tl;dr: Update ffmpeg ± youtube-dl.
Including the console output was helpful!
Your inputs are only detected as 5 seconds long
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'https://r1---sn-j5cax8pnpvo-x1xe6.googlevideo.com/videoplayback?keepalive=yes&source=yt_live_broadcast&pl=24&itag=136&mime=video%2Fmp4&expire=1521354001&c=WEB&sparams=aitags%2Ccmbypass%2Cei%2Cgcr%2Cgir%2Chang%2Cid%2Cip%2Cipbits%2Citag%2Ckeepalive%2Clive%2Cmime%2Cmm%2Cmn%2Cms%2Cmv%2Cnoclen%2Cpl%2Crequiressl%2Csource%2Cexpire&aitags=133%2C134%2C135%2C136%2C160&signature=727E04BDE2851159A8A9327CDBAB503BBDC37267.2168845A24D2FFD5496AA2F5D2D6AACA59BB69D2&cmbypass=yes&ipbits=0&hang=1&beids=%5B9466592%5D&ms=lv&mt=1521331971&mv=u&live=1&key=yt6&ip=152.168.37.75&id=0R0T0mQmx7I.0&gir=yes&mm=32&mn=sn-j5cax8pnpvo-x1xe6&ei=sbCtWvOcLJTWxAS644e4Ag&noclen=1&gcr=ar&requiressl=yes&ratebypass=yes':
Metadata:
...
Duration: 00:00:05.00, start: 0.000000, bitrate: 2419 kb/s
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from 'https://r1---sn-j5cax8pnpvo-x1xe6.googlevideo.com/videoplayback?ip=152.168.37.75&mm=32&mn=sn-j5cax8pnpvo-x1xe6&expire=1521354004&pl=24&gir=yes&signature=16F13864FDF56FFDF2E08B248355CD1257D2E4FF.C7DBD2A865733005704660CD0EA82A90EFCFC03D&id=0R0T0mQmx7I.0&mt=1521331971&mv=u&ms=lv&hang=1&ipbits=0&itag=140&gcr=ar&requiressl=yes&source=yt_live_broadcast&keepalive=yes&ei=s7CtWsq0Ko7UxQT__pSgBA&noclen=1&sparams=cmbypass%2Ccompress%2Cei%2Cgcr%2Cgir%2Chang%2Cid%2Cip%2Cipbits%2Citag%2Ckeepalive%2Clive%2Cmime%2Cmm%2Cmn%2Cms%2Cmv%2Cnoclen%2Cpl%2Crequiressl%2Csource%2Cexpire&cmbypass=yes&compress=yes&key=yt6&mime=audio%2Fmp4&c=WEB&live=1&ratebypass=yes':
Metadata:
...
Duration: 00:00:04.99, start: 0.000000, bitrate: 130 kb/s
Your ffmpeg version is quite old
ffmpeg version 2.8.11-0ubuntu0.16.04.1 Copyright (c) 2000-2017 the FFmpeg developers
2.8 dates from around early 2016, from what I can tell. You are strongly suggested to update to the latest ffmpeg; preferably the latest git HEAD, but otherwise this PPA might be of use for Ubuntu.
Update your youtube-dl version as well
I get quite a different output from you for the same URL:
$ youtube-dl --list-formats https://www.youtube.com/watch?v=0R0T0mQmx7I
[youtube] 0R0T0mQmx7I: Downloading webpage
[youtube] 0R0T0mQmx7I: Downloading video info webpage
[youtube] 0R0T0mQmx7I: Extracting video information
[youtube] 0R0T0mQmx7I: Downloading m3u8 information
[youtube] 0R0T0mQmx7I: Downloading MPD manifest
[info] Available formats for 0R0T0mQmx7I:
format code extension resolution note
91 mp4 256x144 HLS 197k , avc1.42c00b, 30.0fps, mp4a.40.5@ 48k
92 mp4 426x240 HLS 338k , avc1.4d4015, 30.0fps, mp4a.40.5@ 48k
93 mp4 640x360 HLS 829k , avc1.4d401e, 30.0fps, mp4a.40.2@128k
94 mp4 854x480 HLS 1380k , avc1.4d401f, 30.0fps, mp4a.40.2@128k
95 mp4 1280x720 HLS 2593k , avc1.4d401f, 30.0fps, mp4a.40.2@256k (best)
$ youtube-dl --version
2018.03.14
With a recent ffmpeg and youtube-dl version, you get the expected result:
$ ffmpeg -i $(youtube-dl -f 91 -g https://www.youtube.com/watch?v=0R0T0mQmx7I) \
-i $(youtube-dl -f 95 -g https://www.youtube.com/watch?v=0R0T0mQmx7I) \
-c:v copy -c:a aac -strict experimental -t 00:02:00 output.mp4
(...)
$ ffprobe output.mp4
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf57.83.100
Duration: 00:02:00.02, start: 0.000000, bitrate: 1784 kb/s
Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt709), 1280x720 [SAR 1:1 DAR 16:9], 1648kb/s, 30 fps, 30 tbr, 90k tbn, 60 tbc (default)
Metadata:
handler_name : VideoHandler
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 129 kb/s (default)
Metadata:
handler_name : SoundHandler
Full output from ffmpeg invocation.
