Encoding settings&quot; line.
mediainfo input.mp4

Using strings (Linux or macOS)
strings input.mp4 | grep x264

Example output
x264 - core 157 r10 d4099dd - H.264/MPEG-4 AVC codec - Copyleft 2003-2019 - http://www.videolan.org/x264.html - options: cabac=1 ref=5 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=8 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=2 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=34 lookahead_threads=5 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 stitchable=1 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=2 b_bias=0 direct=3 weightb=1 open_gop=0 weightp=2 keyint=infinite keyint_min=23 scenecut=40 intra_refresh=0 rc_lookahead=50 rc=crf mbtree=1 crf=20.0 qcomp=0.60 qpmin=5 qpmax=69 qpstep=4 vbv_maxrate=5500 vbv_bufsize=15000 crf_max=0.0 nal_hrd=none filler=0 ip_ratio=1.40 aq=1:1.00

This shows that -preset slow and -crf 20 were used. The options are set by -preset, so there is no need to manually attempt to set each option.

VBV is enabled for streaming. In ffmpeg this is set with -maxrate 5500k and -bufsize 15000k. I just used the values shown in the encoding settings above.

Thanks to Vimeo for not stripping the SEI (they certainly could have like YouTube) and allowing us to see what they used. Perhaps they wanted to show that they appreciate the open source tools they use.


Also see

FFmpeg Wiki: H.264 Video Encoding Guide
FFmpeg Wiki: AAC Audio Encoding Guide