When converting mkv to mp4, the audio is lost
ubuntu-14.04,mp4,video-encoding,mkv
In an MP4 container, browsers usually support only H.264 video and either AAC or MP3 audio. The output from your avconv command should show the format of your video and audio; look under "Input #0" for the lines that start with "Stream #". If you audio is not already AAC...
mkvmerge linux command Backward Spliting not supported
I just have a look at the manual: https://www.bunkus.org/videotools/mkvtoolnix/doc/mkvmerge.html#mkvmerge.description.split I saw but can't work it. Not displaying details about these. So, if backward splitting not support then you can first cut into pieces from original & then join with backward & upward portion one by one....