FFmpeg for marking time video based on a reference date - ffmpeg

Question

I am trying to mark a timestamp in a video using drawtext filter.
FFmpeg easily marks timestamps based on localtime, gmtime or even PTS. However, I want to assign a reference time (start time) for the timestamp in order to represent the time the video was recorded (not encoded).
Reading the documentation, I found that option basetime can be used for this purpose. However it seems that is not working or I am missing something.
The command line I am using is:
ffmpeg -y -i input.mp4 -filter_complex drawtext="fontfile=/tmp/UbuntuMono-B.ttf: fontsize=36: fontcolor=yellow: box=1: boxcolor=black#0.4: text='Wall Clock Time\: %{gmtime\:%Y-%m-%d %T}': basetime=1456007118" output.mp4
By using basetime=1456007118, it was expected the start time was set to '02/20/2016 20:25:18' since 1456007118 is the UTC time for that time and date:
date -d '02/20/2016 20:25:18' +"%s" # format MM/DD/AAAA hh:mm:ss
1456007118
However, no error is issued by FFmpeg and the video is marked with current GMT, ignoring basetime option.
Any hint?
Thanks.
Complete information about FFmpeg version and output is:
ffmpeg -y -i /home/denio/Videos/Interstellar_2014_Trailer_4_5.1-1080p-HDTN.mp4 -filter_complex drawtext="fontfile=/tmp/UbuntuMono-B.ttf: fontsize=36: fontcolor=yellow: box=1: boxcolor=black#0.4: text='Wall Clock Time\: %{gmtime\:%Y-%m-%d %T}': basetime=1470226363" /tmp/x.mp4
ffmpeg version 3.1.1 Copyright (c) 2000-2016 the FFmpeg developers
built with gcc 5.3.1 (Ubuntu 5.3.1-14ubuntu2.1) 20160413
configuration: --enable-libxavs --enable-bzlib --enable-libfaac --enable-libfreetype --enable-libfontconfig --enable-libmp3lame --enable-libschroedinger --enable-libspeex --enable-libvorbis --enable-libx264 --enable-libx265 --enable-libxvid --enable-zlib --enable-x11grab --enable-static --enable-pthreads --enable-gpl --enable-nonfree --enable-version3 --disable-ffserver --enable-libgsm --enable-librtmp --enable-libvpx --enable-libschroedinger --enable-libopencore-amrnb --enable-libopenjpeg
libavutil 55. 28.100 / 55. 28.100
libavcodec 57. 48.101 / 57. 48.101
libavformat 57. 41.100 / 57. 41.100
libavdevice 57. 0.101 / 57. 0.101
libavfilter 6. 47.100 / 6. 47.100
libswscale 4. 1.100 / 4. 1.100
libswresample 2. 1.100 / 2. 1.100
libpostproc 54. 0.100 / 54. 0.100
...
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Answer 1

I see the basetime in the source code, but not in the web documentation, so not sure how it's supposed to work.
You can instead use the pts function.
ffmpeg -y -i input.mp4 -vf "drawtext=fontfile=/tmp/UbuntuMono-B.ttf:
fontsize=36:fontcolor=yellow:
box=1:boxcolor=black#0.4:
text='Wall Clock Time\: %{pts\:gmtime\:1456007118}'"
output.mp4
You may need to reset PTS (setpts=PTS-STARTPTS) before the drawtext.