Configuring video compression

Setting the compression rate

The image is compressed to reduce the size of the video stream. Video isn't compressed when it is displayed on the video surveillance monitor of the server.

If you increase the compression rate, it leads to video degradation. Axxon PSIM compresses video right after it is digitized by the video capture card before recording and/or transmitting it via the network to the remote workstations.

Set the video compression rate for each camera individually.

Axxon PSIM uses the reverse Discwrite quality (analog camera) parameter for setting the compression rate of the video signal.

In most cases, the default value of the Discwrite quality (analog camera) parameter is sufficient.

If you want to change the compression rate of the video, do the following:

1. Go to the Hardware tab in the System settings window.
2. Select the Camera object created before in the objects tree, which corresponds to the adjusted camera.
3. Select the Basic settings tab on the settings panel of the Camera object.
   

4. To improve the video quality, move the Discwrite quality (analog camera) slider to the max position. To reduce the size of the video stream coming from the camera, move the Discwrite quality (analog camera) slider to the min.

   Note

   Use the video surveillance area to estimate the video quality enhancement or degradation.
5. Click the Apply button.

Setting the key frame rate

Axxon PSIM uses the Motion Wavelet algorithm for video processing and compression. The video that is processed by this algorithm is the sequence of key and delta frames. The key frame is a full frame of an image. The delta frame (differential frame) is an image containing only pixel blocks that differ from the previous key frame.

The Motion Wavelet algorithm guarantees consistency of video quality regardless of the key frame rate. With an increase in motion intensity in the frame, the size of the delta frame increases, and the quality of the video remains unchanged. With very intense motion (more than 70% of the frame is engaged), the setting of the key frame rate is ignored, and each frame is processed as the key frame. 

Axxon PSIM sets the optimal key frame rate value by default: every eighth frame is processed as the key frame. If there are no special requirements for the video size and quality, we recommend keeping the default key frame rate.

To change the key frame rate, do the following:

1. Go to the Hardware tab in the System settings window.
2. Select the Camera object created before in the objects tree, which corresponds to the adjusted camera.
3. Select the Advanced settings tab on the settings panel of the Camera object.
   
4. In the Key frames interval field, specify the required value of the key frame rate.
5. Click the Apply button.

Setting the key frame rate is complete.

Setting the delta frame generation criterion

Axxon PSIM uses the Motion Wavelet algorithm for video processing and compression.

The video that is processed by this algorithm is the sequence of key and delta frames. The key frame is a full frame of an image. The delta frame (differential frame) is an image containing only pixel blocks that differ from the previous key frame. You can compare the pixel blocks of the key frame to the frame that follows the key one by comparing the average brightness of these blocks. If the difference in brightness exceeds the set value, it means that the motion is detected in the block, and this block becomes part of the delta frame. Otherwise, it means that there is no motion in the block, and it isn't included in the delta frame.

The legitimate values of pixel block brightness are in the range from 0 to 225. By default, the block is included in the delta frame if the difference between its average brightness in the current frame and in the previous key frame exceeds seven units. If you increase the value of this parameter, it allows reducing the size of the delta frame and, hence, the size of the video stream, by reducing the number of pixel blocks that form the delta frame. Note that blocks containing the useful motion data in the frame now are more likely to be excluded from the processed video, which consequently leads to video degradation. If you reduce the value of the parameter that sets the criterion for including blocks in the delta frame, it allows improving the video quality by increasing its size.

The optimal value of the parameter that sets the criterion for including blocks in the delta frame is determined by the brightness gradient of the video background and moving objects in the frame. You can increase the parameter value at a high gradient and decrease the parameter value at a low gradient.

To change the value of the parameter that sets the criterion for including blocks of pixels in delta frames, do the following:

1. Go to the Hardware tab in the System settings window.
2. Select the Camera object created before in the objects tree, which corresponds to the adjusted camera.
3. Select the Advanced settings tab on the settings panel of the Camera object.
4. In the Estimate motion field, specify the required value of the parameter that sets the criterion for including blocks of pixels in delta frames.
5. Click the Apply button.

Setting the delta frame generation criterion is complete.