[FFmpeg-devel] [PATCH, v3] fftools/ffmpeg_filter: add -autoscale to disable/enable the default scale

[Fu, Linjie]

> -----Original Message-----
> From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf
> Of Paul B Mahol
> Sent: Wednesday, July 24, 2019 21:17
> To: FFmpeg development discussions and patches <ffmpeg-
> devel at ffmpeg.org>
> Subject: Re: [FFmpeg-devel] [PATCH, v3] fftools/ffmpeg_filter: add -
> autoscale to disable/enable the default scale
> 
> On 7/24/19, Fu, Linjie <linjie.fu at intel.com> wrote:
> >> -----Original Message-----
> >> From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On
> Behalf
> >> Of Paul B Mahol
> >> Sent: Wednesday, July 24, 2019 17:42
> >> To: FFmpeg development discussions and patches <ffmpeg-
> >> devel at ffmpeg.org>
> >> Subject: Re: [FFmpeg-devel] [PATCH, v3] fftools/ffmpeg_filter: add -
> >> autoscale to disable/enable the default scale
> >>
> >> On 7/24/19, Fu, Linjie <linjie.fu at intel.com> wrote:
> >> >> -----Original Message-----
> >> >> From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On
> >> Behalf
> >> >> Of Gyan
> >> >> Sent: Wednesday, July 24, 2019 12:28
> >> >> To: ffmpeg-devel at ffmpeg.org
> >> >> Subject: Re: [FFmpeg-devel] [PATCH, v3] fftools/ffmpeg_filter: add -
> >> >> autoscale to disable/enable the default scale
> >> >>
> >> >>
> >> >>
> >> >> On 24-07-2019 08:15 AM, Fu, Linjie wrote:
> >> >> >> -----Original Message-----
> >> >> >> From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org]
> On
> >> >> Behalf
> >> >> >> Of Gyan
> >> >> >> Sent: Wednesday, July 24, 2019 00:49
> >> >> >> To: ffmpeg-devel at ffmpeg.org
> >> >> >> Subject: Re: [FFmpeg-devel] [PATCH, v3] fftools/ffmpeg_filter: add
> >> >> >> -
> >> >> >> autoscale to disable/enable the default scale
> >> >> >>
> >> >> >>
> >> >> >>
> >> >> >> On 22-07-2019 01:40 PM, Fu, Linjie wrote:
> >> >> >>>> -----Original Message-----
> >> >> >>>> From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org]
> >> On
> >> >> >> Behalf
> >> >> >>>> Of Gyan
> >> >> >>>> Sent: Saturday, July 20, 2019 13:29
> >> >> >>>> To: ffmpeg-devel at ffmpeg.org
> >> >> >>>> Subject: Re: [FFmpeg-devel] [PATCH, v3] fftools/ffmpeg_filter:
> >> >> >>>> add
> >> -
> >> >> >>>> autoscale to disable/enable the default scale
> >> >> >>>>> diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
> >> >> >>>>> index cd35eb49c8..99121b6981 100644
> >> >> >>>>> --- a/doc/ffmpeg.texi
> >> >> >>>>> +++ b/doc/ffmpeg.texi
> >> >> >>>>> + at item -autoscale
> >> >> >>>>> +Automatically scale the video according to the resolution of
> >> >> >>>>> first
> >> >> frame.
> >> >> >>>>> +Enabled by default, use @option{-noautoscale} to disable it.
> >> When
> >> >> >>>> autoscale is
> >> >> >>>>> +disabled, all output frames might not be in the same
> resolution
> >> >> >>>>> and
> >> >> >> may
> >> >> >>>> require
> >> >> >>>>> +some additional explicit processing according to your final
> >> >> >>>> rendering/output
> >> >> >>>>> +destination. Disabling autoscale may not work in all
> >> >> >>>>> situations.
> >> >> >> Therefore,
> >> >> >>>> it
> >> >> >>>>> +is not recommended to disable it unless you really know what
> >> you
> >> >> are
> >> >> >>>> doing.
> >> >> >>>>> +Disable autoscale at your own risk.
> >> >> >>>> Since the auto scaling happens at the end of the graph, what may
> >> the
> >> >> >>>> "additional explicit processing" be?
> >> >> >>> Vpp processing may not be influenced,  a warning in transcode is
> >> >> >>> needed.
> >> >> >>> The expression seems to be improper, how about:
> >> >> >>>
> >> >> >>> "When autoscale is disabled, all output frames of filter graph
> >> >> >>> might
> >> >> >>> not
> >> >> be
> >> >> >> in the same
> >> >> >>> resolution and may be inadequate for encoder/muxer."
> >> >> >>>
> >> >> >>> or other suggestions?
> >> >> >>>
> >> >> >>>>> @@ -3640,6 +3642,12 @@ const OptionDef options[] = {
> >> >> >>>>>         { "autorotate",       HAS_ARG | OPT_BOOL | OPT_SPEC |
> >> >> >>>>>                               OPT_EXPERT | OPT_INPUT,
> >> >> >>>>>                 { .off =
> >> >> >>>> OFFSET(autorotate) },
> >> >> >>>>>             "automatically insert correct rotate filters" },
> >> >> >>>>> +    { "autoscale",        HAS_ARG | OPT_BOOL | OPT_SPEC |
> >> >> >>>>> +                          OPT_EXPERT | OPT_INPUT,
> >> >> >>>>>              { .off =
> >> >> >>>> OFFSET(autoscale) },
> >> >> >>>>> +        "automatically insert a scale filter at the end of the
> >> >> >>>>> filter graph if
> >> >> a
> >> >> >>>> resolution"
> >> >> >>>>> +        "change is detected. This ensures all frames are the
> >> >> >>>>> same
> >> >> >> resolution
> >> >> >>>> as the first frame"
> >> >> >>>>> +        "when they leave the filter chain (this option is
> >> >> >>>>> enabled
> >> >> >>>>> by
> >> >> >> default)."
> >> >> >>>>> +        "If disabled, some encoders/muxers may not support this
> >> >> mode."},
> >> >> >>>> Which muxers can detect or check for prop changes within coded
> >> >> >>>> bitstreams? Which encoders are known to be able to handle
> >> >> >>>> changing resolution?
> >> >> >>> It's not supported currently (even in libvpx-vp9, since vp9
> >> >> >>> supports
> >> >> >> dynamic resolution in spec).
> >> >> >>> I don't intend to be so absolutely in doc,  will it be better for
> >> >> >>> you
> >> >> >>> to
> >> >> modify
> >> >> >> like:
> >> >> >>> "If disabled, encoders/muxers won't support this mode
> currently."
> >> >> >> So other than    `-c:v rawvideo -f rawvideo`, there is no
> >> >> >> combination
> >> >> >> that supports changing frame sizes?
> >> >> > I didn't check all encoders.
> >> >> > But since the resolution changing is detectable, some additional
> >> >> > reinit
> >> >> procedures
> >> >> > can be added to change resolution at IDR frame and make the
> encoder
> >> >> works.
> >> >> >
> >> >> They could, but as of now, which encoder + muxer combinations are
> >> >> **known** to work?
> >> >>
> >> > As far as I tried, no.
> >> > (pipeline failed in libx264,  garbage exists in libx265 and libvpx-vp9
> >> > )
> >>
> >> Than how this change can be useful to us?
> >>
> >> It will just increase maintenance burden on other developers.
> >
> > Why?
> > This option does no harm to current filter graph since auto scale is enabled
> > by default,
> > and won't be disabled only if user really knows what he is doing.
> >
> > It could be used  for raw video dump currently, and provided the possibility
> > for dynamic
> > Resolution encoding as well.
> >
> 
> It is incomplete functionality at best.

Provided a patch to support dynamic resolution encode for libvpx-vp9.
Thus "noautoscale" option makes more sense in transcode.
Please help to review.

- linjie