[FFmpeg-devel,3/3] libavfilter/graphparser: Add scale_sws_opts parse support in avfilter_graph_parse2

From: Linjie Fu <linjie.justin.fu@gmail.com>

To pass the swscale options for the inserted scalers.

ffmpeg -i input.mp4 -filter_complex \
    "scale_sws_opts=alphablend=checkerboard;format=nv12" \
    -t 0.5 output.mp4

Update docs.

Signed-off-by: Linjie Fu <linjie.justin.fu@gmail.com>
---
 doc/filters.texi          |  7 ++++---
 libavfilter/graphparser.c | 27 +++++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 3 deletions(-)

Linjie Fu:
> From: Linjie Fu <linjie.justin.fu@gmail.com>
> 
> To pass the swscale options for the inserted scalers.
> 
> ffmpeg -i input.mp4 -filter_complex \
>     "scale_sws_opts=alphablend=checkerboard;format=nv12" \
>     -t 0.5 output.mp4
> 
> Update docs.
> 
> Signed-off-by: Linjie Fu <linjie.justin.fu@gmail.com>
> ---
>  doc/filters.texi          |  7 ++++---
>  libavfilter/graphparser.c | 27 +++++++++++++++++++++++++++
>  2 files changed, 31 insertions(+), 3 deletions(-)
> 
> diff --git a/doc/filters.texi b/doc/filters.texi
> index 790d165433..dbbb3a6940 100644
> --- a/doc/filters.texi
> +++ b/doc/filters.texi
> @@ -204,9 +204,9 @@ pads must be connected. A filtergraph is considered valid if all the
>  filter input and output pads of all the filterchains are connected.
>  
>  Libavfilter will automatically insert @ref{scale} filters where format
> -conversion is required. It is possible to specify swscale flags
> -for those automatically inserted scalers by prepending
> -@code{sws_flags=@var{flags};}
> +conversion is required. It is possible to specify swscale flags or
> +scale_sws_opts for those automatically inserted scalers by prepending
> +@code{sws_flags=@var{flags};} or @code{scale_sws_opts=@var{scale_sws_opts};}
>  to the filtergraph description.
>  
>  Here is a BNF description of the filtergraph syntax:
> @@ -219,6 +219,7 @@ Here is a BNF description of the filtergraph syntax:
>  @var{FILTER}           ::= [@var{LINKLABELS}] @var{FILTER_NAME} ["=" @var{FILTER_ARGUMENTS}] [@var{LINKLABELS}]
>  @var{FILTERCHAIN}      ::= @var{FILTER} [,@var{FILTERCHAIN}]
>  @var{FILTERGRAPH}      ::= [sws_flags=@var{flags};] @var{FILTERCHAIN} [;@var{FILTERGRAPH}]
> +@var{FILTERGRAPH}      ::= [scale_sws_opts=@var{opts};] @var{FILTERCHAIN} [;@var{FILTERGRAPH}]
>  @end example
>  
>  @anchor{filtergraph escaping}
> diff --git a/libavfilter/graphparser.c b/libavfilter/graphparser.c
> index 1385c3ae71..8c63d6454e 100644
> --- a/libavfilter/graphparser.c
> +++ b/libavfilter/graphparser.c
> @@ -415,6 +415,30 @@ static int parse_sws_flags(const char **buf, AVFilterGraph *graph)
>      return 0;
>  }
>  
> +static int parse_scale_sws_opts(const char **buf, AVFilterGraph *graph)
> +{
> +    char *p = strchr(*buf, ';');
> +
> +    if (strncmp(*buf, "scale_sws_opts=", 15)) {

av_strstart()

> +        return 0;
> +    }
> +
> +    if (!p) {
> +        av_log(graph, AV_LOG_ERROR, "scale_sws_opts not terminated with ';'.\n");
> +        return AVERROR(EINVAL);
> +    }
> +
> +    *buf += 15;
> +
> +    av_freep(&graph->scale_sws_opts);
> +    if (!(graph->scale_sws_opts = av_mallocz(p - *buf + 1)))
> +        return AVERROR(ENOMEM);
> +    av_strlcpy(graph->scale_sws_opts, *buf, p - *buf + 1);

av_strndup()

> +
> +    *buf = p + 1;
> +    return 0;
> +}
> +
>  int avfilter_graph_parse2(AVFilterGraph *graph, const char *filters,
>                            AVFilterInOut **inputs,
>                            AVFilterInOut **outputs)
> @@ -429,6 +453,9 @@ int avfilter_graph_parse2(AVFilterGraph *graph, const char *filters,
>      if ((ret = parse_sws_flags(&filters, graph)) < 0)
>          goto fail;
>  
> +    if ((ret = parse_scale_sws_opts(&filters, graph)) < 0)
> +        goto fail;
> +
>      do {
>          AVFilterContext *filter;
>          filters += strspn(filters, WHITESPACES);
>

Andreas:
On Sat, Aug 7, 2021 at 9:52 PM Andreas Rheinhardt <
andreas.rheinhardt@outlook.com> wrote:

> Linjie Fu:
> > From: Linjie Fu <linjie.justin.fu@gmail.com>
> >
> > To pass the swscale options for the inserted scalers.
> >
> > ffmpeg -i input.mp4 -filter_complex \
> >     "scale_sws_opts=alphablend=checkerboard;format=nv12" \
> >     -t 0.5 output.mp4
> >
> > Update docs.
> >
> > Signed-off-by: Linjie Fu <linjie.justin.fu@gmail.com>
> > ---
> >  doc/filters.texi          |  7 ++++---
> >  libavfilter/graphparser.c | 27 +++++++++++++++++++++++++++
> >  2 files changed, 31 insertions(+), 3 deletions(-)
> >
> > diff --git a/doc/filters.texi b/doc/filters.texi
> > index 790d165433..dbbb3a6940 100644
> > --- a/doc/filters.texi
> > +++ b/doc/filters.texi
> > @@ -204,9 +204,9 @@ pads must be connected. A filtergraph is considered
> valid if all the
> >  filter input and output pads of all the filterchains are connected.
> >
> >  Libavfilter will automatically insert @ref{scale} filters where format
> > -conversion is required. It is possible to specify swscale flags
> > -for those automatically inserted scalers by prepending
> > -@code{sws_flags=@var{flags};}
> > +conversion is required. It is possible to specify swscale flags or
> > +scale_sws_opts for those automatically inserted scalers by prepending
> > +@code{sws_flags=@var{flags};} or
> @code{scale_sws_opts=@var{scale_sws_opts};}
> >  to the filtergraph description.
> >
> >  Here is a BNF description of the filtergraph syntax:
> > @@ -219,6 +219,7 @@ Here is a BNF description of the filtergraph syntax:
> >  @var{FILTER}           ::= [@var{LINKLABELS}] @var{FILTER_NAME} ["="
> @var{FILTER_ARGUMENTS}] [@var{LINKLABELS}]
> >  @var{FILTERCHAIN}      ::= @var{FILTER} [,@var{FILTERCHAIN}]
> >  @var{FILTERGRAPH}      ::= [sws_flags=@var{flags};] @var{FILTERCHAIN}
> [;@var{FILTERGRAPH}]
> > +@var{FILTERGRAPH}      ::= [scale_sws_opts=@var{opts};]
> @var{FILTERCHAIN} [;@var{FILTERGRAPH}]
> >  @end example
> >
> >  @anchor{filtergraph escaping}
> > diff --git a/libavfilter/graphparser.c b/libavfilter/graphparser.c
> > index 1385c3ae71..8c63d6454e 100644
> > --- a/libavfilter/graphparser.c
> > +++ b/libavfilter/graphparser.c
> > @@ -415,6 +415,30 @@ static int parse_sws_flags(const char **buf,
> AVFilterGraph *graph)
> >      return 0;
> >  }
> >
> > +static int parse_scale_sws_opts(const char **buf, AVFilterGraph *graph)
> > +{
> > +    char *p = strchr(*buf, ';');
> > +
> > +    if (strncmp(*buf, "scale_sws_opts=", 15)) {
>
> av_strstart()
>
> > +        return 0;
> > +    }
> > +
> > +    if (!p) {
> > +        av_log(graph, AV_LOG_ERROR, "scale_sws_opts not terminated with
> ';'.\n");
> > +        return AVERROR(EINVAL);
> > +    }
> > +
> > +    *buf += 15;
> > +
> > +    av_freep(&graph->scale_sws_opts);
> > +    if (!(graph->scale_sws_opts = av_mallocz(p - *buf + 1)))
> > +        return AVERROR(ENOMEM);
> > +    av_strlcpy(graph->scale_sws_opts, *buf, p - *buf + 1);
>
> av_strndup()
>

Yes, thanks for pointing this out.
This patch uses the similar code from current implementation[1],  hence I
guess it could be simplified too.

- linjie
[1]
https://github.com/FFmpeg/FFmpeg/blob/master/libavfilter/graphparser.c#L395