[Updated! Aug 14 2020] YouTube recommended encoding settings on ffmpeg (+ libx264)

README.md

Parameters

Container: MP4

Parameter	YouTube recommends setting
-movflags faststart	moov atom at the front of the file (Fast Start)

Video codec: H.264

Parameter	YouTube recommends setting	Note
-c:v libx264	H.264
-profile:v high	High Profile
-bf 2	2 consecutive B frames
	Closed GOP	x264 produces closed gop as default
-g 30	GOP of half the frame rate.
	CABAC	Normally, x264 uses CABAC as an entropy encoder.
-crf 18	Variable bitrate.	Currently, YouTube does not have a bitrate limit. Refer official document: https://support.google.com/youtube/answer/1722171?hl=en
-pix_fmt yuv420p	Chroma subsampling: 4:2:0	If you like to encode HDR video, this comment might be helpful. https://gist.github.com/mikoim/27e4e0dc64e384adbcb91ff10a2d3678#gistcomment-2859601

Audio codec: AAC-LC

Parameter	YouTube recommends setting	Note
-c:a libfdk_aac -profile:a aac_low	AAC-LC	Fraunhofer FDK AAC is a high-quality codec library, but it does not compatible GPL. So your FFmpeg most likely does not contain it. Build FFmpeg manually or use a built-in AAC encoder instead of libfdk_aac.
-b:a 384k	Mono 128 kbps, Stereo 384 kbps, 5.1 512 kbps

Sample video

• https://youtu.be/UCTPyB0l37Y

References

• Recommended upload encoding settings - YouTube Help https://support.google.com/youtube/answer/1722171
• Encode/H.264 – FFmpeg https://trac.ffmpeg.org/wiki/Encode/H.264
• Encode/AAC – FFmpeg https://trac.ffmpeg.org/wiki/Encode/AAC
• x264 FFmpeg Options Guide - Linux Encoding https://sites.google.com/site/linuxencoding/x264-ffmpeg-mapping

encode.log

ffmpeg version N-98725-gcfc6552032 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 10 (GCC)
  configuration: --prefix=xxx --enable-nonfree --enable-gpl --enable-libfdk-aac --enable-libx264 --enable-libx265
  libavutil      56. 58.100 / 56. 58.100
  libavcodec     58.100.100 / 58.100.100
  libavformat    58. 50.100 / 58. 50.100
  libavdevice    58. 11.101 / 58. 11.101
  libavfilter     7. 87.100 /  7. 87.100
  libswscale      5.  8.100 /  5.  8.100
  libswresample   3.  8.100 /  3.  8.100
  libpostproc    55.  8.100 / 55.  8.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'source.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
  Duration: 00:00:23.60, start: 0.000000, bitrate: 13088 kb/s
    Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 3840x2160, 12970 kb/s, 23.98 fps, 23.98 tbr, 24k tbn, 47.95 tbc (default)
    Metadata:
      handler_name    : ?Mainconcept Video Media Handler
    Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 129 kb/s (default)
    Metadata:
      handler_name    : #Mainconcept MP4 Sound Media Handler
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
  Stream #0:1 -> #0:1 (aac (native) -> aac (libfdk_aac))
Press [q] to stop, [?] for help
[libx264 @ 0x2337f40] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2 AVX512
[libx264 @ 0x2337f40] profile High, level 5.1, 4:2:0, 8-bit
[libx264 @ 0x2337f40] 264 - core 159 r2999 296494a - H.264/MPEG-4 AVC codec - Copyleft 2003-2020 - 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=27 lookahead_threads=4 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=2 b_pyramid=2 b_adapt=1 b_bias=0 direct=3 weightb=1 open_gop=0 weightp=2 keyint=12 keyint_min=1 scenecut=40 intra_refresh=0 rc_lookahead=12 rc=crf mbtree=1 crf=18.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, mp4, to 'output.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.50.100
    Stream #0:0(eng): Video: h264 (libx264) (avc1 / 0x31637661), yuv420p, 3840x2160, q=-1--1, 23.98 fps, 24k tbn, 23.98 tbc (default)
    Metadata:
      handler_name    : ?Mainconcept Video Media Handler
      encoder         : Lavc58.100.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
    Stream #0:1(eng): Audio: aac (libfdk_aac) (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, s16, 384 kb/s (default)
    Metadata:
      handler_name    : #Mainconcept MP4 Sound Media Handler
      encoder         : Lavc58.100.100 libfdk_aac
[mp4 @ 0x2346280] Starting second pass: moving the moov atom to the beginning of the file0.881x    
frame=  565 fps= 20 q=-1.0 Lsize=   50496kB time=00:00:23.57 bitrate=17548.0kbits/s speed=0.828x    
video:49380kB audio:1107kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.017619%
[libx264 @ 0x2337f40] frame I:54    Avg QP:12.52  size:145222
[libx264 @ 0x2337f40] frame P:508   Avg QP:15.73  size: 83671
[libx264 @ 0x2337f40] frame B:3     Avg QP:15.72  size: 72715
[libx264 @ 0x2337f40] consecutive B-frames: 98.9%  1.1%  0.0%
[libx264 @ 0x2337f40] mb I  I16..4: 32.3% 61.1%  6.6%
[libx264 @ 0x2337f40] mb P  I16..4: 18.7% 32.0%  0.7%  P16..4: 21.4%  3.8%  1.2%  0.0%  0.0%    skip:22.1%
[libx264 @ 0x2337f40] mb B  I16..4:  4.4% 10.4%  0.4%  B16..8: 48.1%  7.4%  0.4%  direct: 3.5%  skip:25.4%  L0:65.6% L1:33.4% BI: 1.0%
[libx264 @ 0x2337f40] 8x8 transform intra:62.0% inter:85.3%
[libx264 @ 0x2337f40] direct mvs  spatial:33.3% temporal:66.7%
[libx264 @ 0x2337f40] coded y,uvDC,uvAC intra: 25.4% 34.5% 3.6% inter: 5.2% 15.3% 0.0%
[libx264 @ 0x2337f40] i16 v,h,dc,p: 11% 21%  8% 60%
[libx264 @ 0x2337f40] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 30% 18% 23%  4%  5%  5%  6%  5%  5%
[libx264 @ 0x2337f40] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 32% 16% 18%  5%  8%  7%  6%  4%  4%
[libx264 @ 0x2337f40] i8c dc,h,v,p: 56% 22% 17%  5%
[libx264 @ 0x2337f40] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 0x2337f40] ref P L0: 72.7%  1.1% 15.9%  6.0%  2.6%  1.7%
[libx264 @ 0x2337f40] ref B L0: 89.1%  7.4%  3.5%
[libx264 @ 0x2337f40] kb/s:17165.92

encode.sh

#!/bin/bash

AAC_ENCODER=libfdk_aac
# AAC_ENCODER=aac

AUDIO_PARAMS="-c:a $AAC_ENCODER -profile:a aac_low -b:a 384k"
VIDEO_PARAMS="-pix_fmt yuv420p -c:v libx264 -profile:v high -preset slow -crf 18 -g 30 -bf 2"
CONTAINER_PARAMS="-movflags faststart"

# You need to adjust the GOP length to fit your source video.
# 60 fps -> -g 30
# 23.976 (24000/1001) -> -g 24000/1001/2  (???) <- plz comment

ffmpeg -i "$1" $AUDIO_PARAMS $VIDEO_PARAMS $CONTAINER_PARAMS "$2"

mediainfo-output-mp4.log

General
Complete name                            : output.mp4
Format                                   : MPEG-4
Format profile                           : Base Media
Codec ID                                 : isom (isom/iso2/avc1/mp41)
File size                                : 49.3 MiB
Duration                                 : 23 s 616 ms
Overall bit rate                         : 17.5 Mb/s
Writing application                      : Lavf58.50.100

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : [email protected]
Format settings                          : CABAC / 5 Ref Frames
Format settings, CABAC                   : Yes
Format settings, Reference frames        : 5 frames
Format settings, GOP                     : M=1, N=11
Codec ID                                 : avc1
Codec ID/Info                            : Advanced Video Coding
Duration                                 : 23 s 566 ms
Bit rate                                 : 17.2 Mb/s
Width                                    : 3 840 pixels
Height                                   : 2 160 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 23.976 (24000/1001) FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.086
Stream size                              : 48.2 MiB (98%)
Writing library                          : x264 core 159 r2999 296494a
Encoding settings                        : 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=27 / lookahead_threads=4 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=2 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=3 / weightb=1 / open_gop=0 / weightp=2 / keyint=12 / keyint_min=1 / scenecut=40 / intra_refresh=0 / rc_lookahead=12 / rc=crf / mbtree=1 / crf=18.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
Language                                 : English
Codec configuration box                  : avcC

Audio
ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 23 s 616 ms
Bit rate mode                            : Constant
Bit rate                                 : 384 kb/s
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 SPF)
Compression mode                         : Lossy
Stream size                              : 1.08 MiB (2%)
Language                                 : English
Default                                  : Yes
Alternate group                          : 1

@eladkarako

prevent pyramidal B-frames with -bf_ref 0.

Do things like this matter if the intention is to upload these video to YouTube? YouTube will re-encode all videos uploaded to it so if that's the use case I don't think there's much point in tweaking encoding params to improve player compatibility. (I've even used YouTube as a free video transcoding service by uploading a buggy video, then downloading YouTube's fixed version of it). If the intention is to upload to YouTube, and you don't mind uploading a lot, I'd just encoded with -preset superfast -crf 15, or even lossless -crf 0, and trust YouTube will re-encode my video 20 different ways for player compatibility.

That said if I'm serving my encoded .mp4 directly to users, this is valuable info! Had no idea about pyramidal b-frames

@varenc for long duration video, when upload it to studio, it got so much time to finish upload,processing and finally copyright check process.
I just want to know