# FAQ¶

## General¶

### What kind of data do we get from a Prophesee sensor?¶

Contrast Detection (CD) events can be acquired from a Prophesee sensor. They represent a response of a pixel to a change of illumination and are of 2 types:

• CD ON events correspond to positive change : from dark to light

• CD OFF events correspond to negative change : from light to dark

### Can I record data from supported cameras? Which format is used for data recording?¶

You can record data with Metavision Player. By default, data are recorded to RAW format. However, Metavision Player allows you to export your recording in AVI format.

In addition, you can convert RAW files to the following formats:

### To avoid flicker events, what non-flickering light source should I use?¶

The best non-flickering light source is any halogen lighting. At Prophesee, we are using DynaSun QL1000 1000 W<https://www.amazon.fr/DynaSun-d%C3%A9clairage-Ventilateur-R%C3%A9gulateur-R%C3%A9flecteur/dp/B005UYO8GS>_. If you want LED source, you must double check it is not flickering (lot of them are using PWM modulation for dimming, and produce flicker). We successfully tested and use Dracast Camlux Pro Bi-Color.

### How do I know what is the event encoding format of a RAW file?¶

You can find the EVT format (EVT2 or EVT3) of your RAW file by one of those methods:

### How can I check the duration and the event rate of my RAW file ?¶

You can use metavision_raw_info application:

metavision_raw_info -i YOUR_FILE.raw


### How can I know the version of Prophesee software installed on my computer?¶

You can retrieve your software version with the metavision_platform_info application.

### Can I use a Virtual Machine (VM) to work with my camera?¶

Prophesee sensors require USB3.0, and due to limited support of USB3.0 by Virtual Machines, your display and USB will not perform as expected, therefore we do not recommend using Virtual Machines.

## Troubleshooting¶

### How can I fix “Entry Point Not Found” when launching Metavision applications?¶

When running Metavision applications on Windows, you may hit the following error message: “Entry Point Not Found. The procedure entry point inflateValidate could not be located in the dynamic link library C:\Program Files\Prophesee\bin\libpng16.dll.”

This means Metavision’s version of libpng is incompatible with some other libraries of your installation. Most probably, there are multiple copies of zlib1.dll in your installation and the first one found by Windows is not ours.

First, check if multiple zlib1.dll can indeed be found in your installation. For this open an explorer and search for zlib1.dll. You should at least have one hit in the folder C:\Program Files\Prophesee\third_party\bin

So now you need to reorder your Path environment variable and move Prophesee Paths first. Here is one way to do it:

• search environment

• select edit environment variables of the system

• click environment variables

• in system variables, locate Path

• edit and reorder the environment variables to have Prophesee Paths at the top

### How to fix the error ‘Failed to load module “canberra-gtk-module”’ on Ubuntu?¶

As explained in the Installation page, you should install the package required to display videos:

sudo apt install libcanberra-gtk-module


### How can I change the logging level at runtime?¶

Metavision uses its own logging mechanism with four levels: DEBUG, TRACE, INFO, WARNING, ERROR. Any message that has a higher or equal level will be enabled to pass through, and any message that has a lower level will be ignored.

The default level (INFO) can be changed by setting the environment variable MV_LOG_LEVEL. This can help you troubleshoot problems. For example, to get a more detailed log (level TRACE):

Linux

export MV_LOG_LEVEL=TRACE


Windows

set MV_LOG_LEVEL=TRACE