DxOutputSelector

DxOutputSelector is a GStreamer element used in multi-channel streaming pipelines. It receives a unified stream from DxInputSelector and redistributes the buffers to N output pads based on metadata, such as stream_id.

It is the exit boundary of the multi-stream domain — see Multi-Stream Domain for the overall model.

Key Features

Buffer Routing

• Buffers arriving at the single sink pad are routed to the correct src pad using the stream_id field found in the associated DXFrameMeta.
• This enables seamless demultiplexing of multiple logical video streams within a unified pipeline.
• If stream_id is out of range for the configured number of src pads, the buffer is dropped with a warning and the pipeline continues.

Event Handling

Sink-side events arriving from upstream are classified and dispatched in three ways:

• Domain-wide standard events (STREAM_START, CAPS=application/x-dxvideoraw, SEGMENT, the final global EOS) are consumed at the boundary — the downstream pipeline outside the domain does not receive them. Each output stream's lifecycle is reconstructed from the per-stream wrapped events below.
• Pipeline-wide events (FLUSH_START, FLUSH_STOP, RECONFIGURE) are broadcast to every src pad so that every downstream branch flushes or reconfigures in sync.
• Per-stream wrapped events (application/x-dx-wrapped-event from dxinputselector, carrying the original per-stream STREAM_START, CAPS=video/x-raw, SEGMENT, TAG, EOS, GAP) are unwrapped and forwarded to the src pad whose index matches the wrapped stream-id. This is how each downstream output sees its own original video/x-raw lifecycle.

Upstream QoS

QoS events arriving on a src pad are wrapped with the corresponding stream-id and sent upstream as a CUSTOM_UPSTREAM event. dxinputselector unwraps them and forwards each to the matching sink, so a slow consumer on stream N only throttles its own upstream source — not the other streams.

Hierarchy

GObject
 +----GInitiallyUnowned
       +----GstObject
             +----GstElement
                   +----GstDxOutputSelector

Pad Templates

Sink (input, always pad sink)

Property	Value
Format	application/x-dxvideoraw

Src (output, request pad src_%u)

Property	Value
Format	video/x-raw

Properties

Name	Description	Type	Default Value
name	Sets the unique name of the DxOutputSelector element.	String	"dxoutputselector0"

NOTE

• DxOutputSelector requires asynchronous operation between its upstream and downstream elements. To achieve this, a queue element must be added to each of its src pads. Failure to do so may result in abnormal pipeline hangs.

• The stream_id from the DXFrameMeta of the buffer received on the sink pad is parsed and used as the index of the src pad. If stream_id does not match any configured src pad index, the buffer is dropped with a warning and the pipeline continues.

No global EOS downstream

By design, DxOutputSelector does not forward the domain-wide global EOS to its src pads. Applications that wait for EOS on the bus to terminate the pipeline must not rely on receiving it from the downstream side of DxOutputSelector. Use the per-stream wrapped EOS (unwrapped to the matching src pad) or trigger termination based on application logic (e.g., a timeout, or EOS from another sink).

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