I wonder why decodebin can directly connect to autovideosink, but it can NOT directly connect to autoaudiosink!
$ gst-launch-1.0 filesrc location=myfile.mp4 ! decodebin ! autoaudiosink [not OK]
$ gst-launch-1.0 filesrc location=myfile.mp4 ! decodebin ! autovideosink [OK]
I tested your pipeline and it worked on my side, which error are you seeing? Maybe you can add more debug to the command, for example:
GST_DEBUG=2 gst-launch-1.0 filesrc location=myfile.mp4 ! decodebin ! autoaudiosink -v
Could you try this one?
gst-launch-1.0 filesrc location=myfile.mp4 ! qtdemux ! avdec_aac ! autoaudiosink
You could also try adding an audioconvert before the sink
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