The magic youtube-dl incantation to prefer high frame-rate content and mux the separate audio and video into a single file.

ytdl-hfr-mux.txt

# list the available formats for a youtube URL.
bash-3.2$ youtube-dl -F 'https://www.youtube.com/watch?v=NlFU2wM-f8g'
[youtube] NlFU2wM-f8g: Downloading webpage
[youtube] NlFU2wM-f8g: Extracting video information
[youtube] NlFU2wM-f8g: Downloading DASH manifest
[info] Available formats for NlFU2wM-f8g:
format code extension resolution  note 
140         m4a       audio only  DASH audio  129k , m4a_dash container, aac  @128k (44100Hz), 5.35MiB (worst)
141         m4a       audio only  DASH audio  255k , m4a_dash container, aac  @256k (44100Hz), 10.62MiB
160         mp4       230x144     DASH video  112k , 15fps, video only, 4.34MiB
133         mp4       384x240     DASH video  275k , 30fps, video only, 10.22MiB
134         mp4       576x360     DASH video  348k , 30fps, video only, 7.92MiB
135         mp4       768x480     DASH video  701k , 30fps, video only, 16.99MiB
136         mp4       1152x720    DASH video 1437k , 30fps, video only, 36.61MiB
298         mp4       1152x720    DASH video 2142k , h264, 60fps, video only, 49.32MiB
137         mp4       1728x1080   DASH video 2859k , 30fps, video only, 76.88MiB
299         mp4       1728x1080   DASH video 4612k , h264, 60fps, video only, 104.16MiB
264         mp4       1920x1440   DASH video 5790k , 30fps, video only, 139.80MiB
17          3gp       176x144     
36          3gp       320x240     
5           flv       400x240     
43          webm      640x360     
18          mp4       640x360     
22          mp4       1280x720    (best)

# Prefer 1080 HFR (high frame rate) video + bestaudio, then 720 HFR video + best audio, 
and then fall back to the default, which is the one Youtube tags 'best', which is 
usually the best *muxed* file and is very commonly 1280x720 mp4. DASH stores audio and 
video in separate files, however iOS isn't quite ready for that yet, so we ask youtube-dl 
to mux the audio and video into one output file (using the "v_format+a_format" args to 
the -f option below). The reason I don't just say bestvideo+bestaudio is because bestvideo 
would be 1440p30, and I'd much rather have 1080p60.

bash-3.2$ youtube-dl -f 299+bestaudio/298+bestaudio 'https://www.youtube.com/watch?v=NlFU2wM-f8g'
[youtube] NlFU2wM-f8g: Downloading webpage
[youtube] NlFU2wM-f8g: Extracting video information
[youtube] NlFU2wM-f8g: Downloading DASH manifest
[download] Destination: Bandicam Banana Phone and discrete audio tracks-NlFU2wM-f8g.f299.mp4
[download] 100% of 104.16MiB in 00:17
[download] Destination: Bandicam Banana Phone and discrete audio tracks-NlFU2wM-f8g.f141.m4a
[download] 100% of 10.62MiB in 00:01
[ffmpeg] Merging formats into "Bandicam Banana Phone and discrete audio tracks-NlFU2wM-f8g.mp4"

# Look at the streams in the output file. There are two streams!
bash-3.2$ ffprobe "Bandicam Banana Phone and discrete audio tracks-NlFU2wM-f8g.mp4" 2>&1 | grep Stream
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1728x1080 [SAR 1:1 DAR 8:5], 2497 kb/s, 60 fps, 60 tbr, 90k tbn, 120 tbc (default)
    Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 253 kb/s (default)