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player,bench: drop queue from vscale-bin (leaky=2 caused massive drops), keep nearest-neighbour

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This commit is contained in:
Matteo Benedetto
2026-03-24 10:54:02 +01:00
parent 65665f4cff
commit 995830e3d2
2 changed files with 25 additions and 42 deletions
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src/r36s_dlna_browser/player/gstreamer_backend.py
+17 -28
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@@ -428,42 +428,33 @@ class GStreamerBackend(PlayerBackend):
sink.set_property("caps", self._gst.Caps.from_string("video/x-raw,format=BGRA"))
return sink
# Hardware decode (NV12): insert a queue → videoscale → capsfilter chain
# inside a GstBin before the appsink so playbin accepts it as a single
# video-sink element.
# Hardware decode (NV12): insert a videoscale → capsfilter chain inside a
# GstBin before the appsink so playbin accepts it as a single video-sink.
#
# queue — decouples mppvideodec from the scale thread so the HW
# decoder is never stalled waiting for SW scaling to finish.
# leaky=2 (downstream) drops the oldest queued frame when
# full, ensuring Python always receives the latest frame.
# videoscale(method=nearest-neighbour) — scales 1920×1080 → 640×480.
# Nearest-neighbour skips ~56% of source rows so only ~44% of the
# source cache lines are fetched. This is cheaper than the full
# 3.1 MB memmove (which loads 100% of cache lines), cutting the
# Python memmove from ~32 ms to ~1 ms at the cost of some SW scale
# CPU time (~14 ms estimated for nearest vs 32 ms for bilinear).
#
# videoscale(method=nearest) — scales 1920×1080 → 640×480 using
# nearest-neighbour interpolation (fastest SW method).
# Python receives 460 KB per frame instead of 3.1 MB,
# cutting memmove cost from ~32 ms to ~1 ms (30× reduction).
#
# capsfilter — enforces the target resolution and NV12 format so
# GStreamer's autoplugging can insert any needed conversion.
# capsfilter — enforces the output NV12 dimensions.
app_w, app_h = self._viewport[0], self._viewport[1]
scale_w, scale_h = (app_w or 640), (app_h or 480)
log.info("NV12 appsink: queue → videoscale(nearest) → %dx%d before appsink", scale_w, scale_h)
log.info("NV12 appsink: videoscale(nearest) → %dx%d before appsink", scale_w, scale_h)
queue = self._gst.ElementFactory.make("queue", "vqueue")
scale = self._gst.ElementFactory.make("videoscale", "vscale")
capsfilter = self._gst.ElementFactory.make("capsfilter", "vcaps")
if queue is None or scale is None or capsfilter is None:
if scale is None or capsfilter is None:
# Core elements unavailable — fall back to unscaled NV12.
log.warning("queue/videoscale/capsfilter unavailable; using unscaled NV12 appsink")
log.warning("videoscale/capsfilter unavailable; using unscaled NV12 appsink")
sink.set_property("caps", self._gst.Caps.from_string(
"video/x-raw,format=NV12;video/x-raw,format=BGRA"))
return sink
# nearest-neighbour: reads only the needed source pixels (strided),
# much cheaper than bilinear which reads all adjacent pixels.
# nearest-neighbour: accesses only the source pixels needed for each
# output sample (strided reads), skipping ~56% of source rows entirely.
scale.set_property("method", 0)
# drop oldest buffered frame when queue is full — keep the latest.
queue.set_property("max-size-buffers", 4)
queue.set_property("leaky", 2)
capsfilter.set_property(
"caps",
self._gst.Caps.from_string(
@@ -471,19 +462,17 @@ class GStreamerBackend(PlayerBackend):
),
)
# Wire queue → scale → capsfilter → appsink inside a bin.
# Wire scale → capsfilter → appsink inside a bin.
bin_ = self._gst.Bin.new("vscale-bin")
bin_.add(queue)
bin_.add(scale)
bin_.add(capsfilter)
bin_.add(sink)
queue.link(scale)
scale.link(capsfilter)
capsfilter.link(sink)
# Expose the queue element's sink pad as the bin's ghost sink pad
# Expose the scale element's sink pad as the bin's ghost sink pad
# so playbin can push decoded frames into the bin.
sink_pad = queue.get_static_pad("sink")
sink_pad = scale.get_static_pad("sink")
ghost = self._gst.GhostPad.new("sink", sink_pad)
ghost.set_active(True)
bin_.add_pad(ghost)