I asked InMotion to look into this further, and this was their reply:
Hello Vince,
Thank you for contacting us.
The issues encountered appear to be related to the site software as when the command provided in the error is run directly from the command line the operation completes without issue.
root@vps15082 [~]# /usr/local/bin/ffmpeg -y -i /home/quinnguitar/public_html/images/video/originalvideos/705/gn1Ut2myneh.mp4 -vcodec libx264 -acodec aac -ab 64k -strict -2 -crf 23 -vf "scale=640:-2" /home/quinnguitar/public_html/images/video/videos/705/LpbslJad3Qn.mp4
ffmpeg version N-91046-g974eb4a Copyright (c) 2000-2018 the FFmpeg developers
built with gcc 4.4.7 (GCC) 20120313 (Red Hat 4.4.7-18)
configuration: --enable-gpl --enable-shared --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libass --extra-libs=-lpthread --enable-openssl --libdir=/usr/lib64 --pkg-config-flags=--static --enable-nonfree
libavutil 56. 18.102 / 56. 18.102
libavcodec 58. 19.101 / 58. 19.101
libavformat 58. 13.102 / 58. 13.102
libavdevice 58. 4.100 / 58. 4.100
libavfilter 7. 22.100 / 7. 22.100
libswscale 5. 2.100 / 5. 2.100
libswresample 3. 2.100 / 3. 2.100
libpostproc 55. 2.100 / 55. 2.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/home/quinnguitar/public_html/images/video/originalvideos/705/gn1Ut2myneh.mp4':
Metadata:
major_brand : mp42
minor_version : 1
compatible_brands: mp42avc1
creation_time : 2016-12-11T06:47:34.000000Z
Duration: 00:01:00.53, start: 0.000000, bitrate: 3503 kb/s
Stream #0:0(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 129 kb/s (default)
Metadata:
creation_time : 2016-12-11T06:47:34.000000Z
handler_name : Apple Sound Media Handler
Stream #0:1(eng): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt709), 1398x1048, 1596 kb/s, 29.97 fps, 29.97 tbr, 2997 tbn, 5994 tbc (default)
Metadata:
creation_time : 2016-12-11T06:47:34.000000Z
handler_name : Apple Video Media Handler
Stream #0:2(eng): Data: none (rtp / 0x20707472), 1636 kb/s
Metadata:
creation_time : 2016-12-11T06:47:34.000000Z
handler_name : hint media handler
Stream #0:3(eng): Data: none (rtp / 0x20707472), 133 kb/s
Metadata:
creation_time : 2016-12-11T06:47:34.000000Z
handler_name : hint media handler
Stream mapping:
Stream #0:1 -> #0:0 (h264 (native) -> h264 (libx264))
Stream #0:0 -> #0:1 (aac (native) -> aac (native))
Press [q] to stop, [?] for help
[libx264 @ 0x179c0c0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2
[libx264 @ 0x179c0c0] profile High, level 3.0
[libx264 @ 0x179c0c0] 264 - core 155 - H.264/MPEG-4 AVC codec - Copyleft 2003-2018 - http://www.videolan.org/x264.html - options: cabac=1 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=15 lookahead_threads=2 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=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, mp4, to '/home/quinnguitar/public_html/images/video/videos/705/LpbslJad3Qn.mp4':
Metadata:
major_brand : mp42
minor_version : 1
compatible_brands: mp42avc1
encoder : Lavf58.13.102
Stream #0:0(eng): Video: h264 (libx264) (avc1 / 0x31637661), yuv420p, 640x480, q=-1--1, 29.97 fps, 11988 tbn, 29.97 tbc (default)
Metadata:
creation_time : 2016-12-11T06:47:34.000000Z
handler_name : Apple Video Media Handler
encoder : Lavc58.19.101 libx264
Side data:
cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 64 kb/s (default)
Metadata:
creation_time : 2016-12-11T06:47:34.000000Z
handler_name : Apple Sound Media Handler
encoder : Lavc58.19.101 aac
frame= 1814 fps=125 q=-1.0 Lsize= 8784kB time=00:01:00.53 bitrate=1188.7kbits/s speed=4.18x
video:8242kB audio:476kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.750084%
[libx264 @ 0x179c0c0] frame I:13 Avg QP:21.54 size: 12788
[libx264 @ 0x179c0c0] frame P:468 Avg QP:23.22 size: 7942
[libx264 @ 0x179c0c0] frame B:1333 Avg QP:25.52 size: 3418
[libx264 @ 0x179c0c0] consecutive B-frames: 1.5% 1.0% 1.8% 95.7%
[libx264 @ 0x179c0c0] mb I I16..4: 26.7% 55.0% 18.2%
[libx264 @ 0x179c0c0] mb P I16..4: 18.6% 29.1% 5.8% P16..4: 17.9% 6.8% 3.1% 0.0% 0.0% skip:18.7%
[libx264 @ 0x179c0c0] mb B I16..4: 1.3% 2.0% 0.7% B16..8: 24.1% 8.9% 2.5% direct:23.5% skip:37.1% L0:47.6% L1:48.2% BI: 4.2%
[libx264 @ 0x179c0c0] 8x8 transform intra:53.9% inter:70.0%
[libx264 @ 0x179c0c0] coded y,uvDC,uvAC intra: 34.9% 80.1% 60.8% inter: 10.8% 38.3% 9.0%
[libx264 @ 0x179c0c0] i16 v,h,dc,p: 49% 45% 3% 3%
[libx264 @ 0x179c0c0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 22% 38% 19% 3% 4% 3% 5% 2% 5%
[libx264 @ 0x179c0c0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 24% 43% 14% 2% 4% 3% 5% 2% 3%
[libx264 @ 0x179c0c0] i8c dc,h,v,p: 45% 40% 6% 9%
[libx264 @ 0x179c0c0] Weighted P-Frames: Y:1.1% UV:0.6%
[libx264 @ 0x179c0c0] ref P L0: 66.2% 9.6% 16.4% 7.8% 0.0%
[libx264 @ 0x179c0c0] ref B L0: 91.6% 6.7% 1.6%
[libx264 @ 0x179c0c0] ref B L1: 97.1% 2.9%
[libx264 @ 0x179c0c0] kb/s:1115.43
[aac @ 0x179a1c0] Qavg: 145.937
So, this appears to rule out any PHP settings as you mentioned. The server is able to do the conversion, just not through the cron link to JomSocial. Please look into this further, as this function is the sole reason we installed JomSocial in the first place.