.. _DS_plugin_gst-nvstreammux:

Gst-nvstreammux
================
The Gst-nvstreammux plugin forms a batch of frames from multiple input sources. When connecting a source to nvstreammux (the muxer), a new pad must be requested from the muxer using ``gst_element_get_request_pad()`` and the pad template ``sink_%u``. For more information, see ``link_element_to_streammux_sink_pad()`` in the DeepStream app source code.
The muxer forms a batched buffer of batch-size frames. (batch-size is specified using the gst object property.)
If the muxer’s output format and input format are the same, the muxer forwards the frames from that source as a part of the muxer’s output batched buffer. The frames are returned to the source when muxer gets back its output buffer. If the resolution is not the same, the muxer scales frames from the input into the batched buffer and then returns the input buffers to the upstream component.
The muxer pushes the batch downstream when the batch is filled, or the batch formation timeout batched-pushed-timeout is reached. The timeout starts running when the first buffer for a new batch is collected.
The muxer uses a round-robin algorithm to collect frames from the sources. It tries to collect an average of (batch-size/num-source) frames per batch from each source (if all sources are live and their frame rates are all the same). The number varies for each source, though, depending on the sources’ frame rates.
The muxer outputs a single resolution (i.e. all frames in the batch have the same resolution). This resolution can be specified using the width and height properties. The muxer scales all input frames to this resolution. The enable-padding property can be set to true to preserve the input aspect ratio while scaling by padding with black bands.
For DGPU platforms, the GPU to use for scaling and memory allocations can be specified with the gpu-id property.
For each source that needs scaling to the muxer’s output resolution, the muxer creates a buffer pool and allocates four buffers each of size: ::

     output width*output height*f

Where ``f`` is ``1.5`` for ``NV12`` format, or ``4.0`` for ``RGBA``. The memory type is determined by the ``nvbuf-memory-type`` property.
Set the live-source property to true to inform the muxer that the sources are live. In this case the muxer attaches the PTS of the last copied input buffer to the batched Gst Buffer’s PTS. If the property is set to false, the muxer calculates timestamps based on the frame rate of the source which first negotiates capabilities with the muxer.
The muxer attaches an ``NvDsBatchMeta`` metadata structure to the output batched buffer. This meta contains information about the frames copied into the batch (e.g. source ID of the frame, original resolutions of the input frames, original buffer PTS of the input frames). The source connected to the ``Sink_N`` pad will have ``pad_index`` ``N`` in ``NvDsBatchMeta``.
The muxer supports addition and deletion of sources at run time. When the muxer receives a buffer from a new source, it sends a ``GST_NVEVENT_PAD_ADDED`` event. When a muxer sink pad is removed, the muxer sends a ``GST_NVEVENT_PAD_DELETED`` event. Both events contain the source ID of the source being added or removed (see ``sources/includes/gst-nvevent.h``). Downstream elements can reconfigure when they receive these events. Additionally, the muxer also sends a ``GST_NVEVENT_STREAM_EOS`` to indicate EOS from the source.
The muxer supports calculation of NTP timestamps for source frames. It supports two modes. In the system timestamp mode, the muxer attaches the current system time as NTP timestamp. In the RTCP timestamp mode, the muxer uses RTCP Sender Report to calculate NTP timestamp of the frame when the frame was generated at source. The NTP timestamp is set in ``ntp_timestamp`` field of ``NvDsFrameMeta``. The mode can be toggled by setting the ``attach-sys-ts`` property. For more details, refer to section NTP Timestamp in DeepStream.

.. image:: /content/DS_plugin_gst-nvstreammux.png
         :align: center
         :alt: Gst-nvstreammux

Inputs and Outputs
-----------------------

* Inputs

   * NV12/RGBA buffers from an arbitrary number of sources

* Control Parameters

  *	batch-size
  *	batched-push-timeout
  *	width
  *	height
  *	enable-padding
  *	gpu-id (dGPU only)
  *	live-source
  *	nvbuf-memory-type
  *	num-surfaces-per-frame
  *	buffer-pool-size
  *	attach-sys-ts
  *	frame-duration

* Output

  *	NV12/RGBA batched buffer
  *	GstNvBatchMeta (meta containing information about individual frames in the batched buffer)

Features
----------
The following table summarizes the features of the plugin.

.. csv-table:: Gst-nvstreammux plugin features 
    :file: ../text/tables/Gst-nvstreammux tables/DS_Plugin_gst-nvstreammux_features.csv
    :widths: 30, 30, 30
    :header-rows: 1

.. _DS_plugin_gst_nvstreammux_properties:

Gst Properties
------------------
The following table describes the Gst-nvstreammux plugin’s Gst properties.

.. csv-table:: Gst-nvstreammux gst-properties 
    :file: ../text/tables/Gst-nvstreammux tables/DS_Plugin_gst-nvstreammux_gst-properties.csv
    :widths: 25, 25, 25, 25
    :header-rows: 1