Capture high-speed video

All Oqus cameras with high-speed video capabilities can capture video up to 10000 fps. Oqus high-speed cameras can be recognized by the clear strobe glass, and the second number in the Oqus type is 1, e.g. 310. For a standard Oqus cameras, the video capture rate is limited to 30 Hz and the dark glass filters out the visible light, therefore the video functionality in the standard Oqus is mostly used in preview.

The Oqus camera captures video frames that are synchronized with the marker frames of other cameras in the system, however it is possible to use different capture rate for marker and video. If the Oqus camera has the high-speed functionality it is possible to capture video within the same limitations as the marker capture, so the video and marker capture rates can be the same.

The Oqus video settings are controlled in the Camera settings sidebar or on the Cameras page in Project options dialog, see chapter Camera settings sidebar respectively Cameras.

The recorded video data can be viewed in QTM. The video is stored in AVI format, which can be imported in external video software for further processing or analysis.

Information about high-speed video capture

The following issues should be considered when capturing high-speed video.

  • Lighting
    It is important that there is enough light for recording high-speed video. To capture video data the IR filter has been removed from the Oqus camera, i.e. a clear glass has been mounted. Up to about 60 Hz it is often possible to capture video without extra lighting, however it depends a lot on how light the room is.

    For high speed video, meaning frequencies above 100 Hz, extra lighting is definitely needed. High intensity lamps must be used and with increasing frequency and distance you need more light intensity.

    If you have mounted the external IR filter on the lens that must be removed, so that the visible light is recorded.

  • Data storage
    High-speed video generates a large amount of data. During a capture, the data is buffered in the camera. The maximum amount of data that can be captured is 1.1 GByte. After the capture, the video data is downloaded from the camera, which can take up to about 5 minutes.

    The number of frames that can be captured depends on the frame rate and the image size, see chapter High-speed video. For another resolution multiply the amount of data with the reduced resolution/full resolution.

Outline of how to capture high-speed video

The following outline describes how to capture high-speed video with an Oqus camera.

  1. Switch on the camera system and start QTM.

  2. Open a new file by clicking the New file icon . If you want to use the 3D overlay functionality it is important to check that the camera system has been calibrated.

  3. Switch to 2D view if it is not visible, i.e. right-click in the View window and select Switch to 2D view from the menu.

  4. Right-click on the 2D view for the camera that will capture high-speed video. Select Mode/Video to switch to Video mode. The 2D view for that camera will switch to a video image.

  5. Open the aperture to at least 4 and set the focus.

  6. Change the settings for Video capture in the Camera settings sidebar.

    1. Set the video Capture rate. This can be set independently of the marker image rate.

      The image size is reduced automatically when it is changed on the Camera settings sidebar.

    2. Set the Exposure time to a value that makes the image bright enough, test until you are satisfied.

      If you have no extra light the exposure time needs to be quite high, at least 16000 microseconds or even up to 40000. This limits the capture rate that can be used. It also means that fast movements will be blurred.

      For high capture rates and measurements with fast movement, extra lighting is needed because the exposure time must be extremely short, sometimes as short as 100 microseconds.

      Use a Codec if you want to reduce the size of the avi-files. If the file will be used in analysis it must not be reduced too much as it can influence the analysis.

      The codec does not change the download speed since it is applied after downloading the raw video.

      The Image format will reduce the image directly in the camera, but then you will lose pixels.

  7. A video capture takes about a second to initialize so it is recommended that you use external trigger and pretrigger to start the capture. For the settings, see chapter Synchronization.

  8. Click the Capture icon and set the capture time and other capture settings. Keep the capture time as short as possible to reduce the fetching time.

  9. Click OK and then press the trigger button when you want to start the measurement.

  10. Wait for the fetching of video data to finish. Depending on how large file you have captured and the number of cameras, it can take up to some minutes to fetch the data.

  11. The video file is displayed in the 2D view window and can be played in synchronization with other data.

    If the video data is uncompressed it is not possible to play the file in normal speed as the video playback will be too slow. Then it is better to step through the file instead.

Codecs for Oqus high-speed video files

A codec can be used to significantly reduce the file size of the high-speed video files. Any codec that can run on Microsoft DirectShow can be used in QTM to compress Oqus high-speed video files. There are many codecs available. For a selection of recommended codecs that have been tested with QTM, see the list below.

Lossless codecs keeps all original image information in the files which makes them suitable for high quality video analysis. Lossy codec removes information, usually based on what the human eye can register, which makes a video compressed with a lossy codec suitable for movie encoding.

The codec of the high-speed video file must be set before the measurement is started, either by right-clicking on an Oqus camera in Video mode or with the Video compression settings on the Cameras page in the Project options dialog. It is not possible to compress a saved video file in QTM. However, QTM will still be able to play the file if it is compressed in another program.

Even for the codecs we recommend we will not guarantee that the files can be played in any program, even if the codec is installed on the computer. This is because every program is a little bit different in how they play the file and it is impossible for us to test all of the settings and configuration. Therefore we recommend that you make tests with the codec before making the measurements.

Recommended codecs

For a list of current recommended codecs and download links, see https://www.qualisys.com/info/recommended-codecs/. More information about the codecs:

Lagarith

  • A lossless codec with a typical compression of 4-8 times. The codec uses arithmetic and RLE encoding.

  • In QTM the files can be played close to the original speed.

BlackMagic/Decklink MJPEG

  • A lossy codec using JPEG compression of each video frame.

  • The codecs are included with BlackMagic Desktop Video software. The software can be installed, even when you do not have a BlackMagic design video interface.

  • For the latest version tested with QTM, use the download link provided at https://www.qualisys.com/info/recommended-codecs/.

    • On the BlackMagic design download page, you can click the Download Only link to download the software without registration.

FFDS (MJPEG)

  • The FFDShow MJPEG codec, which was previously included with QTM, has been discontinued.

  • The FFDS MJPEG can be used with QTM version 2023.3 or earlier. For detailed instructions, see the manual included with the specific QTM installation.

  • For QTM 2024.1 or later, the BlackMagic/Decklink MJPEG codec is recommended.