Affected Roles: System Owner • System Administrator
Related Nx VMS Apps: Nx Media Server
What is transcoding and why is there a limit on simultaneous sessions?
Transcoding is the process of taking compressed or encoded content, decompressing or decoding it, and then modifying it in some way and re-compressing or re-encoding it. The most common scenario is decreasing the resolution and bitrate/framerate. Sometimes this can include changing a video or audio format from one to another (e.g, MJPEG to H264), or adding watermarks to the video.
A transcoding session is one instance of this process, so when you need to transcode multiple things you can have multiple sessions in order to transcode simultaneously. This session is initated when the GET/media/<cameraId>.<format> api call is made with webm and mpjpeg in format and links with a custom resolution parameter.
In Nx Witness 4.0, we set a default limit of no more than 2 simultaneous transcoding sessions. This limit was put in place to avoid CPU overload issues that were often observed at sites with progressive download enabled. As a result, this change may break some integrations which relied on more than 2 simultaneous transcoding sessions.
How to increase the number of simultaneous transcoding sessions?
- Administrator level permissions are required to make the change.
- Modify the following address and enter it into your browser:
- To increase this limit, on the advanced settings page search for:
Max amount of WEBM connections for the server. Chrome opens 2 connections at once, then close the first one. So, it is recommended to set value >=2 to this parameter.
- Modify the value of the maxWebMTranscoders parameter.
- Click Save to confirm your changes.
- Restart the server.
Please be aware of the potential CPU overload. We don't recommend increasing this value unless your hardware is suitable for the task.