[x264-devel] question regading encoded keyframe size at 720p

[Carl Petersen]

Hi Henrik,

Yes. Vbv buffer size is 2000 and vbv max_rate is 1024. About a year ago
buffer size was 350 and it was increased to 2000. I have a basic
understanding of how vbv works but I still can't grasp on what values to
choose for our application. 350 was too low. There were frequent artifacts
that seemed to correspond to keyframes. Increasing it to 2000 alleviated the
problem but I still cant fully comprehend the impact of that. I can sort of
appreciate that it can increase keyframe size. What I don’t understand is
why 350 was too low. Was that vbv overflow? And I don’t know what value to
pick for vbv buffer size.



-----Original Message-----
From: x264-devel [mailto:x264-devel-bounces at videolan.org] On Behalf Of
Henrik Gramner
Sent: Wednesday, October 14, 2015 4:35 PM
To: Mailing list for x264 developers
Subject: Re: [x264-devel] question regading encoded keyframe size at 720p

On Wed, Oct 14, 2015 at 10:27 PM, Carl Petersen <cpetersen at broadsoft.com>
wrote:
> It’s a video conferencing application and the resolution is 1280x720.
>
> We set CRF to 24 and aim for a bitrate of 1024 kbit/s.
>
> Ive noticed the keyframe sizes can be well over 100 kbytes or well over
> 100 rtp packets when packetized. We don’t do intra refresh at this point
> in time.
>
> Though when I compare this keyframe size  with other devices, the other
> devices appear to have a much smaller keyframe size at a similar bitrate.
>
> What do I need to consider if I wanted to reduce the keyframe size? Are
> the other devices just encoding at a lower quality? But then I see their
> bitrate is similar to mine so I must be missing a part of the bigger
> picture.
>
> Baseline profile.

Hi,

Are you using VBV?
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