CaptureCallback

onCaptureBufferLost

open fun onCaptureBufferLost(
    session: CameraCaptureSession, 
    request: CaptureRequest, 
    target: Surface, 
    frameNumber: Long
): Unit

This method is called if a single buffer for a capture could not be sent to its destination surface.

If the whole capture failed, then onCaptureFailed will be called instead. If some but not all buffers were captured but the result metadata will not be available, then onCaptureFailed will be invoked with CaptureFailure#wasImageCaptured returning true, along with one or more calls to onCaptureBufferLost for the failed outputs.

onCaptureCompleted

open fun onCaptureCompleted(
    session: CameraCaptureSession, 
    request: CaptureRequest, 
    result: TotalCaptureResult
): Unit

This method is called when an image capture has fully completed and all the result metadata is available.

This callback will always fire after the last onCaptureProgressed; in other words, no more partial results will be delivered once the completed result is available.

For performance-intensive use-cases where latency is a factor, consider using onCaptureProgressed instead.

The default implementation of this method does nothing.

onCaptureFailed

open fun onCaptureFailed(
    session: CameraCaptureSession, 
    request: CaptureRequest, 
    failure: CaptureFailure
): Unit

This method is called instead of onCaptureCompleted when the camera device failed to produce a CaptureResult for the request.

Other requests are unaffected, and some or all image buffers from the capture may have been pushed to their respective output streams.

If a logical multi-camera fails to generate capture result for one of its physical cameras, this method will be called with a CaptureFailure for that physical camera. In such cases, as long as the logical camera capture result is valid, onCaptureCompleted will still be called.

The default implementation of this method does nothing.

onCaptureProgressed

open fun onCaptureProgressed(
    session: CameraCaptureSession, 
    request: CaptureRequest, 
    partialResult: CaptureResult
): Unit

This method is called when an image capture makes partial forward progress; some (but not all) results from an image capture are available.

The result provided here will contain some subset of the fields of a full result. Multiple onCaptureProgressed calls may happen per capture; a given result field will only be present in one partial capture at most. The final onCaptureCompleted call will always contain all the fields (in particular, the union of all the fields of all the partial results composing the total result).

For each request, some result data might be available earlier than others. The typical delay between each partial result (per request) is a single frame interval. For performance-oriented use-cases, applications should query the metadata they need to make forward progress from the partial results and avoid waiting for the completed result.

For a particular request, onCaptureProgressed may happen before or after onCaptureStarted.

Each request will generate at least 1 partial results, and at most CameraCharacteristics#REQUEST_PARTIAL_RESULT_COUNT partial results.

Depending on the request settings, the number of partial results per request will vary, although typically the partial count could be the same as long as the camera device subsystems enabled stay the same.

The default implementation of this method does nothing.

onCaptureSequenceAborted

open fun onCaptureSequenceAborted(
    session: CameraCaptureSession, 
    sequenceId: Int
): Unit

This method is called independently of the others in CaptureCallback, when a capture sequence aborts before any CaptureResult or CaptureFailure for it have been returned via this listener.

Due to the asynchronous nature of the camera device, not all submitted captures are immediately processed. It is possible to clear out the pending requests by a variety of operations such as CameraCaptureSession#stopRepeating or CameraCaptureSession#abortCaptures. When such an event happens, onCaptureSequenceCompleted will not be called.

The default implementation does nothing.

onCaptureSequenceCompleted

open fun onCaptureSequenceCompleted(
    session: CameraCaptureSession, 
    sequenceId: Int, 
    frameNumber: Long
): Unit

This method is called independently of the others in CaptureCallback, when a capture sequence finishes and all CaptureResult or CaptureFailure for it have been returned via this listener.

In total, there will be at least one result/failure returned by this listener before this callback is invoked. If the capture sequence is aborted before any requests have been processed, onCaptureSequenceAborted is invoked instead.

The default implementation does nothing.

onCaptureStarted

open fun onCaptureStarted(
    session: CameraCaptureSession, 
    request: CaptureRequest, 
    timestamp: Long, 
    frameNumber: Long
): Unit

This method is called when the camera device has started capturing the output image for the request, at the beginning of image exposure, or when the camera device has started processing an input image for a reprocess request.

For a regular capture request, this callback is invoked right as the capture of a frame begins, so it is the most appropriate time for playing a shutter sound, or triggering UI indicators of capture.

The request that is being used for this capture is provided, along with the actual timestamp for the start of exposure. For a reprocess request, this timestamp will be the input image's start of exposure which matches the result timestamp field of the TotalCaptureResult that was used to create the reprocess request. This timestamp matches the timestamps that will be included in the result timestamp field, and in the buffers sent to each output Surface. These buffer timestamps are accessible through, for example, Image.getTimestamp() or android.graphics.SurfaceTexture#getTimestamp(). The frame number included is equal to the frame number that will be included in CaptureResult#getFrameNumber.

For the simplest way to play a shutter sound camera shutter or a video recording start/stop sound, see the android.media.MediaActionSound class.

The default implementation of this method does nothing.

onReadoutStarted

open fun onReadoutStarted(
    session: CameraCaptureSession, 
    request: CaptureRequest, 
    timestamp: Long, 
    frameNumber: Long
): Unit

This method is called when the camera device has started reading out the output image for the request, at the beginning of the sensor image readout.

For a capture request, this callback is invoked right after onCaptureStarted. Unlike onCaptureStarted, instead of passing a timestamp of start of exposure, this callback passes a timestamp of start of camera data readout. This is useful because for a camera running at fixed frame rate, the start of readout is at fixed interval, which is not necessarily true for the start of exposure, particularly when autoexposure is changing exposure duration between frames.

The timestamps match the timestamps of the output surfaces with readout timestamp enabled (via OutputConfiguration#setReadoutTimestampEnabled) if:

• Timestamp base is OutputConfiguration#TIMESTAMP_BASE_DEFAULT and the output
  • is not a SurfaceView surface, and
  • is not a MediaRecoder, MediaCodec, or ImageReader surface with android.hardware.HardwareBuffer#USAGE_VIDEO_ENCODE usage flag or the device's android.hardware.camera2.CameraCharacteristics#SENSOR_INFO_TIMESTAMP_SOURCE is UNKNOWN
• Timestamp base is OutputConfiguration#TIMESTAMP_BASE_SENSOR,
• Timestamp base is OutputConfiguration#TIMESTAMP_BASE_MONOTONIC and the device's CameraCharacteristics#SENSOR_INFO_TIMESTAMP_SOURCE is UNKNOWN,
• Timestamp base is OutputConfiguration#TIMESTAMP_BASE_REALTIME and the device's CameraCharacteristics#SENSOR_INFO_TIMESTAMP_SOURCE is REALTIME

Otherwise, the timestamps won't match the timestamp of the output surfaces. See the possible parameters for OutputConfiguration#setTimestampBase for details.

This callback will be called only if android.hardware.camera2.CameraCharacteristics#SENSOR_READOUT_TIMESTAMP is CameraMetadata#SENSOR_READOUT_TIMESTAMP_HARDWARE, and it's called right after onCaptureStarted.