Vala Binding Reference

AppSink - Appsink is a sink plugin that supports many different methods for making the application get a handle on the GStreamer data in a pipeline. Unlike most GStreamer elements, Appsink provides external API functions. appsink can be used by linking to the gstappsink.h header file to access the methods or by using the appsink action signals and properties. The normal way of retrieving buffers from appsink is by using the pull_buffer and pull_preroll methods. These methods block until a buffer becomes available in the sink or when the sink is shut down or reaches EOS. Appsink will internally use a queue to collect buffers from the streaming thread. If the application is not pulling buffers fast enough, this queue will consume a lot of memory over time. The "max-buffers" property can be used to limit the queue size. The "drop" property controls whether the streaming thread blocks or if older buffers are dropped when the maximum queue size is reached. Note that blocking the streaming thread can negatively affect real-time performance and should be avoided. If a blocking behaviour is not desirable, setting the "emit-signals" property to true will make appsink emit the "new-buffer" and "new-preroll" signals when a buffer can be pulled without blocking. The "caps" property on appsink can be used to control the formats that appsink can receive. This property can contain non-fixed caps, the format of the pulled buffers can be obtained by getting the buffer caps. If one of the pull-preroll or pull-buffer methods return null, the appsink is stopped or in the EOS state. You can check for the EOS state with the "eos" property or with the is_eos method. The eos signal can also be used to be informed when the EOS state is reached to avoid polling. Last reviewed on 2008-12-17 (0.10.22)

AppSinkCallbacks - A set of callbacks that can be installed on the appsink with set_callbacks.

AppSrc - The appsrc element can be used by applications to insert data into a GStreamer pipeline. Unlike most GStreamer elements, Appsrc provides external API functions. appsrc can be used by linking with the libgstapp library to access the methods directly or by using the appsrc action signals. Before operating appsrc, the caps property must be set to a fixed caps describing the format of the data that will be pushed with appsrc. An exception to this is when pushing buffers with unknown caps, in which case no caps should be set. This is typically true of file-like sources that push raw byte buffers. The main way of handing data to the appsrc element is by calling the push_buffer method or by emiting the push-buffer action signal. This will put the buffer onto a queue from which appsrc will read from in its streaming thread. It is important to note that data transport will not happen from the thread that performed the push-buffer call. The "max-bytes" property controls how much data can be queued in appsrc before appsrc considers the queue full. A filled internal queue will always signal the "enough-data" signal, which signals the application that it should stop pushing data into appsrc. The "block" property will cause appsrc to block the push-buffer method until free data becomes available again. When the internal queue is running out of data, the "need-data" signal is emited, which signals the application that it should start pushing more data into appsrc. In addition to the "need-data" and "enough-data" signals, appsrc can emit the "seek-data" signal when the "stream-mode" property is set to "seekable" or "random-access". The signal argument will contain the new desired position in the stream expressed in the unit set with the "format" property. After receiving the seek-data signal, the application should push-buffers from the new position. These signals allow the application to operate the appsrc in two different ways: The push model, in which the application repeadedly calls the push-buffer method with a new buffer. Optionally, the queue size in the appsrc can be controlled with the enough-data and need-data signals by respectively stopping/starting the push-buffer calls. This is a typical mode of operation for the stream-type "stream" and "seekable". Use this model when implementing various network protocols or hardware devices. The pull model where the need-data signal triggers the next push-buffer call. This mode is typically used in the "random-access" stream-type. Use this model for file access or other randomly accessable sources. In this mode, a buffer of exactly the amount of bytes given by the need-data signal should be pushed into appsrc. In all modes, the size property on appsrc should contain the total stream size in bytes. Setting this property is mandatory in the random-access mode. For the stream and seekable modes, setting this property is optional but recommended. When the application is finished pushing data into appsrc, it should call end_of_stream or emit the end-of-stream action signal. After this call, no more buffers can be pushed into appsrc until a flushing seek happened or the state of the appsrc has gone through READY. Last reviewed on 2008-12-17 (0.10.10)

AppSrcCallbacks - A set of callbacks that can be installed on the appsrc with set_callbacks.

gstreamer-app-0.10

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