Copied from https://gitlab.freedesktop.org//gstreamer/gst-plugins-good/-/merge_requests/395
When we start with a video frame with a presentation offset, this ensures our initial frames (video or audio) don't fall outside the segment and get clipped later.
A simple remuxer now keeps the right timestamps:
gst-launch-1.0 \
filesrc location=$HOME/foo.flv ! flvdemux name=d \
d. ! queue ! h264parse ! m. \
d. ! queue ! aacparse ! m. \
flvmux streamable=1 name=m ! filesink location=$HOME/bar.flv