# Meaning of \_definst\_ in links to media files
**URL:** https://community.wowza.com/t/meaning-of-definst-in-links-to-media-files/45350
**Category:** Wowza Streaming Engine
**Created:** [August 12, 2015, 12:18pm UTC](https://community.wowza.com/t/meaning-of-definst-in-links-to-media-files/45350 "2015-08-12T12:18:30Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Anton\_Tremetzberger](https://community.wowza.com/u/Anton_Tremetzberger)
#### Post date: [August 12, 2015, 12:18pm UTC](https://community.wowza.com/t/meaning-of-definst-in-links-to-media-files/45350/1 "2015-08-12T12:18:30Z")
Dear wowza community,
I am not shure about the meaning of the “_definst_” in links to media files and I hope you can help me:
I set up a video on demand application called “vod”. If I open a media file, e.g:
```auto
rtmp://[wowza-ip-address]:1935/vod/_definst_/mp4:subfolder/subsubfolder/sample.mp4
```
the file will be played.
If I change the link to e.g.:
```auto
rtmp://[wowza-ip-address]:1935/vod/video123/mp4:subfolder/subsubfolder/sample.mp4
```
the file will also be played. If I remove “_definst_”, the file will not be played, e.g.:
```auto
rtmp://[wowza-ip-address]:1935/vod/mp4:subfolder/subsubfolder/sample.mp4
```
My questions are:
What happens if I use “video123”, “audio123” or any other string instead of "_definst_? Is there any side effect (eg video could not be played in some players or on some devices?) Are there any limitations to the name of the string?
Is der any possibility to remove “_definst_”?
So, the link will be
```auto
rtmp://[wowza-ip-address]:1935/vod/mp4:subfolder/subsubfolder/sample.mp4
```
thank you & best regards,
Anton
---
### Author:  [@sal\_jefferson](https://community.wowza.com/u/sal_jefferson)
#### Post date: [August 12, 2015, 6:32am UTC](https://community.wowza.com/t/meaning-of-definst-in-links-to-media-files/45350/2 "2015-08-12T06:32:54Z")
Hello Anton.
> An Application.xml file defines the configuration that you set up in Wowza Streaming Engine Manager for a given application. An application instance is an instantiation of an application and provides a namespace and context for streaming. An application instance is started dynamically and a single application can have multiple named application instances running simultaneously. If no name is specified for an application instance, then the default name (_definst_) is used. In many streaming scenarios, a single application instance is used per- application and the name is never referenced and defaults to _definst_. It’s more common to use multiple application instances in video chat and video conferencing scenarios where you must create multiple rooms for streaming. In this case, application instances are used to separate streaming into rooms. Each room is a separate application instance, which provides separation and a namespace for each room.
You define application instances in the playback URL like you have done in this example:
```auto
rtmp://[wowza-ip-address]:1935/vod/video123/mp4:subfolder/subsubfolder/sample.mp4
```
You can also define the application instance when publishing a live stream:
```auto
rtmp://[wowza-address]:1935/live/instance1/myStream
```
You don’t create application instances anywhere else in configuration files.
When using a subfolder for content, or a folder other then the /content folder, you will need to name an application instance, or use _definst_ to access the files.
I hope this answers your question.
Regards,
Salvadore
---
### Author:  [@sal\_jefferson](https://community.wowza.com/u/sal_jefferson)
#### Post date: [August 13, 2015, 5:11am UTC](https://community.wowza.com/t/meaning-of-definst-in-links-to-media-files/45350/3 "2015-08-13T05:11:59Z")
Anton, you are most welcome. I am glad I could help.
I did update my response however.
> When using a subfolder for content, or a folder other then the /content folder, you will need to name an application instance, or use _definst_ to access the files.
>
> Regards,
>
> Salvadore
---
### Author:  [@Anton\_Tremetzberger](https://community.wowza.com/u/Anton_Tremetzberger)
#### Post date: [August 13, 2015, 10:16am UTC](https://community.wowza.com/t/meaning-of-definst-in-links-to-media-files/45350/4 "2015-08-13T10:16:30Z")
Dear Salvadore,
now I understand, thanks for your help and explaining.
best regards, Anton