The logic of the element requires the next buffer to be available
immediately after we are done pushing the previous, otherwise we insert
a repeat.
Making the src loop handle events and queries broke this, as upstream is
almost guaranteed not to deliver a buffer in time if we allow non-buffer
items to block upstream's push.
To fix this, replace our single-item `Option` with a `VecDeque` that we
allow to hold an unlimited number of events or queries, but only one
buffer at a time.
In addition, the code was confused about the current caps and segment.
This wasn't an issue before making the src loop handle events and
queries, as only the sinkpad cared about the current segment, using it
to buffers received, and only the srcpad cared about the current caps,
sending it just before sending the next received buffer.
Now the sinkpad cares about caps (through `update_fallback_duration`)
and the srcpad cares about the segment (when not in single-segment
mode).
Fix this by
- making `in_caps` always hold the current caps of the sinkpad,
- adding `pending_caps`, which is used by the srcpad to store
caps to be sent with the next received buffer,
- adding `in_segment`, holding the current segment of the sinkpad,
- adding `pending_segment`, which is used by the srcpad to store
the segment to be sent with the next received buffer,
- adding `out_segment`, holding the current segment of the srcpad.
Maybe a fix for
https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/issues/298.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1082>
It attempts to produce a (nearly) gapless live stream by synchronizing
its output to the running time and forwarding the next input buffer if
its start is (nearly) flush with the end of the last output buffer.
If the input buffer is missing or too far in the future, it duplicates
the last output buffer with adjusted timestamps. If it is operating on a
raw audio stream, it will fill duplicate buffers with silence.
If an input buffer arrives too late, it is thrown away. If the last
input buffer was accepted too long ago (according to `late-threshold`),
a late input buffer is accepted anyway, but immediately considered a
duplicate. Due to the silence-filling, this has no effect on audio, but
video gets a "slideshow" effect instead of freezing completely.
The "many-repeats" property will be notified when this element has
recently duplicated a lot of buffers or recovered from such a state.
Co-authored-by: Vivia Nikolaidou <vivia@ahiru.eu>
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/708>
