DxVnpuDec

DxVnpuDec is an element that decodes H.264/H.265 bitstreams using the DEEPX VNPU hardware decoder.
It outputs raw video frames in NV12, RGB, or BGR format with optional resolution scaling.

Build Requirement

This element is only available when built with the --dxvnpu flag: ./build.sh --dxvnpu

Autoplugging (decodebin)

DxVnpuDec's element rank is set dynamically at plugin initialization based on VNPU device availability:

Condition	Rank	Behavior
VNPU device present	GST_RANK_PRIMARY + 1	Preferred over SW decoders (e.g., avdec_h264) by decodebin
No VNPU device	GST_RANK_NONE	Excluded from autoplugging candidates

When VNPU hardware is available, decodebin will automatically select DxVnpuDec without any explicit configuration.

# decodebin automatically selects dxvnpudec on VNPU-equipped systems
gst-launch-1.0 filesrc location=input.mp4 ! qtdemux ! decodebin ! videoconvert ! autovideosink

Property Limitations

When autoplugged by decodebin, the output-format, output-width, and output-height properties cannot be configured — the decoder will always output NV12 at the original resolution (the default values). These properties are not controllable via downstream caps negotiation either, as the decoder resolves them internally from its own property values, not from downstream caps. To use custom output settings, instantiate dxvnpudec explicitly in the pipeline.

Key Features

Hardware Decoding
Decodes H.264 (AVC) and H.265 (HEVC) bitstreams entirely on the VNPU device, offloading the CPU.

Output Format Selection
The decoded output format can be configured via the output-format property. Supported formats: NV12 (default), RGB, BGR.

Resolution Scaling
The decoder can optionally scale the output to a specified resolution using output-width and output-height properties. When set to 0 (default), the output matches the input resolution.

Hierarchy

GObject
 +----GInitiallyUnowned
       +----GstObject
             +----GstElement
                   +----GstVideoDecoder
                         +----GstDxVnpuDec

Pad Templates

Sink (input)

Property	Value
Format	video/x-h264, stream-format=(string)byte-stream, alignment=(string)au
	video/x-h265, stream-format=(string)byte-stream, alignment=(string)au

Src (output)

Property	Value
Format	video/x-raw, format=(string){ NV12, RGB, BGR }

Properties

Name	Description	Type	Default Value	Range
output-format	Output pixel format from the hardware decoder.	Enum (NV12, RGB, BGR)	NV12	-
output-width	Output width. 0 = same as input.	Integer	0	0 – 8192
output-height	Output height. 0 = same as input.	Integer	0	0 – 8192

Usage Example

Decode an H.264 file and display:

gst-launch-1.0 \
  filesrc location=input.h264 ! h264parse ! \
  dxvnpudec output-format=NV12 ! \
  videoconvert ! autovideosink

Decode and scale to 640x480 BGR:

gst-launch-1.0 \
  filesrc location=input.mp4 ! parsebin ! \
  dxvnpudec output-format=BGR output-width=640 output-height=480 ! \
  appsink

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