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

[Fu, Linjie]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of
> Nicolas George
> Sent: Saturday, February 15, 2020 19:01
> To: FFmpeg development discussions and patches <ffmpeg-
> devel at ffmpeg.org>
> Cc: Fu, Linjie <linjie.fu at intel.com>; Eoff, Ullysses A
> <ullysses.a.eoff at intel.com>
> Subject: Re: [FFmpeg-devel] [PATCH] fftools/ffmpeg_filter: add -autoscale
> to disable/enable the default scale
> 
> Linjie Fu (12020-02-15):
> > Currently, ffmpeg inserts scale filter by default in the filter graph
> > to force the whole decoded stream to scale into the same size with the
> > first frame. It's not quite make sense in resolution changing cases if
> > user wants the rawvideo without any scale.
> >
> > Using autoscale/noautoscale as an output option to indicate whether auto
> > inserting the scale filter in the filter graph:
> >     -noautoscale or -autoscale 0:
> >     disable the default auto scale filter inserting.
> >
> > ffmpeg -y input.mp4 out1.yuv -noautoscale out2.yuv -autoscale 0 out3.yuv
> >
> > Update docs.
> >
> > Signed-off-by: U. Artie Eoff <ullysses.a.eoff at intel.com>
> > Signed-off-by: Linjie Fu <linjie.fu at intel.com>
> > ---
> >
> > Using autoscale as an output option and fix the missing spaces.
> >
> >  doc/ffmpeg.texi         | 16 ++++++++++++----
> >  fftools/ffmpeg.h        |  3 +++
> >  fftools/ffmpeg_filter.c |  2 +-
> >  fftools/ffmpeg_opt.c    |  8 ++++++++
> >  4 files changed, 24 insertions(+), 5 deletions(-)
> >
> > diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
> > index 29753f0..aebafb3 100644
> > --- a/doc/ffmpeg.texi
> > +++ b/doc/ffmpeg.texi
> > @@ -734,10 +734,6 @@ ffmpeg -dump_attachment:t "" -i INPUT
> >  Technical note -- attachments are implemented as codec extradata, so this
> >  option can actually be used to extract extradata from any stream, not just
> >  attachments.
> > -
> > - at item -noautorotate
> > -Disable automatically rotating video based on file metadata.
> > -
> >  @end table
> >
> >  @section Video Options
> > @@ -819,6 +815,18 @@ Create the filtergraph specified by
> @var{filtergraph} and use it to
> >  filter the stream.
> >
> >  This is an alias for @code{-filter:v}, see the @ref{filter_option,,-filter
> option}.
> > +
> > + at item -autorotate
> > +Automatically rotate the video according to file metadata. Enabled by
> > +default, use @option{-noautorotate} to disable it.
> > +
> > + 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 of filter graph might not be in the same
> resolution
> > +and may be inadequate for some encoder/muxer. Therefore, it is not
> recommended
> > +to disable it unless you really know what you are doing.
> > +Disable autoscale at your own risk.
> >  @end table
> >
> >  @section Advanced Video options
> > diff --git a/fftools/ffmpeg.h b/fftools/ffmpeg.h
> > index 7b6f802..8beba6c 100644
> > --- a/fftools/ffmpeg.h
> > +++ b/fftools/ffmpeg.h
> > @@ -230,6 +230,8 @@ typedef struct OptionsContext {
> >      int        nb_time_bases;
> >      SpecifierOpt *enc_time_bases;
> >      int        nb_enc_time_bases;
> > +    SpecifierOpt *autoscale;
> > +    int        nb_autoscale;
> >  } OptionsContext;
> >
> >  typedef struct InputFilter {
> > @@ -479,6 +481,7 @@ typedef struct OutputStream {
> >      int force_fps;
> >      int top_field_first;
> >      int rotate_overridden;
> > +    int autoscale;
> >      double rotate_override_value;
> >
> >      AVRational frame_aspect_ratio;
> > diff --git a/fftools/ffmpeg_filter.c b/fftools/ffmpeg_filter.c
> > index 40cc4c1..46c8ea8 100644
> > --- a/fftools/ffmpeg_filter.c
> > +++ b/fftools/ffmpeg_filter.c
> > @@ -469,7 +469,7 @@ static int configure_output_video_filter(FilterGraph
> *fg, OutputFilter *ofilter,
> >      if (ret < 0)
> >          return ret;
> >
> > -    if (ofilter->width || ofilter->height) {
> > +    if ((ofilter->width || ofilter->height) && ofilter->ost->autoscale) {
> >          char args[255];
> >          AVFilterContext *filter;
> >          AVDictionaryEntry *e = NULL;
> > diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
> > index 12d4488..62bcfc1 100644
> > --- a/fftools/ffmpeg_opt.c
> > +++ b/fftools/ffmpeg_opt.c
> > @@ -1405,6 +1405,8 @@ static OutputStream
> *new_output_stream(OptionsContext *o, AVFormatContext *oc, e
> >          ost->encoder_opts  = filter_codec_opts(o->g->codec_opts, ost->enc-
> >id, oc, st, ost->enc);
> >
> >          MATCH_PER_STREAM_OPT(presets, str, preset, oc, st);
> > +        ost->autoscale = 1;
> > +        MATCH_PER_STREAM_OPT(autoscale, i, ost->autoscale, oc, st);
> >          if (preset && (!(ret = get_preset_file_2(preset, ost->enc->name, &s))))
> {
> >              do  {
> >                  buf = get_line(s);
> > @@ -3650,6 +3652,12 @@ 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_OUTPUT,                               { .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."},
> 
> The help text for most options is half a line. This one is four long
> lines. Maybe this is misusing the field: a short summary here, the full
> explanation in the doc.

How about shortening into
"automatically insert a scale filter at the end of the filter graph if a resolution change is detected (enabled by default)."
in the help message and keep the current explanation unchanged in doc?

> Regards,
> 
> --
>   Nicolas George

Thanks for pointing this out.