The set bitrate is not respected when kVTCompressionPropertyKey_AverageBitRate is used. constant and variable bitrates seems to work, only average that is broken. All three modes works in iOS 26.
kVTCompressionPropertyKey_AverageBitRate seems to be broken in iOS 27 Beta
Thank you for reporting this issue. Could you provide more details about what you’re experiencing and clarify what you mean by kVTCompressionPropertyKey_AverageBitRate being broken?
Please also file a Feedback Assistant report at https://developer.apple.com/feedback-assistant/ and, if possible, attach a sample project and the video content that reproduces the issue. Once the report has been submitted, please share the FBA number here so we can help ensure it is routed promptly to the appropriate team.
I submitted using the Feedback app a few days ago, but it seems you guys at Apple never respond to those. I have submitted three, and none has been addressed.
I'll not submit more details as it taks lots of effort, and I doubt you'll look at it, sorry.
Here is my project: https://github.com/eerimoq/moblin
In the project above, the abr mode sets both kVTCompressionPropertyKey_AverageBitRate and kVTCompressionPropertyKey_DataRateLimits, with the data rate limit configured to be higher than the average bitrate (i.e. 1.2x).
When you mention that the behavior is broken in iOS 27, do you mean that the resulting average bitrate differs from the value specified by kVTCompressionPropertyKey_AverageBitRate, or the instant bitrate is above kVTCompressionPropertyKey_DataRateLimits, or something else?
What are the differences have you noticed in this behavior between OS 26 and OS 27 with your video content?
In addition, since you’ve already submitted reports through Feedback Assistant, could you please share the report links here? Thanks
Yeah the average is lower than configured in kVTCompressionPropertyKey_AverageBitRate. Typically the app changes the target bit rate quite frequently to adapt to cellular network conditions, which may have some significance to the problem. I tried increasing the data rate limits, but didn't seem to help.
On iOS 26 and older, the encoder outputs data at configured target bit rate.
Feedback ID: FB23692301
There is also a discussion at discord: https://discord.com/channels/1146357402250260580/1517450179282731008
Discord invite link: https://discord.gg/kh3KMng4JV