How to set the H.264 GOP length in x264enc?

[Jan Alexander Steffens]

On Wed, Mar 28, 2018 at 12:12 AM Andres Gonzalez <andres.agoralabs at gmail.com>
wrote:

> Hi,
>
> I have been tasked to test some decoders regarding how they respond to
> different streams with various  GOP lengths (GOP length is the ratio of
> Intracoded-to-Predictive or I-to-P frames). I am using several pipelines
> with the x264enc plugin and all seems to be working fine. But in reviewing
> the properties for x264enc, it is not clear to me how to configure x264enc
> so I can nail it down for various GOP lengths. There are a lot of
> properties
> related to B frames but not too many for I/P frames.
>
> Two x264enc properties:
> ip-factor: Quantizer factor between I- and P- frames     This appears to
> relate to quantizing and not a ratio; plus it is only in the range of 0-2
>
> key-int-max: Maximal distance between two key-frames     Again, only deals
> with the frequency of I frames regardless of what kind of frames come
> between them.
>
> So, how can I configure x264enc for various GOP lengths like 1, 15, or 30?
>
> Thanks,
> -Andres
>

If you disable scene detection using option-string="scenecut=0",
key-int-max will be your I frame interval. So for a I-to-P+B ratio of 1:15,
set key-int-max=16.
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