NVDA screen reader

Before listening to/or reading the following tutorials, please make sure you get your copy of NVDA

Before looking at the following tutorials, make sure you have downloaded a copy of the NVDA screen reader. To get the latest copy, please visit http://www.nvaccess.org and go to the downloads link. Download the programme and set it up. Down the track, if you feel you have benefited from NVDA, then donations (no matter how big or small) are always welcome to keep the project free for everyone!

Training material and phone support for NVDA from the NV Access online shop

Are you aware that NV Access have put together an online Shop where you can buy training material for the NVDA screen reader?
You can also get phone support.

Please stay tuned for more training material as it becomes available.
For more information please visit the NV Access Online Shop at the following link https://www.nvaccess.org/shop/

NVDA expert certification

To find an NVDA certified expert near you, please visit the following link https://certification.nvaccess.org/. The certification page contains the official list of NVDA certified individuals from around the world, who have sat and successfully passed the NVDA expert exam.

Have you got a good grasp on the NVDA screen reader? Have you got what it takes to sit the NVDA expert exam? You can test your knowledge for free. If you pass the exam in the required time frame, then you can purchase an official certificate and be acknowledged on the above webpage under the list of worldwide NVDA experts.

Find out about NVDA progress via the nvaccess In Process blog

To find out what is happening within the NVDA project, visit “In-Process” - the new NV Access blog, where you can be informed of happenings within the organisation, staff and of course, NVDA.

Click on any of the links in the table below, to visit other NVDA related webpages that may be of interest to you.

NVDA related webpages


screen reader

How to install
additional NVDA components

NVDA user statistics

NVDA screen reader related resources

For a variety of NVDA related resources from around the world, please visit the NVDA screen reader related resources page at the following link
NVDA screen reader related resources

What is a screen reader?

A screen reader is a programme which reads the text on a computer screen to a blind or visually impaired person. A screen reader also assists people who learn more efficiently by hearing (for example dyslexics and speakers of other languages).

What does NVDA stand for?

NVDA stands for Non visual desktop access. NVDA can be used both on-line and off-line.

What does it cost?

NVDA is a totally free, open source screen reader. The project however always welcomes any donations (no matter how large or small) to assist them to continually develop the screen reader. The two main developers James Teh and Michael Curran work fulltime on the project and so estimate the project to be about $200,000 AUD annually (to be able to continue development in a fulltime capacity and cover overheads). If you are in a position to donate, please do! This screen reader has benefited more than just the blind community. It has also given freedom to many dyslexic learners and those who may not necessarily have been able to afford expensive commercial screen readers, yet who have benefited from the speech output features of NVDA. Mick and Jamie are keen to keep the project free of cost, and so I would encourage all those who can - to get behind this worthwhile project - and therefore allow others to enjoy the freedom we have experienced with NVDA.

Requirements to run the NVDA screen reader

As of NVDA version 2017.3 there will no longer be support for older versions of Windows such as XP and Vista. The minimum requirements will be

Windows 7, Service Pack 1 and above. Please see the following link for more information https://www.nvaccess.org/post/nvda-2017-4-drops-support-for-older-operating-systems/

To run NVDA you will require the following:

Miscellaneous recent developments

NVDA website

The new home of the free open source NVDA screen reader can be found at the following link http://www.nvaccess.org/  NVDA is now located on the NVaccess website (which is the non profit organisation behind the NVDA screen reader). This allows people to learn more about NVaccess. Please click on this link should you wish to contact them, download a copy of the NVDA screen reader, or simply find out more information. 

NVDA is realeased 4 times a year. This is usually around Feb 23rd, May 23rd, August 23rd and November 23rd if the process goes well. Your copy of NVDA should also alert you about these releases, as long as they don't have the "Automatically check for updates to NVDA" box unchecked under the General settings in NVDA. The installer copy will install over itself, whereas this can't be done with the portable copy.

The NVDA communities main webpage has now moved to GitHub. The page can be found at the following link https://github.com/nvaccess/nvda

NVDA user statistics - daily averages

To see how many people are using NVDA (at a days glance) please visit http://community.nvda-project.org/usersByCountry.html for more information. The number of users given may actually be higher than this, due to having the update feature turned off. It may also be higher than this figure due to not having the internet on that particular computer. Please make sure to read right to the end of the page to get a full breakdown of everything.

Welcome to the NVDA community - links to other NVDA users, articles, tutorials, bug reporting, feature requests, testing, translating and development

The old NVDA screen reader website has also been revamped. What would you like to do? Connect with other NVDA users right around the world; Access articles, tutorials and demonstrations about NVDA; Report a bug or request a feature; Help test NVDA; Translate NVDA into another language; or Get involved with NVDA development? Please visit the following website at http://community.nvda-project.org/ Alternatively you can go to the new website http://www.nvaccess.org/ and look under the community link towards the bottom of the page.

Promotional video on the NVDA screen reader

If you are unsure what a screen reader is, please click on the following link to listen to a promotional video on the NVDA screen reader https://www.youtube.com/watch?v=Ks7AwV_uxO0&feature=youtu.be   Please feel free to pass this information onto others that you think may be interested or who may want to find out more.

To connect with the NVDA community

Visit the following link to connect with the NVDA community http://community.nvda-project.org/wiki/Connect
To join the English users' mailing list, send a blank email to: nvda-request@freelists.org with the word "subscribe" in the subject line.
For a variety of other language's communities/email lists/forums and websites please visit the list below on that same page entitled "Resources for Specific languages".

Translating NVDA into your language

Have you ever thought about translating NVDA into your own language? Visit the following link to see which languages are currently being worked on and which ones you may be able to assist with. You may even be able to translate a language that has not been done yet for other people in your country to be able to use NVDA! For more information please visit the following link https://github.com/nvaccess/nvda/wiki/Translating

Vocalizer voices by Nuance for use with NVDA

NV Access is very happy to announce the availability of the Nuance Vocalizer range of voices for NVDA. These voices, which have proven to be popular on iPhones and the Mac, can now all be purchased for one affordable price for use with NVDA. Whether you use NVDA installed on one computer, or carry it around with you for access at anytime on a USB flash drive, these performant and high-quality voices will be there when you need them.

Purchasing Vocalizer today for 75 EUR gives you access to over 50 different voices covering more than 30 major languages. Vocalizer can be purchased world-wide from  Tiflotecnia Lda. For each purchase 15 EUR will be donated to NV Access to help the NVDA project continue. Purchases can also be made through a range of local distributors, of which 10 EUR will be donated to the project.
For more information about Vocalizer with NVDA, trial downloads and a list of distributors, please visit https://vocalizer-nvda.com/?

To use Vocalizer, NVDA 2012.2 or higher is required. Please visit https://vocalizer-nvda.com/? to grab the latest version if you have not done so already.

The new SpeechHub synthesiser package (by Bill and Isaac)

There is a new synthesiser package that can be used with NVDA. It allows different synthesiser packages to be bundled into the one package and this in turn means you don't have to go looking for them. The new SpeechHub package can be found at http://www.speechhub.org Please read the directions on how to install the package and also acquire the SpeechHub add-on to make the package work.

NVDA screen reader installed on Auckland Libraries network

If you are up in the Auckland area you can use NVDA at any one of the 55 locations at https://www.aucklandlibraries.govt.nz/Pages/locations-and-hours.aspx

You can also see that the NVDA screen reader is installed on their software page at https://www.aucklandlibraries.govt.nz/Pages/computer-use.aspx
At present, you will need to ask a librarian to sign you in to the network, then start NVDA for you.

Auckland Libraries network have about 600 public computers across 55 locations.

To access NVDA, once the librarian has signed you in to the computer, they can either start NVDA for you; or to do it yourself...Press Ctrl + Esc simultaneously. Once you have done that, type in NVDA. It should show as the third link listed in your search results. Press the down arrow key three times, and then press Enter to select and launch it.

NVDA screen reader installed on Christchurch City Libraries network December 2018

Christchurch City Library announces the installation of the NVDA screen reader on 390 of their public terminals across their network of 19 libraries. To find out which software is available on the CCL network, and how to start the NVDA screen reader, please go to the following links. Software available  https://my.christchurchcitylibraries.com/faq/computers/#faq_5884  How to start the NVDA screen reader on Christchurch City Library computers  https://my.christchurchcitylibraries.com/faqs/what-screen-reader-software-is-available/

Who invented NVDA?

NVDA was originally created by Michael Curran (in 2006) and had been constantly developed with the part time assistance of James Teh. In February 2008 James became a full-time developer for the project. Mick and Jamie are both blind Australian computer programmers, who wanted to see the screen reader market opened up; so that a lot more people could have accessibility, without the extraordinary costs generally associated with such adaptive technology. Since the creation and development of NVDA, people who require a screen reader can now have equal access for no more than the cost of a PC. Traditionally, people used to have to purchase a computer, add onto that the high cost of a commercial screen reader, and any subsequent upgrades they required. Now, it is simply a matter of purchasing a computer and downloading and setting up the free screen reader software. The invention of a free, open source, reliable screen reader has opened up the doors for many people.

Advantages of the NVDA screen reader

Running NVDA on Windows 8 devices

Please note. If you are thinking of using NVDA on a Windows 8 device, NVDA will not work on a Windows 8 (RT) device however, NVDA will work on a Windows 8 (x86) device. 

Please click on the following link to find out more information about the difference between Windows 8 (x86) and Windows 8 (RT) versions http://www.techradar.com/news/software/operating-systems/windows-8-vs-windows-rt-what-s-the-difference-1086980

Downloading, installing and creating hard drive, portable USB and CD rom copies of NVDA

When you first download the new NVDA package, those who have used NVDA before will notice some changes. In previous versions there was an installer version as well as a separate portable version. These have now been combined into the one package, making it easier for the developers to maintain.

Once the new package has been downloaded (and then clicked on to start the setup), it will run a talking installer.  When you have agreed to the licence you will be given three options. The first option will be to make an installer version. (This version will be installed to your C:\ drive). The second option will be to make a portable version.  (This is where you can put it onto a USB stick or a CD).   
The third option will be to run a temporary copy of NVDA (either to give it a whirl or to demonstrate it as a demo without installing anything).

In most cases when you are installing NVDA for the first time, you will just install a hard drive copy (also known as an installer copy) to the C:\ drive.

At a later date, if you have installed the installer version, you can always make a portable version from this.  This option can be found under the preferences/tools menu. You will be looking for a menu called create portable copy, then it will be a matter of following the directions to make one.

You can also (from that portable copy) either install a copy to the C:\ drive (this will be the installer version) or make another portable version. Most people will use the installer version (which will give you UAC privileges as well - which Windows now uses in Windows 7).
Both of these options are found under the preferences/tools section within NVDA portable. The two options available are called: Create portable copy and Install NVDA.

To create a portable version of NVDA from the installer version for a USB stick

If you have already installed NVDA to your C:\ drive and would like to make a portable copy for a USB stick, there are 2 ways you can do it. Under the preferences/tools section within NVDA, locate the menu that says create portable copy, and press enter. The next screen that comes up will let you browse for an area to create the portable copy in. The easiest way is either to put a copy onto your C:\ drive, or to put a copy onto your USB stick.

To put a copy onto your C:\ find the browse button and press enter. Once you have located your C:\ create a new folder and rename it NVDA. Once this has been done, follow the directions until the contents are installed into that directory. When you look at it (at a later date on your C:\) it should look like this (for example) C:\nvda  To put a copy onto your USB stick, insert the USB stick and it should be assigned a letter (for example E:\). Next, go back to the C: and locate your NVDA folder and copy and paste it onto your USB stick. When you look at it (at a later date on your E:\) it should look like this (for example) E:\nvda if there are no other files or folders on that USB stick. If you do plan to have other files and folders on your USB stick, put them into a folder on that stick called useful stuff or some other easily identifiable name. Do not use any other folders or files starting with the letter N (so that when you go to open the USB stick, you will be able to press N and it will only look at the NVDA folder). Having other files or folders starting with the letter N will make it look at them first. Finally, unplug the USB stick and plug it back into a USB hole. An autorun menu should come up giving you some options. Press the letter O to open the folder, press enter, then press the letter N to find the NVDA directory and press enter again. Press the letter N again and it should find the nvda.exe file and NVDA should start up.

The second option is to copy it straight to the USB stick. To do this, under the preferences/tools section within NVDA, locate the menu that says create portable copy and press enter. Locate the browse button, press enter, and locate your USB stick drive letter (for example this may be E:\). Once you have located your USB drive, create a new folder, rename it NVDA, press enter and follow the directions on how to install it to your USB stick. Once this has been done, unplug your USB stick and plug it back into a USB hole. An autorun menu should come up giving you some options. Press the letter O to open the folder, press enter, then press the letter N to find the NVDA directory and press enter again. Press the letter N again and it should find the nvda.exe file and NVDA should start up.

To create a portable version of NVDA to put onto a CD

The easiest way to do this, is to create a directory on your C:\ and call it nvda portable copy for a CD (or something similar to that effect). In this directory, will go the NVDA folder (with all of its contents) and an autorun.inf file. Repeat the same process to make a portable copy (from either the installer version or the portable version). Having it named something easy to find (such as mentioned above) will make it easier to locate.

Under the preferences\tools menu, locate the create portable copy menu and press enter. On the next screen that comes up, locate the browse button. If you had made a directory beforehand on the C:\ (and called it for example portable copy for a CD), this will make it easier to find on your C:\ drive. It doesn't have to be called this, it just needs to be easy to find on the C:\ drive.  Once you have located it, create a new folder, rename it nvda, and then follow the instructions to have it install all of the contents into that folder.

The next thing you will have to do, is put the autorun.inf file into the root directory (that was created beforehand). The autorun file can be found at https://dl.dropbox.com/u/64177841/autorun.rar You will need to unzip it and move it into the directory you made earlier (for example a folder called portable copy for a CD). There should be a folder called nvda, and a file called autorun.inf  (Please note: DO NOT put the autorun.inf file into the nvda folder otherwise it will not work. Highlight both the NVDA folder and the autorun.inf file and send them to your cd/dvd burner. Follow the directions to burn them onto a CD. You will need to be familiar with your burning software to do this. Once it has been created and spits out the disk, it should just be a matter of putting the CD back into the CD/DVD burner rom. Give it a few seconds to load up, and NVDA should start talking. Once the file and folder have been burnt onto a CD, changes can not be made, so check your preferences and settings beforehand so that they are to your liking.

How to start the new NVDA package from a CD

(Please note that the autorun file for this package is different to the autorun file for making a portable copy on CD)

If you would like NVDA to start up automatically from a CD, you will need to follow these directions for it to work.
  1. Make a directory (or some people call it a folder) on your PC. Call it something easy to remember. For example, if you make the directory off the c:\ drive name it something easy to remember like... the new NVDA package CD (or whatever you want to call it).
  2. Download the latest version of NVDA (which at present is the 2012.3.1 release) and put that into the new directory you have just made. Click on it to set it up. An open file security warning should appear, giving you some information about the file (such as filename, publisher, file type etcetera). You should hear "do you want to run this file"? Untick the box that says "always ask before opening this file" and then click on Run. The next screen that comes up should be the agreement screen. Agree to the licence, tab through to install and then close it without installing anything so it remembers this setting.
  3. Download the new NVDA package autorun file from https://dl.dropbox.com/u/64177841/autorun%20nvda%20package.rar. It will need to be unrarred, so you can see the autorun.inf file and put that into your new directory (the one you made beforehand).
  4. Now you should see 2 files in the folder you have made, one being the nvda_2012.3.1 file and the other being the autorun.inf file.
  5. Highlight the 2 files, then send them to your DVD burner. Follow the onscreen directions that appear before you to the end. When the CD has been burned it should pop out of the drive (depending on how your settings are set).
  6. Put the CD back in and it should automatically start. The first screen you will see is an agreement screen, and once agreed to it will then give you 3 options: 1 to install to your PC a copy of NVDA, 2 to make a portable copy or 3 to run as a temporary copy.
If you would like to hear an audio version of making this CD, please visit the the NVDA audio tutorials page. There, you can also hear other audio tutorials on the basics of using NVDA.
The page can be found at http://homepages.slingshot.co.nz/~hurrikenny/nvda%20audio%20tutorials.html

Updating the version number of NVDA so your file can still autorun using the above package

Please note:
If you would like the autorun.inf file to work with the 2013.1 release and beyond, you will need to open the autorun.inf file with notepad and make a small change (that is you will need to change the version number) so it works in later versions. Remember to save it once changed.

For example, if you are running version 2012.3.1 and you update to 2013.1 when it comes out, where it says:
Simply change the version number... That is, change 2012.3.1 to 2013.1 and leave the rest the same!

It should now look something like this:

In this example we have only used the stable release versions.

Creating shortcuts

Hard drive shortcut
NVDA will create its own shortcut to your hard drive version of NVDA - on your computer's desktop.

Portable USB drive shortcut
The portable versions of NVDA do not automatically have a shortcut created - you will need to create these yourself. (You will need to create a shortcut to whichever folder you have unzipped the portable NVDA contents into). This may be on your hard drive (as a backup in case the hard drive version stops working for any reason), or on the USB stick itself.
Option 1 Drop a copy of the portable NVDA version onto your computer, and make a shortcut on your desktop
(Right click on your desktop... and click on new... shortcut... browse...(this will give you the option to browse for the file you want to create the shortcut for)... select the file (For example C:\NVDA\nvda.exe) and click ok... next... Type a name for this shortcut (for example nvda portable) and select finish... (this will create the shortcut). If you want to start it with a hot key, property the shortcut and assign a hot key combination that you will remember (Eg. Alt + Ctrl + P).
Option 2 Create a shortcut on the USB drive itself
Once you have extracted the files onto your USB stick, and set up NVDA, you can have a shortcut directly on the portable drive itself. To do this, use the following steps.
Put the USB drive into your USB port... click on open folder to view files... Alt (which will select your file menu)... new... shortcut... tab to browse (and select the file you want to create the shortcut for. (You will need to know the drive letter for your USB stick.) Browse to your USB drive... and go to the NVDA folder (Eg. J:\NVDA) and you are looking for the NVDA.exe file within that folder (Eg. J:\NVDA\nvda.exe). Once you have located this file, tab to ok... tab to next (to continue)...It will then ask for a name for your shortcut. (For example name it nvda or whatever you wish to call it).

The shortcut key can start with any letter, but do not have another file or folder on that stick starting with that same letter. For example, if your shortcut key is S (for start NVDA) then make sure there is no other file or folder on that stick starting with S. At the moment I use O (to open the folder) and N to start it! I like it this way because all I have have to remember is O N.

More free speech synthesisers for NVDA

NVDA comes with the E-speak voices by default, but you can also download some other voices to test them out if you would like to do so. The advantage to using the E-speak, pico and festival voices, is that they can go portable! Not all voice synthesisers can go portable on a USB stick. Please click on the links below should you wish to try some of them out.
  • Lernout & Hauspie, Microsoft, Realspeak and UkrVox voices http://www.cross-plus-a.com/balabolka.htm (This is also the website where you can download the free text to speech program called Balabolka. You can convert your text into mp3 and have it read back to you).

Using NVDA on a USB stick

Once the portable version of NVDA has been set up on your USB stick, it is simply a matter of unplugging your usb stick and plugging it back into your pc. If you have set it up previously then simply plug it in. If the autoplay menu comes up, press the letter O (to open the folder), enter,  N (for the shortcut key), and then press enter again. NVDA should just start up.  This will not work if there is no autoplay menu there, because it may be disabled for security reasons. (The autoplay menu is the menu that appears when you insert a CD rom - and it gives you options such as play, open folder to view files and so on).

Alternative way to start NVDA from a portable USB stick

There is an alternative to starting NVDA on a USB stick (instead of using a shortcut on the USB stick). It is using a batch file to start NVDA. It is easiest to start with a new USB stick, so there are no files on it. When NVDA is running, insert the USB stick and see what letter is assigned? For example e:\ Once you know, the next step is press the Escape key to make the autorun menu disappear.
Open up the preferences menu in NVDA (this is done by pressing the insert key and the letter N). Once open, arrow down to tools, where a submenu will come up, arrow down to create portable copy and press Enter. Locate the browse button, and press Enter, then locate your USB stick. For example e:\ Once there, create a new directory called nvda, press Enter and this directory should be created for you. Follow the directions to the end so the files are automatically installed into that directory. Next download the start nvda.bat file from https://dl.dropbox.com/u/64177841/start%20NVDA.rar  You will need to unrar the file so you can see a file called start nvda.bat.

Once done, copy this file to your USB stick. Make sure you don't put it into any folders, so the file should just be in the root directory. When you look at the USB stick there should be a folder called NVDA and a start nvda.bat file. Next, unplug the USB stick and then reinsert the USB stick into the computer. The autorun menu should come up. When it does, press the letter O (to open the folder), then press enter. You should then see those 2 items mentioned before (the start nvda.bat file and the nvda directory). Press the letter S to start nvda, and then press Enter and NVDA should start. The start nvda.bat file can also be renamed to nvda.bat. Instead of pressing O and then S, you could press O and then N. (The letters O and N spelling the word "on" may be easier to remember). Either way should work if set up properly.

Please note: If the autorun.inf file is used, it can only be used with a CD! If the start nvda.bat file is used, it can only be used with a USB device! Please make sure that you follow the directions for the appropriate device to ensure they work properly.

Setting your NVDA personal preferences

To get into the preferences (where you can make changes to NVDA), press the insert key and the N key. This will bring up the preferences where you can make adjustments to your liking. You will need to save your changes. This will remember it for next time. When you have finished using NVDA, press the insert key and the Q key and NVDA will be turned off.

Background information

When you download a major release of NVDA from the downloads section, it is what they call a stable release.  These will have a signed certificate name for example 2013.2, and they are the stable releases that the public will use.

In between these stable releases, are experimental releases called development snapshots. Think of a camera taking pictures of a building being built. Each snapshot shows a stage of development of the building process. The NVDA snapshots show a stage by stage time-line of the screen reader's development on a particular day.  These are done (usually daily) and uploaded nightly to the server.  These snapshots are what is called "experimental code".  They are usually quite stable, but at times can be quite buggy, or may not even work at times.  They are for trying out new ideas, bug fixing and so on. They are like your alpha and beta releases of software.  These are usually used for testing purposes. As the code improves, it will go from alpha to beta (at snapshot stage) and to a release candidate (just before the official stable release stage). To get a better idea of what has been done in each snapshot, if you look under the time-line link, it will tell you what has been done for that day.  There may have been new tickets made (for errors that were found) or old tickets closed (for errors that were fixed). It varies from day to day.

People usually ask when the next release of NVDA will be.  From past history, it is usually quarterly (around Feb 23rd, May 23rd, Aug 23rd and Nov 23rd of each year) if the release process goes well. It depends what comes up before the release. This information is put onto the main NVDA homepage - letting people know what stage they are up to before the final release. (The beta release, release candidate and stable version are all advertised on the homepage before the official release).

Once all of the tickets have been done, and reached 100 percent, then they will do the beta releases, then the release candidate, then the stable release which the public will use. (For example when all the tickets for 2013.1 are completed, then work begins on the 2013.2 release and so on). The beta and release candidates must be stable as well.

When an official major release is made of a version of NVDA, the process starts all over again, and the next version's features and improvements are worked on. As with any successful computer programme, development is essential to ensure it works with newer programmes on the market, and it is a matter of continuous feedback and development.

Click on the following link to discover more in-depth information about NVDA development for the release process.  http://www.nvda-project.org/wiki/ReleaseProcess

Joining the NVDA Community

The following are some shortcut keys and tips to help you get started with NVDA

If you are running the hard drive version on your desktop:
  • Alt + Ctrl + N will start up NVDA.
  • Insert + N ... preferences will take you into a menu where you can make changes to your liking such as: voice settings, document formatting and so on.
  • Insert + N ... help will take you into your help section where you will find things such as the user guide, a keyboard command quick reference and a what's new segment.
  • Insert + N ... save configuration... will save the settings that you have just changed in your NVDA.
  • Insert + Q ... closes the programme.
If you are running NVDA on a laptop, you may need to set the keyboard settings to that by doing the following:
  • Insert + N...preferences...keyboard settings... (and using the drop down box) select laptop. Some netbooks do not have a full 101 qwerty keyboard and need to be set to laptop rather than desktop. If however you add a USB keyboard to your netbook then you can change the setting back to desktop. This really depends on how you enter text into your computer.
Regardless of whether you are using NVDA on a desktop or laptop, it is helpful to read the help files first which will make screen reader navigation much faster.

If the computer you are going to use, doesn't come up with the autorun dialog, when your CD or USB stick is inserted, you can do the following to make it load.

Press the Windows key and the letter R to bring up the run dialog.  Type in (as an example, if the letter has been assigned to e: drive)  e:\nvda\nvda.exe then press the Enter key, and NVDA will start.  If it doesn't, another letter may have been assigned to it.  The path will still be the same apart from the drive letter assigned.  For example J:\nvda.nvda.exe