Using GStreamer

Introduction

GStreamer is a pipeline-based multimedia framework that links together a wide variety of media processing systems to complete complex workflows. The pipeline design serves as a base to create many types of multimedia applications such as video editors, transcoders, streaming media broadcasters and media players. The Xilinx Video SDK includes an enhanced version of GStreamer which can communicate with the hardware accelerated transcode pipeline in Xilinx devices.

It is not within the scope of this document to provide an exhaustive guide on the usage of GStreamer. Various resources can be found online, for example:

Overview of the GStreamer Plugins

The Xilinx Video SDK provides the following GStreamer plugins for building hardware-accelerated video pipelines using Xilinx devices:

  • vvas_xvcudec for H.264/H.265 decoding

  • vvas_xvcuenc for H.264/H.265 encoding

  • vvas_xabrscaler for hardware accelerated scaling and color conversion

  • vvas_xlookahead for hardware accelerated lookahead

All the GStreamer plugins included in the Xilinx Video SDK are released under the Vitis Video Analytics SDK (VVAS), a framework to build GStreamer-based solutions on Xilinx platforms. Source code and build scripts for the GStreamer plugins developed by Xilinx can be found the in the sources/video-sdk-gstreamer folder of the Xilinx Video SDK repository.

The following sections describe the options used with GStreamer to configure and use the various hardware accelerators available on Xilinx devices.


Decoder Plugin

For the complete list of features and capabilities of the Xilinx hardware decoder, refer to the Video Codec Unit section of the Specs and Features chapter of the documentation.

The vvas_xvcudec plugin provides support for hardware-accelerated H.264/H.265 decoding using Xilinx devices.

Decoder Inputs and Outputs

  • Input: H.264/H.265 encoded stream in byte-stream formats

  • Output: raw NV12 frames with the following requirements:

Decoder Parameters

Property Name

Description
avoid-dynamic-alloc
Avoid dynamic allocation of output buffers
Type: Boolean
Default Value: True
avoid-output-copy
Avoid output frames copy
Avoid output frames copy even when downstream does not support GstVideoMeta metadata
Type: Boolean
Default Value: false
disable-hdr10-sei
Whether to passthrough HDR10/10+ SEI messages or not
Type: Boolean
Default Value: True
dev-idx
Index of the device on which the decoder should be executed
For more details, refer to the section about Working with Multiple Devices
Valid Device index is 0 to 31. Default value is set to -1 intentionally so that user provides the correct device index.
Type: Integer
Range: -1 to 31
Default Value: -1
disable-hdr10-sei
Whether to passthrough HDR10/10+ SEI messages or not
Type: Boolean
Default Value: false
low-latency
Enable low-latency mode
Enabling this mode reduces decoding latency when splitbuff-mode is also enabled. IMPORTANT: This option should not be used with streams containing B frames.
Type: Boolean
Range: true or false
Default Value: false
splitbuff-mode
Configure decoder in split/unsplit input buffer mode
The split buffer mode hands-off buffers to next pipeline stage earlier. Enabling both splitbuff-mode and low-latency reduces decoding latency.
Type: Boolean
Default Value: false
num-entropy-buf
Specifies the number of decoder internal entropy buffers
Used to smooth out entropy decoding performance. Increasing buffering-count increases decoder memory footprint. Set this value to 10 for higher bit-rate use cases, for example uses cases where the bitrate is more than 100 Mb/s.
Type: Unsigned integer
Range: 2 to 10
Default Value: 2
reservation-id
Resource Pool Reservation id
Type: Unsigned Integer64
Range: 0 - 18446744073709551615
Default Value: 0

Decoder Example Pipelines

Refer to the Decoder Pipeline example for an illustration of how to use this plugin.


Encoder Plugin

For the complete list of features and capabilities of the Xilinx hardware encoder, refer to the Video Codec Unit section of the Specs and Features chapter of the documentation.

The vvas_xvcuenc plugin provides support for hardware-accelerated H.264/H.265 encoding using Xilinx devices.

Encoder Inputs and Outputs

  • Input: raw 8-bit (NV12) or 10-bit (NV12_10LE32) video data

  • Output: H264/H265 8-bit/10-bit encoded stream in byte-stream format

Encoder Parameters

Property Name

Description
aspect-ratio
Display aspect ratio of the video sequence to be written in SPS/VUI
Type: Enum
(0): auto - 4:3 for SD video,16:9 for HD video,unspecified for unknown format
(1): 4-3 - 4:3 aspect ratio
(2): 16-9 - 16:9 aspect ratio
(3): none - Aspect ratio information is not present in the stream
Default: 0
b-frames
Number of B-frames between two consecutive P-frames
Type: Unsigned Integer
Range: 0 - 4294967295
Default: 2
Consult the B Frames section for more details on how to use this option.
control-rate
Bitrate control method
Type: Enum
(0): disable - Disable
(1): constant - Constant
(2): variable - Variable
(3): low-latency - Low Latency
Default: 1, “constant”
dev-idx
Index of the device on which the encoder should be executed
For more details, refer to the section about Working with Multiple Devices
Type: Integer
Range: -1 - 31
Default: -1
Valid Device index is 0 to 31. Default value is set to -1 intentionally so that user provides the correct device index.
enable-pipeline
Enable buffer pipelining to improve performance in non zero-copy use cases
Type: Boolean
Default: False
Set this value to True when the encoder on a device receives data from other device
gop-length
Number of frames in a GOP
Distance between two consecutive I frames. Must be a multiple of (b-frames+1)
Type: Unsigned Integer
Range: 0 - 1000
Default: 120
max-bitrate
Max bitrate in Kbps. Only used if control-rate=variable
Type: Unsigned Integer
Range: 0 - 4294967295
Default: 5000
max-qp
Maximum QP value allowed for the rate control
Type: Unsigned Integer
Range: 0 - 51
Default: 51
min-qp
Minimum QP value allowed for the rate control
Type: Unsigned Integer
Range: 0 - 51
Default: 0
num-cores
Number of encoder cores to be used for current stream
If set to 0 (AUTO), the number of encoder cores is automatically determined. Otherwise sets the number of encoder cores to be used.
Type: Unsigned Integer
Range: 0 - 4
Default: 0
num-slices
Number of slices produced for each frame.
Each slice contains one or more complete macroblock/CTU row(s). Slices are distributed over the frame
as regularly as possible.
In low-latency mode:
H.264(AVC): 32
H.265 (HEVC): 22
In normal latency-mode:
H.264(AVC): picture_height/16
H.265(HEVC): minimum of picture_height/32
Type: Unsigned Integer
Range: 1 - 68
Default: 1
periodicity-idr
Periodicity of IDR frames
Type: Unsigned Integer
Range: 0 - 4294967295
Default: 4294967295
qp-mode
QP control mode used by the encoder
Type: Enum
(0): Uniform - Use the same QP for all coding units of the frame
(1): Auto - Let the encoder handle the QP for each coding unit according to its content
(2): ROI - Adjust QP according to the regions of interest defined on each frame.
(3): Relative-load - Use the information gathered in the lookahead to calculate the best QP
Range: 0 - 3
Default: 1 (i.e. auto)
rc-mode
Enable custom rate control mode
To enable custom rate control, the Lookahead must be enabled, and both the Lookahead rc-mode and the Encoder rc-mode parameters must be set to True.
Type: Boolean
Default: True
reservation-id
Resource Pool Reservation id
Type: Unsigned Integer64
Range: 0 - 18446744073709551615
Default: 0
scaling-list
Scaling list mode
Type: Enum
(0): Flat
(1): Default
Range: 0 - 1
Default: 1
slice-qp
Slice QP mode
When RateCtrlMode = CONST_QP the specified QP is applied to all slices.
When RateCtrlMode = CBR the specified QP is used as initial QP
Type: Integer
Range: -1 - 51
Default: -1
target-bitrate
Target bitrate in Kbps. (5000 Kbps = component default)
This property can be changed in all the states of the element including PLAYING state.
Type: Unsigned Integer
Range: 0 - 4294967295
Default: 5000

Encoder Example Pipelines

Refer to the Encoder Pipeline example for an illustration of how to use this plugin.


ABR Scaler Plugin

The vvas_xabrscaler plugin provides support for hardware-accelerated resizing and color space conversion using Xilinx devices. This plugin supports:

  1. Single input multiple output pads

  2. Color space conversion

  3. Resizing

  4. Each output pad has independent configurations, like resolution and color space.

ABR Scaler Inputs and Outputs

  • Input: raw data with 8-bit (NV12) or 10-bit format (NV12_10LE32)

  • Output: raw data with 8-bit (NV12) or 10-bit format (NV12_10LE32)

ABR Scaler Parameters

Property Name

Description
avoid-output-copy
Avoid output frames copy on all source pads
Avoid output frames copy on all source pads even when downstream does not support GstVideoMeta metadata
Type: Boolean
Default Value: false
coef-load-type
coefficients loading type for scaling
Type: Enum
(0): fixed - Use fixed filter coefficients
(1): auto - Auto generate filter coefficients
Default: 1
dev-idx
Index of the device on which the scaler should be executed
For more details, refer to the section about Working with Multiple Devices
Type: Integer
Range: -1 to 31
Default: -1
Valid Device index is 0 to 31. Default value is set to -1 intentionally so that user provides the correct device index
enable-pipeline
Enable buffer pipelining to improve performance in non zero-copy use cases
Type: Boolean
Default: False
Set this value to 1 when the scaler on one device is receiving data from other device
kernel-name
Kernel and instance name
Type: String
Range: Must be set to: scaler:scaler_1
Default: NULL
reservation-id
Resource Pool Reservation id
Type: Unsigned Integer64
Range: 0 - 18446744073709551615
Default Value: 0

ABR Scaler Example Pipelines

Refer to the Transcode with Multiple-Resolution Outputs example for an illustration of how to use this plugin.


Lookahead Plugin

The vvas_xlookahead plugin provides support for hardware-accelerated lookahead functionality using Xilinx devices. This plugin is typically used in conjunction with the encoder plugin to improve the subjective quality of the encoded stream at the cost of latency. The plugin can generate quantization parameters (QP buffer) as well as frame sum of absolute differences and frame activity information (FSFA buffer). The QP and FSFA buffers are attached to the input frame as metadata and sent to next element in the GStreamer media pipeline

Lookahead Inputs and Outputs

  • Accepts raw NV12 frames up to resolution 3840x2160 as input

  • Produces QP and/or FSFA buffers based on the following user controls:

    • QP buffer is generated when the lookahead-depth option is set to a value greater than 0.

    • FSFA buffer is generated when the rc-mode option is enabled.

Lookahead Parameters

Property Name

Description
b-frames
Number of B-frames between two consecutive P-frames
The same setting should be used for the encoder and lookahead plugins. This property can be changed in PAUSED/PLAYING state of the element when the encoder gop-mode is basic.
Type: Unsigned Integer
Range: 0 - 4294967295
Default: 2
codec-type
Codec type H264/H265
The same setting should be used for the encoder and lookahead plugins. Based on the codec type, corresponding metadata will be produced and attached to the input frame
Type: Enum
(0): H264
(1): H265
Range: N/A
Default: None
dev-idx
Index of the device on which the lookahead should be executed
For more details, refer to the section about Working with Multiple Devices
Type: Integer
Range: -1 to 31
Default: -1
Valid Device index is 0 to 31. Default value is set to -1 intentionally so that user provides the correct device index
gop-length
Number of frames between consecutive keyframes. When this is set, same value should be set for encoder plugin as well
Type: Unsigned Integer
Range: 0 to 256
Default: 120
kernel-name
Lookahead kernel name
Type: String
Range: Must be set to: lookahead
Default: NULL
lookahead-depth
Lookahead depth
Type: Unsinged Integer
Range: 1 to 20
Default: 8
rc-mode
Enable custom rate control
To enable custom rate control, the Lookahead must be enabled, and both the Lookahead rc-mode and the Encoder rc-mode parameters must be set to True.
Type: Boolean
Range: N/A
Default: False
reservation-id
Resource Pool Reservation id
Type: Unsigned Integer64
Range: 0 - 18446744073709551615
Default Value: 0
spatial-aq
Enable/Disable Spatial AQ activity
This property can be changed in all the states of the element including PLAYING state.
Type: Boolean
Range: N/A
Default: True
spatial-aq-gain
Percentage of Spatial AQ gain. Applied when enable-spatial-aq is true
This property can be changed in all the states of the element including PLAYING state.
Type: Unsigned Integer
Range: 0 to 100
Default: 50
temporal-aq
Enable/Disable Temporal AQ linear
This property can be changed in all the states of the element including PLAYING state.
Type: Boolean
Range: N/A
Default: True

Lookahead Example pipeline

Refer to the Transcode with Lookahead for Multiple-Resolution outputs example for an illustration of how to use this plugin.

gst-launch-1.0 filesrc location=<input mp4 absolute path> ! qtdemux ! queue ! h264parse ! \
  vvas_xvcudec    dev-idx=0 ! queue ! \
  vvas_xlookahead dev-idx=0 kernel-name=lookahead codec-type=0 spatial-aq=1 temporal-aq=1 lookahead-depth=8 rc-mode=1 ! queue ! \
  vvas_xvcuenc    dev-idx=0 target-bitrate=4000 rc-mode=1 ! \
  h264parse ! "video/x-h264" ! fpsdisplaysink video-sink="fakesink" text-overlay=false sync=false -v

Moving Data through the Pipeline

The GStreamer plugins included in the Xilinx Video SDK take care of efficiently moving data through the video processing pipeline. For optimal performance, video buffers will be moved between the host and the appropriate device only if needed by plugins in the pipeline. This is known as “zero-copy”.

  • The decoder plugin will only copy the output buffer from the device to the host if a downstream element (e.g. filesink) running on the host needs to access the decoded frame. This allows downstream hardware-accelerated plugins (e.g. scaler, encoder) running on the same Xilinx device to process the decoded frames without unnecessary data transfers.

  • The encoder plugin will only copy the input buffer from host to the device if it is allocated in user-space memory on the host or in a different FPGA device. This allows the encoder to process frames produced by upstream hardware-accelerated plugins (e.g. decoder, scaler) running on the same Xilinx device without unnecessary data transfers.


Working with Multiple Devices

By default (if no device identifier is specified) a job is submitted to device 0. When running large jobs or multiple jobs in parallel, device 0 is bound to run out of resources rapidly and additional jobs will error out due to insufficient resources.

By using the dev-idx option of the GStreamer plugins included in the Xilinx Video SDK, the different functions (decoder, scaler, encoder) of a pipeline can be individually submitted to a specific device. This makes it easy and straightforward to leverage the entire video acceleration capacity of your system, regardless of the number of cards and devices.

Consult the Using Explicit Device IDs section for more details on how to work with multiple devices.


Mapping Audio Streams

This section gives examples on how to decode or transcode the input streams with both video and audio

Use MP4 container file with H264 video and MP3/AAC audio. Test both audio and video playback.Decode video using VVAS plugins and audio using open source plugins. Make sure both video and audio playback are in sync.

gst-launch-1.0  filesrc location=<Input MP4 file> \
  ! qtdemux name=demux demux. \
  ! queue \
  ! h264parse \
  ! vvas_xvcudec dev-idx=0 \
  ! autovideosink demux. \
  ! queue \
  ! mpegaudioparse \
  ! avdec_mp3  \
  ! autoaudiosink -v

Use MP4 container file with H265 video and MP3/AAC audio. Test both audio and video playback.Decode video using VVAS plugins and audio using open source plugins. Make sure both video and audio playback are in sync.

gst-launch-1.0  filesrc location=<Input MP4 file> \
 ! qtdemux name=demux demux. \
 ! queue \
 ! h265parse \
 ! vvas_xvcudec dev-idx=0 \
 ! autovideosink demux. \
 ! queue \
 ! mpegaudioparse \
 ! avdec_mp3  \
 ! autoaudiosink -v

Use MP4 container file with H264 video and MP3/AAC audio. Test both audio and video playback. Decode and scale video using VVAS plugins. Make sure to run decoder in one device and scaler on an another device. Decode the audio using opensource plugins. Make sure both video and audio playback are in sync.

gst-launch-1.0 filesrc location=<Input 1080p MP4 file> \
 ! qtdemux name=demux demux. \
 ! queue  \
 ! h264parse \
 ! vvas_xvcudec dev-idx=0 \
 ! vvas_xabrscaler dev-idx=1 ppc=4 scale-mode=2 \
 ! video/x-raw, width=1280, height=720 \
 ! autovideosink demux. \
 ! queue \
 ! mpegaudioparse \
 ! avdec_mp3 \
 ! autoaudiosink -v

Use MP4 container file with H264 Video and AAC/MP3 audio. Transcode only video from H264 to H265 using VVAS plugins and keep audio as it is and mux them back to MP4.

gst-launch-1.0 filesrc location=<1080p60 mp4 with h264 stream> \
 ! qtdemux name=demux qtmux name=mux \
 ! filesink location=output.mp4 demux.video_0 \
 ! queue \
 ! h264parse \
 ! vvas_xvcudec dev-idx=0 \
 ! vvas_xvcuenc dev-idx=0 target-bitrate=2000 \
 ! h265parse \
 ! video/x-h265 \
 ! mux. demux.audio_0 \
 ! queue \
 ! mpegaudioparse \
 !  mux.

When the GStreamer job has multiple outputs, It must be explicitely told which audio stream to map to each of the output streams. The example below implements an transcoding pipeline with an ABR ladder. The input audio stream is split into 4 different channels using qtdemux, one for each video output. The generated transcoded output streams will have both audio and video data.

gst-launch-1.0 filesrc location=~/Akhanda.mp4 \
! qtdemux name=demux demux.video_0 ! queue \
! h264parse \
! vvas_xvcudec  dev-idx=0 ! queue \
! vvas_xabrscaler  dev-idx=0 ppc=4 scale-mode=2 avoid-output-copy=true name=sc_name sc_name.src_0 \
! queue \
! video/x-raw, width=1280, height=720 \
! vvas_xvcuenc name=enc_720p60 dev-idx=0  target-bitrate=3000 \
! h264parse \
! qtmux name=mux1 ! filesink location=/tmp/output1.mp4 demux.audio_0 ! tee name=tee ! queue ! mux1.audio_0 sc_name.src_1 \
! queue \
! video/x-raw, width=848, height=480 \
! vvas_xvcuenc name=enc_480p30 dev-idx=0  target-bitrate=2500 \
! h264parse \
! qtmux name=mux2 ! filesink location=/tmp/output2.mp4 tee. ! queue !  mux2.audio_0 sc_name.src_2 \
! queue \
! video/x-raw, width=640, height=360 \
! vvas_xvcuenc name=enc_360p30 dev-idx=0  target-bitrate=1250 \
! h264parse \
! qtmux name=mux3 ! filesink location=/tmp/output3.mp4 tee. ! queue ! mux3.audio_0 sc_name.src_3 \
! queue \
! video/x-raw, width=288, height=160 \
! vvas_xvcuenc name=enc_160p30 dev-idx=0  target-bitrate=625 \
! h264parse \
! qtmux name=mux4 ! filesink location=/tmp/output4.mp4 tee. ! queue ! mux4.audio_0

Note

Running the GStreamer pipelines with audio demux elements will give errors if run with input streams without audio


Rebuilding GStreamer

Source code and build scripts for the GStreamer plugins developed by Xilinx can be found the in the sources/video-sdk-gstreamer folder of the Xilinx Video SDK repository.

Follow these steps to rebuild GStreamer with the Xilinx Video SDK plugins enabled:

  1. Navigate the top of the Xilinx Video SDK repository:

    cd /path/to/video-sdk

  2. Make sure the sources have been downloaded from the repository:

    git submodule update --init --recursive

  3. Navigate to the directory containing the GStreamer sources:

    cd sources/video-sdk-gstreamer

  4. Download, build, patch and install the GStreamer packages:

    ./install_gst.sh

  5. Clean the Xilinx GStreamer plugin libraries:

    ./clean_vvas.sh

  6. Build and install the Xilinx GStreamer plugins:

    ./build_install_vvas.sh PCIe 1

NOTE: The script sources/video-sdk-gstreamer/install_gst.sh script deletes the source files after the installation. In order to preserve the patched open source GStreamer sources, use the sources/video-sdk-gstreamer/retrieve_gst_sources.sh script. This script clones the open source GStreamer sources and applies the Xilinx specific patches on top of it. The patched sources are available in the following folders:

  • /tmp/gst-libav-1.16.2

  • /tmp/gst-plugins-bad-1.16.2

  • /tmp/gst-plugins-base-1.16.2

  • /tmp/gst-plugins-good-1.16.2

  • /tmp/gstreamer-1.16.2