gstapp.app_src

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 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. If you don't want to explicitly set the caps, you can use gst_app_src_push_sample. This method gets the caps associated with the sample and sets them on the appsrc replacing any previously set caps (if different from sample's caps).

The main way of handing data to the appsrc element is by calling the [gstapp.app_src.AppSrc.pushBuffer] method or by emitting 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", "max-buffers" and "max-time" properties control 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 emitted, 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 mode, in which the application repeatedly calls the push-buffer/push-sample method with a new buffer/sample. 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/push-sample calls. This is a typical mode of operation for the stream-type "stream" and "seekable". Use this mode when implementing various network protocols or hardware devices.

The pull mode, in which the need-data signal triggers the next push-buffer call. This mode is typically used in the "random-access" stream-type. Use this mode for file access or other randomly accessible 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 has finished pushing data into appsrc, it should call [gstapp.app_src.AppSrc.endOfStream] or emit the end-of-stream action signal. After this call, no more buffers can be pushed into appsrc until a flushing seek occurs or the state of the appsrc has gone through READY.

Fluent builder for [gstapp.app_src.AppSrc]