Android APIs
public abstract class

CameraCaptureSession

extends Object
implements AutoCloseable
java.lang.Object
   ↳ android.hardware.camera2.CameraCaptureSession

Class Overview

A configured capture session for a CameraDevice, used for capturing images from the camera.

A CameraCaptureSession is created by providing a set of target output surfaces to createCaptureSession. Once created, the session is active until a new session is created by the camera device, or the camera device is closed.

Creating a session is an expensive operation and can take several hundred milliseconds, since it requires configuring the camera device's internal pipelines and allocating memory buffers for sending images to the desired targets. Therefore the setup is done asynchronously, and createCaptureSession will send the ready-to-use CameraCaptureSession to the provided listener's onConfigured callback. If configuration cannot be completed, then the onConfigureFailed is called, and the session will not become active.

If a new session is created by the camera device, then the previous session is closed, and its associated onClosed callback will be invoked. All of the session methods will throw an IllegalStateException if called once the session is closed.

A closed session clears any repeating requests (as if stopRepeating() had been called), but will still complete all of its in-progress capture requests as normal, before a newly created session takes over and reconfigures the camera device.

Summary

Nested Classes
class CameraCaptureSession.CaptureListener

A listener for tracking the progress of a CaptureRequest submitted to the camera device. 

class CameraCaptureSession.StateListener A listener for tracking the state of a camera capture session. 
Public Constructors
CameraCaptureSession()
Public Methods
abstract void abortCaptures()
Discard all captures currently pending and in-progress as fast as possible.
abstract int capture(CaptureRequest request, CameraCaptureSession.CaptureListener listener, Handler handler)

Submit a request for an image to be captured by the camera device.

abstract int captureBurst(List<CaptureRequest> requests, CameraCaptureSession.CaptureListener listener, Handler handler)
Submit a list of requests to be captured in sequence as a burst.
abstract void close()
Close this capture session asynchronously.
abstract CameraDevice getDevice()
Get the camera device that this session is created for.
abstract int setRepeatingBurst(List<CaptureRequest> requests, CameraCaptureSession.CaptureListener listener, Handler handler)

Request endlessly repeating capture of a sequence of images by this capture session.

abstract int setRepeatingRequest(CaptureRequest request, CameraCaptureSession.CaptureListener listener, Handler handler)
Request endlessly repeating capture of images by this capture session.
abstract void stopRepeating()
[Expand]
Inherited Methods
From class java.lang.Object
From interface java.lang.AutoCloseable

Public Constructors

public CameraCaptureSession ()

Public Methods

public abstract void abortCaptures ()

Discard all captures currently pending and in-progress as fast as possible.

The camera device will discard all of its current work as fast as possible. Some in-flight captures may complete successfully and call onCaptureCompleted(CameraCaptureSession, CaptureRequest, TotalCaptureResult), while others will trigger their onCaptureFailed(CameraCaptureSession, CaptureRequest, CaptureFailure) callbacks. If a repeating request or a repeating burst is set, it will be cleared.

This method is the fastest way to switch the camera device to a new session with createCaptureSession(List, CameraCaptureSession.StateListener, Handler), at the cost of discarding in-progress work. It must be called before the new session is created. Once all pending requests are either completed or thrown away, the onReady(CameraCaptureSession) callback will be called, if the session has not been closed. Otherwise, the onClosed(CameraCaptureSession) callback will be fired when a new session is created by the camera device.

Cancelling will introduce at least a brief pause in the stream of data from the camera device, since once the camera device is emptied, the first new request has to make it through the entire camera pipeline before new output buffers are produced.

This means that using abortCaptures() to simply remove pending requests is not recommended; it's best used for quickly switching output configurations, or for cancelling long in-progress requests (such as a multi-second capture).

Throws
CameraAccessException if the camera device is no longer connected or has encountered a fatal error
IllegalStateException if this session is no longer active, either because the session was explicitly closed, a new session has been created or the camera device has been closed.

public abstract int capture (CaptureRequest request, CameraCaptureSession.CaptureListener listener, Handler handler)

Submit a request for an image to be captured by the camera device.

The request defines all the parameters for capturing the single image, including sensor, lens, flash, and post-processing settings.

Each request will produce one CaptureResult and produce new frames for one or more target Surfaces, set with the CaptureRequest builder's addTarget(Surface) method. The target surfaces (set with addTarget(Surface)) must be a subset of the surfaces provided when this capture session was created.

Multiple requests can be in progress at once. They are processed in first-in, first-out order, with minimal delays between each capture. Requests submitted through this method have higher priority than those submitted through setRepeatingRequest(CaptureRequest, CameraCaptureSession.CaptureListener, Handler) or setRepeatingBurst(List, CameraCaptureSession.CaptureListener, Handler), and will be processed as soon as the current repeat/repeatBurst processing completes.

Parameters
request the settings for this capture
listener The callback object to notify once this request has been processed. If null, no metadata will be produced for this capture, although image data will still be produced.
handler the handler on which the listener should be invoked, or null to use the current thread's looper.
Returns
Throws
CameraAccessException if the camera device is no longer connected or has encountered a fatal error
IllegalStateException if this session is no longer active, either because the session was explicitly closed, a new session has been created or the camera device has been closed.
IllegalArgumentException if the request targets Surfaces that are not configured as outputs for this session. Or if the handler is null, the listener is not null, and the calling thread has no looper.

public abstract int captureBurst (List<CaptureRequest> requests, CameraCaptureSession.CaptureListener listener, Handler handler)

Submit a list of requests to be captured in sequence as a burst. The burst will be captured in the minimum amount of time possible, and will not be interleaved with requests submitted by other capture or repeat calls.

The requests will be captured in order, each capture producing one CaptureResult and image buffers for one or more target surfaces. The target surfaces (set with addTarget(Surface)) must be a subset of the surfaces provided when this capture session was created.

The main difference between this method and simply calling capture(CaptureRequest, CameraCaptureSession.CaptureListener, Handler) repeatedly is that this method guarantees that no other requests will be interspersed with the burst.

Parameters
requests the list of settings for this burst capture
listener The callback object to notify each time one of the requests in the burst has been processed. If null, no metadata will be produced for any requests in this burst, although image data will still be produced.
handler the handler on which the listener should be invoked, or null to use the current thread's looper.
Returns
Throws
CameraAccessException if the camera device is no longer connected or has encountered a fatal error
IllegalStateException if this session is no longer active, either because the session was explicitly closed, a new session has been created or the camera device has been closed.
IllegalArgumentException If the requests target Surfaces not currently configured as outputs. Or if the handler is null, the listener is not null, and the calling thread has no looper.

public abstract void close ()

Close this capture session asynchronously.

Closing a session frees up the target output Surfaces of the session for reuse with either a new session, or to other APIs that can draw to Surfaces.

Note that creating a new capture session with createCaptureSession(List, CameraCaptureSession.StateListener, Handler) will close any existing capture session automatically, and call the older session listener's onClosed(CameraCaptureSession) callback. Using createCaptureSession(List, CameraCaptureSession.StateListener, Handler) directly without closing is the recommended approach for quickly switching to a new session, since unchanged target outputs can be reused more efficiently.

Once a session is closed, all methods on it will throw an IllegalStateException, and any repeating requests or bursts are stopped (as if stopRepeating() was called). However, any in-progress capture requests submitted to the session will be completed as normal; once all captures have completed and the session has been torn down, onClosed(CameraCaptureSession) will be called.

Closing a session is idempotent; closing more than once has no effect.

public abstract CameraDevice getDevice ()

Get the camera device that this session is created for.

public abstract int setRepeatingBurst (List<CaptureRequest> requests, CameraCaptureSession.CaptureListener listener, Handler handler)

Request endlessly repeating capture of a sequence of images by this capture session.

With this method, the camera device will continually capture images, cycling through the settings in the provided list of CaptureRequests, at the maximum rate possible.

If a request is submitted through capture(CaptureRequest, CameraCaptureSession.CaptureListener, Handler) or captureBurst(List, CameraCaptureSession.CaptureListener, Handler), the current repetition of the request list will be completed before the higher-priority request is handled. This guarantees that the application always receives a complete repeat burst captured in minimal time, instead of bursts interleaved with higher-priority captures, or incomplete captures.

Repeating burst requests are a simple way for an application to maintain a preview or other continuous stream of frames where each request is different in a predicatable way, without having to continually submit requests through captureBurst(List, CameraCaptureSession.CaptureListener, Handler).

To stop the repeating capture, call stopRepeating(). Any ongoing burst will still be completed, however. Calling abortCaptures() will also clear the request.

Calling this method will replace a previously-set repeating request or burst set up by this method or setRepeatingRequest(CaptureRequest, CameraCaptureSession.CaptureListener, Handler), although any in-progress burst will be completed before the new repeat burst will be used.

Parameters
requests the list of requests to cycle through indefinitely
listener The callback object to notify each time one of the requests in the repeating bursts has finished processing. If null, no metadata will be produced for this stream of requests, although image data will still be produced.
handler the handler on which the listener should be invoked, or null to use the current thread's looper.
Returns
Throws
CameraAccessException if the camera device is no longer connected or has encountered a fatal error
IllegalStateException if this session is no longer active, either because the session was explicitly closed, a new session has been created or the camera device has been closed.
IllegalArgumentException If the requests reference Surfaces not currently configured as outputs. Or if the handler is null, the listener is not null, and the calling thread has no looper. Or if no requests were passed in.

public abstract int setRepeatingRequest (CaptureRequest request, CameraCaptureSession.CaptureListener listener, Handler handler)

Request endlessly repeating capture of images by this capture session.

With this method, the camera device will continually capture images using the settings in the provided CaptureRequest, at the maximum rate possible.

Repeating requests are a simple way for an application to maintain a preview or other continuous stream of frames, without having to continually submit identical requests through capture(CaptureRequest, CameraCaptureSession.CaptureListener, Handler).

Repeat requests have lower priority than those submitted through capture(CaptureRequest, CameraCaptureSession.CaptureListener, Handler) or captureBurst(List, CameraCaptureSession.CaptureListener, Handler), so if capture(CaptureRequest, CameraCaptureSession.CaptureListener, Handler) is called when a repeating request is active, the capture request will be processed before any further repeating requests are processed.

To stop the repeating capture, call stopRepeating(). Calling abortCaptures() will also clear the request.

Calling this method will replace any earlier repeating request or burst set up by this method or setRepeatingBurst(List, CameraCaptureSession.CaptureListener, Handler), although any in-progress burst will be completed before the new repeat request will be used.

Parameters
request the request to repeat indefinitely
listener The callback object to notify every time the request finishes processing. If null, no metadata will be produced for this stream of requests, although image data will still be produced.
handler the handler on which the listener should be invoked, or null to use the current thread's looper.
Returns
Throws
CameraAccessException if the camera device is no longer connected or has encountered a fatal error
IllegalStateException if this session is no longer active, either because the session was explicitly closed, a new session has been created or the camera device has been closed.
IllegalArgumentException If the requests reference Surfaces that are not currently configured as outputs. Or if the handler is null, the listener is not null, and the calling thread has no looper. Or if no requests were passed in.

public abstract void stopRepeating ()

Cancel any ongoing repeating capture set by either setRepeatingRequest or setRepeatingBurst(List, CameraCaptureSession.CaptureListener, Handler). Has no effect on requests submitted through capture or captureBurst.

Any currently in-flight captures will still complete, as will any burst that is mid-capture. To ensure that the device has finished processing all of its capture requests and is in ready state, wait for the onReady(CameraCaptureSession) callback after calling this method.

Throws
CameraAccessException if the camera device is no longer connected or has encountered a fatal error
IllegalStateException if this session is no longer active, either because the session was explicitly closed, a new session has been created or the camera device has been closed.