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player,bench: add queue+nearest-neighbour before videoscale to prevent pipeline stalls

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This commit is contained in:
Matteo Benedetto
2026-03-24 10:49:14 +01:00
parent 435bd51bbe
commit 65665f4cff
2 changed files with 49 additions and 19 deletions
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src/r36s_dlna_browser/player/gstreamer_backend.py
+35 -15
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@@ -428,24 +428,42 @@ class GStreamerBackend(PlayerBackend):
sink.set_property("caps", self._gst.Caps.from_string("video/x-raw,format=BGRA"))
return sink
# Hardware decode (NV12): insert a videoscale element before the appsink
# so mppvideodec can decode at full resolution in HW, but Python only
# receives a frame scaled to the display size (default 640x480).
# This cuts the memmove from 3.1 MB (1080p) to ~460 KB (640x480) per frame
# — a 6.7× reduction in CPU copy cost.
# 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.
#
# 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) — 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.
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: inserting videoscale → %dx%d before appsink", scale_w, scale_h)
log.info("NV12 appsink: queue → videoscale(nearest) → %dx%d before appsink", scale_w, scale_h)
scale = self._gst.ElementFactory.make("videoscale", "vscale")
capsfilter = self._gst.ElementFactory.make("capsfilter", "vcaps")
if scale is None or capsfilter is None:
# videoscale not available — fall back to unscaled NV12
log.warning("videoscale element unavailable; using unscaled NV12 appsink")
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:
# Core elements unavailable — fall back to unscaled NV12.
log.warning("queue/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.
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(
@@ -453,17 +471,19 @@ class GStreamerBackend(PlayerBackend):
),
)
# Wire scale → capsfilter → appsink inside a bin so playbin accepts it
# as a single video-sink element.
# Wire queue → 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 scale element's sink pad as the bin's ghost sink pad.
sink_pad = scale.get_static_pad("sink")
# Expose the queue 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")
ghost = self._gst.GhostPad.new("sink", sink_pad)
ghost.set_active(True)
bin_.add_pad(ghost)