[FFmpeg-devel] [PATCH] examples: set GOP size to 10 seconds

[Michael Niedermayer]

On Tue, Oct 29, 2019 at 10:25:03AM +0100, Alfred E. Heggestad wrote:
> using a gop_size of 10 in the example code is very misleading.
> in practice this means around 2 keyframes per second.
> 
> a normal video encoder should not send keyframes so frequent,
> a better interval is 10 seconds.
> 
> Signed-off-by: Alfred E. Heggestad <alfred.heggestad at gmail.com>
> ---
>  doc/examples/encode_video.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/doc/examples/encode_video.c b/doc/examples/encode_video.c
> index d9ab409908..8c5ee9818e 100644
> --- a/doc/examples/encode_video.c
> +++ b/doc/examples/encode_video.c
> @@ -110,13 +110,13 @@ int main(int argc, char **argv)
>      c->time_base = (AVRational){1, 25};
>      c->framerate = (AVRational){25, 1};
> 
> -    /* emit one intra frame every ten frames
> +    /* emit one intra frame every ten seconds
>       * check frame pict_type before passing frame
>       * to encoder, if frame->pict_type is AV_PICTURE_TYPE_I
>       * then gop_size is ignored and the output of encoder
>       * will always be I frame irrespective to gop_size
>       */
> -    c->gop_size = 10;
> +    c->gop_size = 10 * 25;

several codecs have a limit of 132 dependant non key blocks
so 250 is a risky default, it would only strictly be valid with B frames
for some codecs
I know 10sec is commonly used but i think it should not be the recommanded
default in an example for the reason above. Especially not without
clear documentation of the spec violation this could cause

Thanks

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Everything should be made as simple as possible, but not simpler.
-- Albert Einstein
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