95ff949eff
And use the output segment position for the outgoing timestamp while it is. This is needed to delay the calculation of `output_ts_offset` until we actually have a usable timestamp, as tsmux will output a few initial packets while `last_ts` is still unset. Without this, the calculation would use the initial `0` value, which did not have the intended effect of making VBR mode behave like CBR mode, but always calculated an offset equal to the selected start time. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1884>