Couldn't determine type of stream

[myaspm]

Hello, i was trying to merge two videos and sink it to a file. This pipe
creates a file but cant play it in Ubuntu, it gives the error "Couldn't
determine type of stream"

My pipeline is : 

/"gst-launch-1.0 compositor name=mixer sink_1::alpha=0.5 sink_1::xpos=50
sink_1::ypos=50 !  queue2 ! filesink location=out1.mp4 filesrc
location=1.mp4 ! decodebin name=db ! videoscale ! videoconvert ! queue2 !
mixer. filesrc location=2.mp4 ! decodebin ! videoscale ! videoconvert !
queue2  ! mixer. db. ! audioconvert ! audioresample ! voaacenc"/

I believe i need to encode (or mux?) the videos somehow but couldn't get it
to work. What i need to do?

Thanks in advance.



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