On Tue, Apr 2, 2019 at 4:16 PM Peter Gusev <gpee...@gmail.com
> Wanted to check in with the community on the expected encoder behavior.
> I have a 1280x720 video which I encode at 30fps, GOP 30, 3000 bitrate. (see attached source code for the full encoder setup).
> I then collect 1000 individual encoded frame sizes in bytes and plot them (alongside GOP number to see when new Key frame was generated).
> From the data I collect, calculated bitrate is about 1000.
> And the plot (see attached) shows occasional spikes in frame sizes (I'd expect Key frames be these spikes, but surprisingly, this is not the case).
Can you include the command line you used to generate the content?
> I'm not a video encoder expert, thus I would like to check in with more experienced folks on the following:
> -- should the resulted bitrate (~1K) be of a concern? why encoder does not target for specified (3K) bitrate?
That can depend on the content and the encoder settings used. The
encoder may undershoot on easier material or if the chosen bitrate is
overly high for the resolution.
> -- is there any way to force encoder not to generate "spikes", i.e. keep frame sizes relatively the same? from the encoder setup source file you can see I use rc_undershoot_pct and rc_overshoot_pct, but it doesn't seem to be helping.
You can further control key frame sizes with the max-intra-rate 
option for vp8/9, vp9 also allows tuning on inter .
> -- is there any way to predict when encoder is about to generate a "spike"?
In general the encoder will spend more bits on key frames, golden
frames and alternate reference frames (controlled by --lag-in-frames,
but it's a range rather than a forced distance).
> Peter Gusev
> +1 213 587-27-48
> Research Scholar @ REMAP UCLA
> Video streaming/ICN networks/Creative Coding/Interactive Media
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