Add ABR support

[bsriramprasad]

Feature background/motivation

• IP video surveillance needs to balance video quality with predictable storage and bandwidth. Currently ONVIF Media2 service specification only supports Constant bitrate and Maximum bitrate parameters
• Average bitrate feature, if standardized/configured from ONVIF, devices can try and adapt output bitrate internally to provide target bitrate over time, allowing higher instantaneous bitrates for complex scenes while not exceeding an overall target average.

Spec proposal

• Extended video rate control structure tt:VideoRateControl2 with 2 parameters
  • AverageBitRate (feature toggle)
  • TargetAverageBitrate (target bitrate devices should adapt output to meet the client storage targets)
• Extended tt:VideoEncoder2ConfigurationOptions with below parameter
  • AverageBitRateSupported (capability flag)

[bsriramprasad]

@bsriramprasad is there not a need to update the Meda2 Specification to reflect these new changes for ABR?

@kieran242 Good question, I looked into the Media2 spec and I did not see any earlier reference where let's say constant bit rate (CBR) related features are explained to be complemented with the current feature in discussion 'ABR'.

The only requirement I could see is the below

A device shall adapt an out of range BitrateLimit instead of returning a fault.

Having said that, I am open to feedback from Montreal meetings and see how it can be added.