send to mp4 (convert to mp4) using ffmpeg (src: https://superuser.com/a/440639). tested with mkv to mp4 and avi to mp4 conversions

win7-8-10-send-to-mp4.bat

@ECHO OFF
rem ***********************************************************************
rem * MOV to MPG batch converter. (2014-09-29 Sinx)                       *
rem *                                                                     *
rem * For installation just copy batch file to SendTo directory.          *
rem * On Win8 execute "SHELL:sendto" to go to Sendto folder.              *
rem *                                                                     *
rem * I got quite good compression rations with these parameters:         *
rem * vcodec=h264      codec used                                         *
rem * vb=10000         video bandwidth                                    *
rem * deinterlace=1    rebuild full pictures from keyframes and diffs.    *
rem * acodec=mp3       audio codec                                        *
rem * ab=128           128kbps mp3 quality                                *
rem * channels=2       stereo                                             *
rem *                                                                     *
rem * for parameters see                                                  *
rem * http://www.videolan.org/doc/vlc-user-guide/de/ch04.html             *
rem ***********************************************************************
echo **********************************************************************
echo MOV to MPG VLC batch converter called: %0 %1 %2 %3 %4 %5 %6 %7 %8
echo **********************************************************************
echo.
echo For installation, just copy batch file to SendTo folder..
echo.

SET _new_extention=mp4

:start
if "%~1"=="" (call goto :the_end)
CALL :SUB_CONVERT %1
SHIFT
goto :start


:SUB_CONVERT
SET _orig_path=%~1
rem SET _orig_extention=%_orig_filename:*.=%
echo %_orig_path%
SET _orig_extention=%_orig_path:*.=%
CALL SET _new_path=%%_orig_path%:.%_orig_extention%=.%_new_extention%%%
set _new_path="%_new_path%"
echo.
echo Converting %1 ======TO===== %_new_path% ...
echo.

rem if exist "%ProgramFiles%\VideoLAN\VLC\vlc.exe" (
rem SET _vlc_path="%ProgramFiles%\VideoLAN\VLC\vlc"
rem ) else (
rem SET _vlc_path="%ProgramFiles(x86)%\VideoLAN\VLC\vlc"
rem )

rem vlc implementation
rem SET _vlc_path="D:\Program Files\VideoLAN\VLC\vlc.exe"
rem CALL %_vlc_path% -I dummy -vvv %1 --sout=#transcode{vcodec=h264,vb=10000,deinterlace=1,acodec=mp3,ab=128,channels=2,samplerate=44100}:standard{access=file,mux=ts,dst=%_new_path%} vlc://quit

rem ffmpeg implementation
SET _ffmpeg_path="D:\Program Files\ffmpeg-20190105-2d580d7-win64-static\bin\ffmpeg.exe"

IF /I "%_orig_extention%"=="mkv" (
  CALL %_ffmpeg_path% -i %1 -c:v copy -c:a copy %_new_path%
  rem echo %_orig_extention% IS mkv
  rem pause
) ELSE (
  CALL %_ffmpeg_path% -i %1 %_new_path%
  rem echo %_orig_extention% is NOT mkv
  rem pause
)
GOTO :eof

:the_end
echo **********************************************************************
echo * FINISHED                                                           *
echo **********************************************************************
pause

right-click an mkv file... not tested with other video formats... could also fail if not a valid video.

also make sure that there's only one dot (.) in the file name so that the batch file can find the extension easily