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179 lines
6.7 KiB
Markdown
179 lines
6.7 KiB
Markdown
# Basic tutorial 16: Platform-specific elements
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## Goal
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Even though GStreamer is a multiplatform framework, not all the elements
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are available on all platforms. For example, the video sinks
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depend heavily on the underlying windowing system, and a different one
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needs to be selected depending on the platform. You normally do not need
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to worry about this when using elements like `playbin` or
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`autovideosink`, but, for those cases when you need to use one of the
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sinks that are only available on specific platforms, this tutorial hints
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you some of their peculiarities.
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## Cross Platform
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### `glimagesink`
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This video sink is based on
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[OpenGL](http://en.wikipedia.org/wiki/OpenGL) or [OpenGL ES](https://en.wikipedia.org/wiki/OpenGL_ES). It supports rescaling
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and filtering of the scaled image to alleviate aliasing. It implements
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the VideoOverlay interface, so the video window can be re-parented
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(embedded inside other windows). This is the video sink recommended on
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most platforms. In particular, on Android and iOS, it is the only
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available video sink. It can be decomposed into
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`glupload ! glcolorconvert ! glimagesinkelement` to insert further OpenGL
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hardware accelerated processing into the pipeline.
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## Linux
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### `ximagesink`
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A standard RGB only X-based video sink. It implements the VideoOverlay
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interface, so the video window can be re-parented (embedded inside
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other windows). It does not support scaling or color formats other
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than RGB; it has to be performed by different means (using the
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`videoscale` element, for example).
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### `xvimagesink`
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An X-based video sink, using the [X Video
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Extension](http://en.wikipedia.org/wiki/X_video_extension) (Xv). It
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implements the VideoOverlay interface, so the video window can be
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re-parented (embedded inside other windows). It can perform scaling
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efficiently, on the GPU. It is only available if the hardware and
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corresponding drivers support the Xv extension.
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### `alsasink`
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This audio sink outputs to the sound card via
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[ALSA](http://www.alsa-project.org/) (Advanced Linux Sound
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Architecture). This sink is available on almost every Linux platform. It
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is often seen as a “low level” interface to the sound card, and can be
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complicated to configure (See the comment on
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[](sdk-playback-tutorial-digital-audio-pass-through.md)).
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### `pulsesink`
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This sink plays audio to a [PulseAudio](http://www.pulseaudio.org/)
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server. It is a higher level abstraction of the sound card than ALSA,
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and is therefore easier to use and offers more advanced features. It has
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been known to be unstable on some older Linux distributions, though.
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## Mac OS X
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### `osxvideosink`
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This is the video sink available to GStreamer on Mac OS X. It is also
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possible to draw using `glimagesink` using OpenGL.
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### `osxaudiosink`
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This is the only audio sink available to GStreamer on Mac OS X.
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## Windows
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### `directdrawsink`
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This is the oldest of the Windows video sinks, based on [Direct
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Draw](http://en.wikipedia.org/wiki/DirectDraw). It requires DirectX 7,
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so it is available on almost every current Windows platform. It supports
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rescaling and filtering of the scaled image to alleviate aliasing.
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### `dshowvideosink`
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This video sink is based on [Direct
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Show](http://en.wikipedia.org/wiki/Direct_Show). It can use different
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rendering back-ends, like
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[EVR](http://en.wikipedia.org/wiki/Enhanced_Video_Renderer),
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[VMR9](http://en.wikipedia.org/wiki/Direct_Show#Video_rendering_filters)
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or
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[VMR7](http://en.wikipedia.org/wiki/Direct_Show#Video_rendering_filters),
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EVR only being available on Windows Vista or more recent. It supports
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rescaling and filtering of the scaled image to alleviate aliasing. It
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implements the VideoOverlay interface, so the video window can be
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re-parented (embedded inside other windows).
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### `d3dvideosink`
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This video sink is based on
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[Direct3D](http://en.wikipedia.org/wiki/Direct3D) and it’s the most
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recent Windows video sink. It supports rescaling and filtering of the
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scaled image to alleviate aliasing. It implements the VideoOverlay
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interface, so the video window can be re-parented (embedded inside other
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windows).
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### `directsoundsink`
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This is the default audio sink for Windows, based on [Direct
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Sound](http://en.wikipedia.org/wiki/DirectSound), which is available in
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all Windows versions.
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### `dshowdecwrapper`
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[Direct Show](http://en.wikipedia.org/wiki/Direct_Show) is a multimedia
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framework similar to GStreamer. They are different enough, though, so
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that their pipelines cannot be interconnected. However, through this
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element, GStreamer can benefit from the decoding elements present in
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Direct Show. `dshowdecwrapper` wraps multiple Direct Show decoders so
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they can be embedded in a GStreamer pipeline. Use the `gst-inspect-1.0` tool
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(see [](sdk-basic-tutorial-gstreamer-tools.md)) to see the
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available decoders.
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## Android
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### `openslessink`
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This is the only audio sink available to GStreamer on Android. It is
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based on [OpenSL ES](http://en.wikipedia.org/wiki/OpenSL_ES).
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### `openslessrc`
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This is the only audio source available to GStreamer on Android. It is
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based on [OpenSL ES](http://en.wikipedia.org/wiki/OpenSL_ES).
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### `androidmedia`
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[android.media.MediaCodec](http://developer.android.com/reference/android/media/MediaCodec.html)
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is an Android specific API to access the codecs that are available on
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the device, including hardware codecs. It is available since API level
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16 (JellyBean) and GStreamer can use it via the androidmedia plugin
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for audio and video decoding. On Android, attaching the hardware
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decoder to the `glimagesink` element can produce a high performance
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zero-copy decodebin pipeline.
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### `ahcsrc`
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This video source can capture from the cameras on Android devices, it is part
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of the androidmedia plugin and uses the [android.hardware.Camera API](https://developer.android.com/reference/android/hardware/Camera.html).
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## iOS
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### `osxaudiosink`
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This is the only audio sink available to GStreamer on iOS.
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### `iosassetsrc`
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Source element to read iOS assets, this is, documents stored in the
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Library (like photos, music and videos). It can be instantiated
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automatically by `playbin` when URIs use the
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`assets-library://` scheme.
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### `iosavassetsrc`
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Source element to read and decode iOS audiovisual assets, this is,
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documents stored in the Library (like photos, music and videos). It can
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be instantiated automatically by `playbin` when URIs use the
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`ipod-library://` scheme. Decoding is performed by the system, so
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dedicated hardware will be used if available.
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## Conclusion
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This tutorial has shown a few specific details about some GStreamer
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elements which are not available on all platforms. You do not have to
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worry about them when using multiplatform elements like `playbin` or
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`autovideosink`, but it is good to know their personal quirks if
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instancing them manually.
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It has been a pleasure having you here, and see you soon!
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