[FFmpeg-devel] [PATCH 5/8] sws: add a new scaling API

[Anton Khirnov]

Quoting Michael Niedermayer (2021-07-12 21:08:55)
> On Mon, Jul 12, 2021 at 01:07:06PM +0200, Anton Khirnov wrote:
> [...]
> > diff --git a/libswscale/swscale.h b/libswscale/swscale.h
> > index 50d6d46553..41eacd2dea 100644
> > --- a/libswscale/swscale.h
> > +++ b/libswscale/swscale.h
> > @@ -30,6 +30,7 @@
> >  #include <stdint.h>
> >  
> >  #include "libavutil/avutil.h"
> > +#include "libavutil/frame.h"
> >  #include "libavutil/log.h"
> >  #include "libavutil/pixfmt.h"
> >  #include "version.h"
> > @@ -218,6 +219,85 @@ int sws_scale(struct SwsContext *c, const uint8_t *const srcSlice[],
> >                const int srcStride[], int srcSliceY, int srcSliceH,
> >                uint8_t *const dst[], const int dstStride[]);
> >  
> > +/**
> > + * Scale source data from src and write the output to dst.
> > + *
> > + * This is merely a convenience wrapper around
> > + * - sws_frame_start()
> > + * - sws_send_slice(0, src->height)
> > + * - sws_receive_slice(0, dst->height)
> > + * - sws_frame_end()
> > + *
> > + * @param dst The destination frame. See documentation for sws_frame_start() for
> > + *            more details.
> > + * @param src The source frame.
> > + *
> > + * @return 0 on success, a negative AVERROR code on failure
> > + */
> > +int sws_scale_frame(struct SwsContext *c, AVFrame *dst, const AVFrame *src);
> > +
> > +/**
> > + * Initialize the scaling process for a given pair of source/destination frames.
> > + * Must be called before any calls to sws_send_slice() and sws_receive_slice().
> > + *
> > + * This function will retain references to src and dst.
> > + *
> > + * @param dst The destination frame.
> > + *
> > + *            The data buffers may either be already allocated by the caller or
> > + *            left clear, in which case they will be allocated by the scaler.
> > + *            The latter may have performance advantages - e.g. in certain cases
> > + *            some output planes may be references to input planes, rather than
> > + *            copies.
> > + *
> > + *            Output data will be written into this frame in successful
> > + *            sws_receive_slice() calls.
> > + * @param src The source frame. The data buffers must be allocated, but the
> > + *            frame data does not have to be ready at this point. Data
> > + *            availability is then signalled by sws_send_slice().
> > + * @return 0 on success, a negative AVERROR code on failure
> > + *
> > + * @see sws_frame_end()
> > + */
> > +int sws_frame_start(struct SwsContext *c, AVFrame *dst, const AVFrame *src);
> > +
> > +/**
> > + * Finish the scaling process for a pair of source/destination frames previously
> > + * submitted with sws_frame_start(). Must be called after all sws_send_slice()
> > + * and sws_receive_slice() calls are done, before any new sws_frame_start()
> > + * calls.
> > + */
> > +void sws_frame_end(struct SwsContext *c);
> > +
> 
> > +/**
> > + * Indicate that a horizontal slice of input data is available in the source
> > + * frame previously provided to sws_frame_start(). The slices may be provided in
> > + * any order, but may not overlap. For vertically subsampled pixel formats, the
> > + * slices must be aligned according to subsampling.
> > + *
> > + * @param slice_start first row of the slice
> > + * @param slice_height number of rows in the slice
> > + *
> > + * @return 0 on success, a negative AVERROR code on failure.
> > + */
> > +int sws_send_slice(struct SwsContext *c, unsigned int slice_start,
> > +                   unsigned int slice_height);
> 
> I suggest to use non 0 on success.

Outright >0, or >= 0?

> That could then be extended in the future for example to provide information
> about how many lines have already been consumed and its memory be reused

I will amend the patch.

Are you satisfied with the API otherwise?

-- 
Anton Khirnov