[FFmpeg-devel] [PATCH 1/2] libx264: remove the "x264opts" AVOption

Jan Ekstrom jeebjp at gmail.com
Wed Mar 8 01:41:38 EET 2017

On Wed, Mar 8, 2017 at 1:01 AM, Michael Niedermayer
<michael at niedermayer.cc> wrote:
> the fast pskip i mentioned yesterday
> ./ffmpeg -y -i ~/videos/matrixbench_mpeg2.mpg -vcodec libx264 -x264-params fast-pskip -vframes 15 -an ref-p.nut
> ./ffmpeg -y -i ~/videos/matrixbench_mpeg2.mpg -vcodec libx264 -x264-params no-fast-pskip -vframes 15 -an ref-np.nut
> ./ffmpeg -y -i ~/videos/matrixbench_mpeg2.mpg -vcodec libx264 -x264opts no-fast-pskip -vframes 15 -an ref-no.nut
> ./ffmpeg -y -i ~/videos/matrixbench_mpeg2.mpg -vcodec libx264 -x264opts fast-pskip -vframes 15 -an ref-o.nut
> ffd2c735cfb268d5f4291c2f6baab386  ref-o.nut
> ffd2c735cfb268d5f4291c2f6baab386  ref-p.nut
> f424075a964018aa83f98f2bf5ab2830  ref-no.nut
> ffd2c735cfb268d5f4291c2f6baab386  ref-np.nu
> it appears *fast-pskip has no effect in x264-params

Right, as I noted in my previous message, the custom dictionary
parsing code in there sets the value to "1" if a value is not
available. The API always expects a key and a value (even if a NULL
value would be valid for a boolean option).
So to emulate what x264opts is doing you would just set "fast-pskip=1"
or "no-fast-pskip=1". You can by this guess that fast-pskip is indeed
the default behavior during medium preset in libx264.

In my personal opinion I'm not sure this is worth it to have a Yet
Another Dictionary Parser inside libx264.c, esp. since
av_dict_parse_string() behavior is already the defining one in
multiple components where key/value lists are handled (you can see our
Doxygen for some sort of list of usage:

> i have no idea if thats the only issue

Unless the very short code around it, or av_dict_parse_string is
globally bugged in some way, most likely all "issues" with x264-params
are due to the implicit value being set for key-value pairs without a

> also to keep both x264-params and x264opts working you need just
> 1 line more than if you drop one. Its just one entry in the AVOption
> array to pass both to the same implementation

That is another alternative and at the very least would remove the
duplicated implementation which would be a positive step forward. For
some reason I would prefer only having a single option for this so
that there would be no questions regarding why the behavior changed
for x264opts with regards to implicit values.

Best regards,
Jan Ekström

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