[FFmpeg-devel] [PATCH] avfilter/scale: refactor common code for scaling height/width expressions

Mark Thompson sw at jkqxz.net
Thu Feb 2 00:40:33 EET 2017


On 01/02/17 00:46, Aman Gupta wrote:
> From: Aman Gupta <aman at tmm1.net>
> 
> Implements support for height/width expressions in vf_scale_vaapi,
> by refactoring common code into a new libavfilter/scale.c

Nice!  Patch as a whole LGTM, some minor nits below.

> ---
>  libavfilter/Makefile         |   8 +--
>  libavfilter/scale.c          | 143 +++++++++++++++++++++++++++++++++++++++++++
>  libavfilter/scale.h          |  31 ++++++++++
>  libavfilter/vf_scale.c       | 109 +++------------------------------
>  libavfilter/vf_scale_npp.c   |  87 +++-----------------------
>  libavfilter/vf_scale_vaapi.c |  18 +++++-
>  6 files changed, 208 insertions(+), 188 deletions(-)
>  create mode 100644 libavfilter/scale.c
>  create mode 100644 libavfilter/scale.h
> 
> diff --git a/libavfilter/Makefile b/libavfilter/Makefile
> index 68a94be..3231f08 100644
> --- a/libavfilter/Makefile
> +++ b/libavfilter/Makefile
> @@ -257,10 +257,10 @@ OBJS-$(CONFIG_REPEATFIELDS_FILTER)           += vf_repeatfields.o
>  OBJS-$(CONFIG_REVERSE_FILTER)                += f_reverse.o
>  OBJS-$(CONFIG_ROTATE_FILTER)                 += vf_rotate.o
>  OBJS-$(CONFIG_SAB_FILTER)                    += vf_sab.o
> -OBJS-$(CONFIG_SCALE_FILTER)                  += vf_scale.o
> -OBJS-$(CONFIG_SCALE_NPP_FILTER)              += vf_scale_npp.o
> -OBJS-$(CONFIG_SCALE_VAAPI_FILTER)            += vf_scale_vaapi.o
> -OBJS-$(CONFIG_SCALE2REF_FILTER)              += vf_scale.o
> +OBJS-$(CONFIG_SCALE_FILTER)                  += vf_scale.o scale.o
> +OBJS-$(CONFIG_SCALE_NPP_FILTER)              += vf_scale_npp.o scale.o
> +OBJS-$(CONFIG_SCALE_VAAPI_FILTER)            += vf_scale_vaapi.o scale.o
> +OBJS-$(CONFIG_SCALE2REF_FILTER)              += vf_scale.o scale.o
>  OBJS-$(CONFIG_SELECT_FILTER)                 += f_select.o
>  OBJS-$(CONFIG_SELECTIVECOLOR_FILTER)         += vf_selectivecolor.o
>  OBJS-$(CONFIG_SENDCMD_FILTER)                += f_sendcmd.o
> diff --git a/libavfilter/scale.c b/libavfilter/scale.c
> new file mode 100644
> index 0000000..b0f4be2
> --- /dev/null
> +++ b/libavfilter/scale.c
> @@ -0,0 +1,143 @@
> +/*
> + * This file is part of FFmpeg.
> + *
> + * FFmpeg is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * FFmpeg is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with FFmpeg; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#include "scale.h"
> +
> +static const char *const var_names[] = {
> +    "PI",
> +    "PHI",
> +    "E",
> +    "in_w",   "iw",
> +    "in_h",   "ih",
> +    "out_w",  "ow",
> +    "out_h",  "oh",
> +    "a",
> +    "sar",
> +    "dar",
> +    "hsub",
> +    "vsub",
> +    "ohsub",
> +    "ovsub",
> +    NULL
> +};
> +
> +enum var_name {
> +    VAR_PI,
> +    VAR_PHI,
> +    VAR_E,
> +    VAR_IN_W,   VAR_IW,
> +    VAR_IN_H,   VAR_IH,
> +    VAR_OUT_W,  VAR_OW,
> +    VAR_OUT_H,  VAR_OH,
> +    VAR_A,
> +    VAR_SAR,
> +    VAR_DAR,
> +    VAR_HSUB,
> +    VAR_VSUB,
> +    VAR_OHSUB,
> +    VAR_OVSUB,
> +    VARS_NB
> +};
> +
> +int ff_scale_eval_dimensions(void *ctx,
> +    const char *w_expr, const char *h_expr,
> +    AVFilterLink *inlink, AVFilterLink *outlink,
> +    int *ret_w, int *ret_h)
> +{
> +    const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(inlink->format);
> +    const AVPixFmtDescriptor *out_desc = av_pix_fmt_desc_get(outlink->format);
> +    const char *expr;
> +    int w, h;
> +    int factor_w, factor_h;
> +    int eval_w, eval_h;
> +    int ret;
> +    double var_values[VARS_NB], res;
> +
> +    var_values[VAR_IN_W]  = var_values[VAR_IW] = inlink->w;
> +    var_values[VAR_IN_H]  = var_values[VAR_IH] = inlink->h;
> +    var_values[VAR_OUT_W] = var_values[VAR_OW] = NAN;
> +    var_values[VAR_OUT_H] = var_values[VAR_OH] = NAN;
> +    var_values[VAR_A]     = (double) inlink->w / inlink->h;
> +    var_values[VAR_SAR]   = inlink->sample_aspect_ratio.num ?
> +        (double) inlink->sample_aspect_ratio.num / inlink->sample_aspect_ratio.den : 1;
> +    var_values[VAR_DAR]   = var_values[VAR_A] * var_values[VAR_SAR];
> +    var_values[VAR_HSUB]  = 1 << desc->log2_chroma_w;
> +    var_values[VAR_VSUB]  = 1 << desc->log2_chroma_h;
> +    var_values[VAR_OHSUB] = 1 << out_desc->log2_chroma_w;
> +    var_values[VAR_OVSUB] = 1 << out_desc->log2_chroma_h;
> +
> +    /* evaluate width and height */
> +    av_expr_parse_and_eval(&res, (expr = w_expr),
> +                           var_names, var_values,
> +                           NULL, NULL, NULL, NULL, NULL, 0, ctx);
> +    eval_w = var_values[VAR_OUT_W] = var_values[VAR_OW] = res;
> +
> +    if ((ret = av_expr_parse_and_eval(&res, (expr = h_expr),
> +                                      var_names, var_values,
> +                                      NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)
> +        goto fail;
> +    eval_h = var_values[VAR_OUT_H] = var_values[VAR_OH] = res;
> +    /* evaluate again the width, as it may depend on the output height */
> +    if ((ret = av_expr_parse_and_eval(&res, (expr = w_expr),
> +                                      var_names, var_values,
> +                                      NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)
> +        goto fail;
> +    eval_w = res;
> +
> +    w = eval_w;
> +    h = eval_h;
> +
> +    /* Check if it is requested that the result has to be divisible by a some
> +     * factor (w or h = -n with n being the factor). */
> +    factor_w = 1;
> +    factor_h = 1;
> +    if (w < -1) {
> +        factor_w = -w;
> +    }
> +    if (h < -1) {
> +        factor_h = -h;
> +    }
> +
> +    if (w < 0 && h < 0)
> +        eval_w = eval_h = 0;
> +
> +    if (!(w = eval_w))
> +        w = inlink->w;
> +    if (!(h = eval_h))
> +        h = inlink->h;
> +
> +    /* Make sure that the result is divisible by the factor we determined
> +     * earlier. If no factor was set, it is nothing will happen as the default
> +     * factor is 1 */
> +    if (w < 0)
> +        w = av_rescale(h, inlink->w, inlink->h * factor_w) * factor_w;
> +    if (h < 0)
> +        h = av_rescale(w, inlink->h, inlink->w * factor_h) * factor_h;
> +
> +    *ret_w = w;
> +    *ret_h = h;
> +
> +    return 0;
> +
> +fail:
> +    av_log(NULL, AV_LOG_ERROR,
> +           "Error when evaluating the expression '%s'.\n"
> +           "Maybe the expression for out_w:'%s' or for out_h:'%s' is self-referencing.\n",
> +           expr, w_expr, h_expr);
> +    return ret;
> +}
> diff --git a/libavfilter/scale.h b/libavfilter/scale.h
> new file mode 100644
> index 0000000..c95515d
> --- /dev/null
> +++ b/libavfilter/scale.h
> @@ -0,0 +1,31 @@
> +/*
> + * This file is part of FFmpeg.
> + *
> + * FFmpeg is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * FFmpeg is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with FFmpeg; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#ifndef AVFILTER_SCALE_H
> +#define AVFILTER_SCALE_H
> +
> +#include <stdint.h>
> +#include "avfilter.h"
> +#include "libavutil/eval.h"
> +#include "libavutil/pixdesc.h"

You don't need all of these includes in the header; they should go in scale.c.

> +
> +int ff_scale_eval_dimensions(void *ctx,
> +    const char *w_expr, const char *h_expr,
> +    AVFilterLink *inlink, AVFilterLink *outlink,
> +    int *ret_w, int *ret_h);
> +#endif
> diff --git a/libavfilter/vf_scale.c b/libavfilter/vf_scale.c
> index 22bee96..8645da7 100644
> --- a/libavfilter/vf_scale.c
> +++ b/libavfilter/vf_scale.c
> @@ -29,9 +29,9 @@
>  #include "avfilter.h"
>  #include "formats.h"
>  #include "internal.h"
> +#include "scale.h"
>  #include "video.h"
>  #include "libavutil/avstring.h"
> -#include "libavutil/eval.h"
>  #include "libavutil/internal.h"
>  #include "libavutil/mathematics.h"
>  #include "libavutil/opt.h"
> @@ -41,43 +41,12 @@
>  #include "libavutil/avassert.h"
>  #include "libswscale/swscale.h"
>  
> -static const char *const var_names[] = {
> -    "in_w",   "iw",
> -    "in_h",   "ih",
> -    "out_w",  "ow",
> -    "out_h",  "oh",
> -    "a",
> -    "sar",
> -    "dar",
> -    "hsub",
> -    "vsub",
> -    "ohsub",
> -    "ovsub",
> -    NULL
> -};
> -
> -enum var_name {
> -    VAR_IN_W,   VAR_IW,
> -    VAR_IN_H,   VAR_IH,
> -    VAR_OUT_W,  VAR_OW,
> -    VAR_OUT_H,  VAR_OH,
> -    VAR_A,
> -    VAR_SAR,
> -    VAR_DAR,
> -    VAR_HSUB,
> -    VAR_VSUB,
> -    VAR_OHSUB,
> -    VAR_OVSUB,
> -    VARS_NB
> -};
> -
>  enum EvalMode {
>      EVAL_MODE_INIT,
>      EVAL_MODE_FRAME,
>      EVAL_MODE_NB
>  };
>  
> -
>  typedef struct ScaleContext {
>      const AVClass *class;
>      struct SwsContext *sws;     ///< software scaler context
> @@ -256,74 +225,16 @@ static int config_props(AVFilterLink *outlink)
>                              outlink->src->inputs[1] :
>                              outlink->src->inputs[0];
>      enum AVPixelFormat outfmt = outlink->format;
> -    ScaleContext *scale = ctx->priv;
>      const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(inlink->format);
> -    const AVPixFmtDescriptor *out_desc = av_pix_fmt_desc_get(outlink->format);
> -    int64_t w, h;
> -    double var_values[VARS_NB], res;
> -    char *expr;
> +    ScaleContext *scale = ctx->priv;
> +    int w, h;
>      int ret;
> -    int factor_w, factor_h;
> -
> -    var_values[VAR_IN_W]  = var_values[VAR_IW] = inlink->w;
> -    var_values[VAR_IN_H]  = var_values[VAR_IH] = inlink->h;
> -    var_values[VAR_OUT_W] = var_values[VAR_OW] = NAN;
> -    var_values[VAR_OUT_H] = var_values[VAR_OH] = NAN;
> -    var_values[VAR_A]     = (double) inlink->w / inlink->h;
> -    var_values[VAR_SAR]   = inlink->sample_aspect_ratio.num ?
> -        (double) inlink->sample_aspect_ratio.num / inlink->sample_aspect_ratio.den : 1;
> -    var_values[VAR_DAR]   = var_values[VAR_A] * var_values[VAR_SAR];
> -    var_values[VAR_HSUB]  = 1 << desc->log2_chroma_w;
> -    var_values[VAR_VSUB]  = 1 << desc->log2_chroma_h;
> -    var_values[VAR_OHSUB] = 1 << out_desc->log2_chroma_w;
> -    var_values[VAR_OVSUB] = 1 << out_desc->log2_chroma_h;
> -
> -    /* evaluate width and height */
> -    av_expr_parse_and_eval(&res, (expr = scale->w_expr),
> -                           var_names, var_values,
> -                           NULL, NULL, NULL, NULL, NULL, 0, ctx);
> -    scale->w = var_values[VAR_OUT_W] = var_values[VAR_OW] = res;
> -    if ((ret = av_expr_parse_and_eval(&res, (expr = scale->h_expr),
> -                                      var_names, var_values,
> -                                      NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)
> -        goto fail;
> -    scale->h = var_values[VAR_OUT_H] = var_values[VAR_OH] = res;
> -    /* evaluate again the width, as it may depend on the output height */
> -    if ((ret = av_expr_parse_and_eval(&res, (expr = scale->w_expr),
> -                                      var_names, var_values,
> -                                      NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)
> -        goto fail;
> -    scale->w = res;
> -
> -    w = scale->w;
> -    h = scale->h;
> -
> -    /* Check if it is requested that the result has to be divisible by a some
> -     * factor (w or h = -n with n being the factor). */
> -    factor_w = 1;
> -    factor_h = 1;
> -    if (w < -1) {
> -        factor_w = -w;
> -    }
> -    if (h < -1) {
> -        factor_h = -h;
> -    }
> -
> -    if (w < 0 && h < 0)
> -        scale->w = scale->h = 0;
>  
> -    if (!(w = scale->w))
> -        w = inlink->w;
> -    if (!(h = scale->h))
> -        h = inlink->h;
> -
> -    /* Make sure that the result is divisible by the factor we determined
> -     * earlier. If no factor was set, it is nothing will happen as the default
> -     * factor is 1 */
> -    if (w < 0)
> -        w = av_rescale(h, inlink->w, inlink->h * factor_w) * factor_w;
> -    if (h < 0)
> -        h = av_rescale(w, inlink->h, inlink->w * factor_h) * factor_h;
> +    if ((ret = ff_scale_eval_dimensions(ctx,
> +                                        scale->w_expr, scale->h_expr,
> +                                        inlink, outlink,
> +                                        &w, &h)) < 0)
> +        goto fail;
>  
>      /* Note that force_original_aspect_ratio may overwrite the previous set
>       * dimensions so that it is not divisible by the set factors anymore. */
> @@ -439,10 +350,6 @@ static int config_props(AVFilterLink *outlink)
>      return 0;
>  
>  fail:
> -    av_log(NULL, AV_LOG_ERROR,
> -           "Error when evaluating the expression '%s'.\n"
> -           "Maybe the expression for out_w:'%s' or for out_h:'%s' is self-referencing.\n",
> -           expr, scale->w_expr, scale->h_expr);
>      return ret;
>  }
>  
> diff --git a/libavfilter/vf_scale_npp.c b/libavfilter/vf_scale_npp.c
> index 1abfdd1..84d88eb 100644
> --- a/libavfilter/vf_scale_npp.c
> +++ b/libavfilter/vf_scale_npp.c
> @@ -27,7 +27,6 @@
>  
>  #include "libavutil/avstring.h"
>  #include "libavutil/common.h"
> -#include "libavutil/eval.h"
>  #include "libavutil/hwcontext.h"
>  #include "libavutil/hwcontext_cuda_internal.h"
>  #include "libavutil/internal.h"
> @@ -38,6 +37,7 @@
>  #include "avfilter.h"
>  #include "formats.h"
>  #include "internal.h"
> +#include "scale.h"
>  #include "video.h"
>  
>  static const enum AVPixelFormat supported_formats[] = {
> @@ -50,32 +50,6 @@ static const enum AVPixelFormat deinterleaved_formats[][2] = {
>      { AV_PIX_FMT_NV12, AV_PIX_FMT_YUV420P },
>  };
>  
> -static const char *const var_names[] = {
> -    "PI",
> -    "PHI",
> -    "E",
> -    "in_w",   "iw",
> -    "in_h",   "ih",
> -    "out_w",  "ow",
> -    "out_h",  "oh",
> -    "a", "dar",
> -    "sar",
> -    NULL
> -};
> -
> -enum var_name {
> -    VAR_PI,
> -    VAR_PHI,
> -    VAR_E,
> -    VAR_IN_W,   VAR_IW,
> -    VAR_IN_H,   VAR_IH,
> -    VAR_OUT_W,  VAR_OW,
> -    VAR_OUT_H,  VAR_OH,
> -    VAR_A, VAR_DAR,
> -    VAR_SAR,
> -    VARS_NB
> -};
> -
>  enum ScaleStage {
>      STAGE_DEINTERLEAVE,
>      STAGE_RESIZE,
> @@ -359,60 +333,15 @@ static int nppscale_config_props(AVFilterLink *outlink)
>  {
>      AVFilterContext *ctx = outlink->src;
>      AVFilterLink *inlink = outlink->src->inputs[0];
> -    NPPScaleContext  *s = ctx->priv;
> -    int64_t w, h;
> -    double var_values[VARS_NB], res;
> -    char *expr;
> +    NPPScaleContext *s = ctx->priv;
> +    int w, h;
>      int ret;
>  
> -    var_values[VAR_PI]    = M_PI;
> -    var_values[VAR_PHI]   = M_PHI;
> -    var_values[VAR_E]     = M_E;
> -    var_values[VAR_IN_W]  = var_values[VAR_IW] = inlink->w;
> -    var_values[VAR_IN_H]  = var_values[VAR_IH] = inlink->h;
> -    var_values[VAR_OUT_W] = var_values[VAR_OW] = NAN;
> -    var_values[VAR_OUT_H] = var_values[VAR_OH] = NAN;
> -    var_values[VAR_A]     = (double) inlink->w / inlink->h;
> -    var_values[VAR_SAR]   = inlink->sample_aspect_ratio.num ?
> -        (double) inlink->sample_aspect_ratio.num / inlink->sample_aspect_ratio.den : 1;
> -    var_values[VAR_DAR]   = var_values[VAR_A] * var_values[VAR_SAR];
> -
> -    /* evaluate width and height */
> -    av_expr_parse_and_eval(&res, (expr = s->w_expr),
> -                           var_names, var_values,
> -                           NULL, NULL, NULL, NULL, NULL, 0, ctx);
> -    s->w = var_values[VAR_OUT_W] = var_values[VAR_OW] = res;
> -    if ((ret = av_expr_parse_and_eval(&res, (expr = s->h_expr),
> -                                      var_names, var_values,
> -                                      NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)
> +    if ((ret = ff_scale_eval_dimensions(s,
> +                                        s->w_expr, s->h_expr,
> +                                        inlink, outlink,
> +                                        &w, &h)) < 0)
>          goto fail;
> -    s->h = var_values[VAR_OUT_H] = var_values[VAR_OH] = res;
> -    /* evaluate again the width, as it may depend on the output height */
> -    if ((ret = av_expr_parse_and_eval(&res, (expr = s->w_expr),
> -                                      var_names, var_values,
> -                                      NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0)
> -        goto fail;
> -    s->w = res;
> -
> -    w = s->w;
> -    h = s->h;
> -
> -    /* sanity check params */
> -    if (w <  -1 || h <  -1) {
> -        av_log(ctx, AV_LOG_ERROR, "Size values less than -1 are not acceptable.\n");
> -        return AVERROR(EINVAL);
> -    }
> -    if (w == -1 && h == -1)
> -        s->w = s->h = 0;
> -
> -    if (!(w = s->w))
> -        w = inlink->w;
> -    if (!(h = s->h))
> -        h = inlink->h;
> -    if (w == -1)
> -        w = av_rescale(h, inlink->w, inlink->h);
> -    if (h == -1)
> -        h = av_rescale(w, inlink->h, inlink->w);
>  
>      if (w > INT_MAX || h > INT_MAX ||
>          (h * inlink->w) > INT_MAX  ||
>         (w * inlink->h) > INT_MAX)
>         av_log(ctx, AV_LOG_ERROR, "Rescaled value for width or height is too big.\n");

This test doesn't work any more - all of w, h and the corresponding AVFilterLink fields are int, so the test will just invoke undefined behaviour on signed overflow rather than testing anything.

Add some casts, I think?  (I assume this is trying to enforce some constraint of the npp API.)

> @@ -439,8 +368,6 @@ static int nppscale_config_props(AVFilterLink *outlink)
>      return 0;
>  
>  fail:
> -    av_log(NULL, AV_LOG_ERROR,
> -           "Error when evaluating the expression '%s'\n", expr);
>      return ret;
>  }
>  
> diff --git a/libavfilter/vf_scale_vaapi.c b/libavfilter/vf_scale_vaapi.c
> index d1cb246..1abb42e 100644
> --- a/libavfilter/vf_scale_vaapi.c
> +++ b/libavfilter/vf_scale_vaapi.c
> @@ -31,6 +31,7 @@
>  #include "avfilter.h"
>  #include "formats.h"
>  #include "internal.h"
> +#include "scale.h"
>  
>  typedef struct ScaleVAAPIContext {
>      const AVClass *class;
> @@ -50,9 +51,13 @@ typedef struct ScaleVAAPIContext {
>  
>      char *output_format_string;
>      enum AVPixelFormat output_format;
> +
> +    char *w_expr;               ///< width  expression string
> +    char *h_expr;               ///< height expression string
> +
> +    /* computed width/height */

Keep the comment style consistent?  (I'd go for // and no doxygen markers, but anything consistent is fine.)

>      int output_width;
>      int output_height;
> -
>  } ScaleVAAPIContext;
>  
>  
> @@ -110,6 +115,7 @@ static int scale_vaapi_config_input(AVFilterLink *inlink)
>  
>  static int scale_vaapi_config_output(AVFilterLink *outlink)
>  {
> +    AVFilterLink *inlink = outlink->src->inputs[0];
>      AVFilterContext *avctx = outlink->src;
>      ScaleVAAPIContext *ctx = avctx->priv;
>      AVVAAPIHWConfig *hwconfig = NULL;
> @@ -162,6 +168,12 @@ static int scale_vaapi_config_output(AVFilterLink *outlink)
>          }
>      }
>  
> +    if ((err = ff_scale_eval_dimensions(ctx,
> +                                        ctx->w_expr, ctx->h_expr,
> +                                        inlink, outlink,
> +                                        &ctx->output_width, &ctx->output_height)) < 0)
> +        goto fail;
> +
>      if (ctx->output_width  < constraints->min_width  ||
>          ctx->output_height < constraints->min_height ||
>          ctx->output_width  > constraints->max_width  ||
> @@ -414,9 +426,9 @@ static av_cold void scale_vaapi_uninit(AVFilterContext *avctx)
>  #define FLAGS (AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM)
>  static const AVOption scale_vaapi_options[] = {
>      { "w", "Output video width",
> -      OFFSET(output_width),  AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, .flags = FLAGS },
> +      OFFSET(w_expr), AV_OPT_TYPE_STRING, {.str = "iw"}, .flags = FLAGS },
>      { "h", "Output video height",
> -      OFFSET(output_height), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, .flags = FLAGS },
> +      OFFSET(h_expr), AV_OPT_TYPE_STRING, {.str = "ih"}, .flags = FLAGS },
>      { "format", "Output video format (software format of hardware frames)",
>        OFFSET(output_format_string), AV_OPT_TYPE_STRING, .flags = FLAGS },
>      { NULL },
> 


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