ALVideoRecorder

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NAOqi Vision - Overview | API | Tutorial


What it does

The ALVideoRecorder module allows you to record video sequences using the robot cameras and save them on disk.

StartRecording and StopRecording

These two functions are used to record videos on the robot.

They are quite straightforward to use. Just call ALVideoRecorderProxy::startRecording passing the video name as argument. The robot will then start to record what it can see with its active camera. The record is done using the module’s parameters (color space, frame rate, resolution, video format). All these parameters can be set using the appropriate methods (see the API section). Please note that the frame rate may go down below the specified value depending on what is running on the robot.

Note

startRecording is not a blocking function, it launches a separate thread that performs the video recording.

When you want to stop the record, call ALVideoRecorderProxy::stopRecording . The record is then saved on the robot in using the file path and name you specified.

Warning

Please note that you can only have one active record at a time. If you want to know if there is an active record, you can call ALVideoRecorderProxy::isRecording .

Note

If you don’t manually set the parameters, the following ones will be used by default:

  • Color space: BGR
  • Frame rate: 15 frames per second (FPS)
  • Resolution: QVGA (320 x 240)
  • Video format: MJPG

Performances and limitations

Depending on the video format used for encoding, the video stream can either be compressed or uncompressed. Uncompressed video has a limited impact on the CPU but produces quite large video files (500MB for a 5-minute video at 10 FPS and VGA resolution).

On the contrary, compressed video takes much smaller disk space but requires more processing power. Depending on the CPU load at the moment of recording, the required frame rate may not be reached. On the current hardware, it is not possible to record a VGA compressed video (MJPG for example) at 30 FPS. As a result, ALVideoRecorder will automatically limit the recording frame rate to 15 FPS in VGA resolution.

Note

A video recorded with MJPG or IYUV format will be stored in an AVI container. As a result, the file name will end with ”.avi”.

Warning

Recording a gray scale video in IYUV is not possible. Either switch to a color video or to another video format (MJPG).

Getting started

The easiest way to get started with most of these features is to use the corresponding Choregraphe vision boxes. Recording capabilities can be easily used through the camera panel of Monitor. You will also find working examples on the Tutorial page.

Video recording can also be quickly accessed using Monitor, which internally uses ALVideoRecorder ‘s functions.