When we use telnet and use launchprocess API, then only audio part comes from output file when we merge one video and one audio file.
You can refer same above in earlier post.
I have given 775 permission to media folder where output is being saved.
You can see attached screenshot of ubuntu terminal and please guide to me to resolve this issues as soon as problem.
If needed i can provide you server access to repeat it at your end.
Looking forward for you input.