X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=libavfilter%2Fvf_scale.c;h=3add31bace47572856800c9e2be2e317e958eeeb;hb=d7e0d428faaa04e2fd850eca82f314ca2ad3dfe5;hp=41ddec766188486c17eaf668ff1321158a0ea582;hpb=b9d479bac45bb4ce42b3f685bce5cad8d89f8f71;p=ffmpeg

diff --git a/libavfilter/vf_scale.c b/libavfilter/vf_scale.c
index 41ddec76618..3add31bace4 100644
--- a/libavfilter/vf_scale.c
+++ b/libavfilter/vf_scale.c
@@ -29,9 +29,10 @@
 #include "avfilter.h"
 #include "formats.h"
 #include "internal.h"
-#include "scale.h"
+#include "scale_eval.h"
 #include "video.h"
 #include "libavutil/avstring.h"
+#include "libavutil/eval.h"
 #include "libavutil/internal.h"
 #include "libavutil/mathematics.h"
 #include "libavutil/opt.h"
@@ -41,6 +42,62 @@
 #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",
+    "n",
+    "t",
+    "pos",
+    "main_w",
+    "main_h",
+    "main_a",
+    "main_sar",
+    "main_dar", "mdar",
+    "main_hsub",
+    "main_vsub",
+    "main_n",
+    "main_t",
+    "main_pos",
+    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,
+    VAR_N,
+    VAR_T,
+    VAR_POS,
+    VAR_S2R_MAIN_W,
+    VAR_S2R_MAIN_H,
+    VAR_S2R_MAIN_A,
+    VAR_S2R_MAIN_SAR,
+    VAR_S2R_MAIN_DAR, VAR_S2R_MDAR,
+    VAR_S2R_MAIN_HSUB,
+    VAR_S2R_MAIN_VSUB,
+    VAR_S2R_MAIN_N,
+    VAR_S2R_MAIN_T,
+    VAR_S2R_MAIN_POS,
+    VARS_NB
+};
+
 enum EvalMode {
     EVAL_MODE_INIT,
     EVAL_MODE_FRAME,
@@ -72,6 +129,10 @@ typedef struct ScaleContext {
 
     char *w_expr;               ///< width  expression string
     char *h_expr;               ///< height expression string
+    AVExpr *w_pexpr;
+    AVExpr *h_pexpr;
+    double var_values[VARS_NB];
+
     char *flags_str;
 
     char *in_color_matrix;
@@ -96,6 +157,119 @@ typedef struct ScaleContext {
 
 AVFilter ff_vf_scale2ref;
 
+static int config_props(AVFilterLink *outlink);
+
+static int check_exprs(AVFilterContext *ctx)
+{
+    ScaleContext *scale = ctx->priv;
+    unsigned vars_w[VARS_NB] = { 0 }, vars_h[VARS_NB] = { 0 };
+
+    if (!scale->w_pexpr && !scale->h_pexpr)
+        return AVERROR(EINVAL);
+
+    if (scale->w_pexpr)
+        av_expr_count_vars(scale->w_pexpr, vars_w, VARS_NB);
+    if (scale->h_pexpr)
+        av_expr_count_vars(scale->h_pexpr, vars_h, VARS_NB);
+
+    if (vars_w[VAR_OUT_W] || vars_w[VAR_OW]) {
+        av_log(ctx, AV_LOG_ERROR, "Width expression cannot be self-referencing: '%s'.\n", scale->w_expr);
+        return AVERROR(EINVAL);
+    }
+
+    if (vars_h[VAR_OUT_H] || vars_h[VAR_OH]) {
+        av_log(ctx, AV_LOG_ERROR, "Height expression cannot be self-referencing: '%s'.\n", scale->h_expr);
+        return AVERROR(EINVAL);
+    }
+
+    if ((vars_w[VAR_OUT_H] || vars_w[VAR_OH]) &&
+        (vars_h[VAR_OUT_W] || vars_h[VAR_OW])) {
+        av_log(ctx, AV_LOG_WARNING, "Circular references detected for width '%s' and height '%s' - possibly invalid.\n", scale->w_expr, scale->h_expr);
+    }
+
+    if (ctx->filter != &ff_vf_scale2ref &&
+        (vars_w[VAR_S2R_MAIN_W]    || vars_h[VAR_S2R_MAIN_W]    ||
+         vars_w[VAR_S2R_MAIN_H]    || vars_h[VAR_S2R_MAIN_H]    ||
+         vars_w[VAR_S2R_MAIN_A]    || vars_h[VAR_S2R_MAIN_A]    ||
+         vars_w[VAR_S2R_MAIN_SAR]  || vars_h[VAR_S2R_MAIN_SAR]  ||
+         vars_w[VAR_S2R_MAIN_DAR]  || vars_h[VAR_S2R_MAIN_DAR]  ||
+         vars_w[VAR_S2R_MDAR]      || vars_h[VAR_S2R_MDAR]      ||
+         vars_w[VAR_S2R_MAIN_HSUB] || vars_h[VAR_S2R_MAIN_HSUB] ||
+         vars_w[VAR_S2R_MAIN_VSUB] || vars_h[VAR_S2R_MAIN_VSUB] ||
+         vars_w[VAR_S2R_MAIN_N]    || vars_h[VAR_S2R_MAIN_N]    ||
+         vars_w[VAR_S2R_MAIN_T]    || vars_h[VAR_S2R_MAIN_T]    ||
+         vars_w[VAR_S2R_MAIN_POS]  || vars_h[VAR_S2R_MAIN_POS]) ) {
+        av_log(ctx, AV_LOG_ERROR, "Expressions with scale2ref variables are not valid in scale filter.\n");
+        return AVERROR(EINVAL);
+    }
+
+    if (scale->eval_mode == EVAL_MODE_INIT &&
+        (vars_w[VAR_N]            || vars_h[VAR_N]           ||
+         vars_w[VAR_T]            || vars_h[VAR_T]           ||
+         vars_w[VAR_POS]          || vars_h[VAR_POS]         ||
+         vars_w[VAR_S2R_MAIN_N]   || vars_h[VAR_S2R_MAIN_N]  ||
+         vars_w[VAR_S2R_MAIN_T]   || vars_h[VAR_S2R_MAIN_T]  ||
+         vars_w[VAR_S2R_MAIN_POS] || vars_h[VAR_S2R_MAIN_POS]) ) {
+        av_log(ctx, AV_LOG_ERROR, "Expressions with frame variables 'n', 't', 'pos' are not valid in init eval_mode.\n");
+        return AVERROR(EINVAL);
+    }
+
+    return 0;
+}
+
+static int scale_parse_expr(AVFilterContext *ctx, char *str_expr, AVExpr **pexpr_ptr, const char *var, const char *args)
+{
+    ScaleContext *scale = ctx->priv;
+    int ret, is_inited = 0;
+    char *old_str_expr = NULL;
+    AVExpr *old_pexpr = NULL;
+
+    if (str_expr) {
+        old_str_expr = av_strdup(str_expr);
+        if (!old_str_expr)
+            return AVERROR(ENOMEM);
+        av_opt_set(scale, var, args, 0);
+    }
+
+    if (*pexpr_ptr) {
+        old_pexpr = *pexpr_ptr;
+        *pexpr_ptr = NULL;
+        is_inited = 1;
+    }
+
+    ret = av_expr_parse(pexpr_ptr, args, var_names,
+                        NULL, NULL, NULL, NULL, 0, ctx);
+    if (ret < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Cannot parse expression for %s: '%s'\n", var, args);
+        goto revert;
+    }
+
+    ret = check_exprs(ctx);
+    if (ret < 0)
+        goto revert;
+
+    if (is_inited && (ret = config_props(ctx->outputs[0])) < 0)
+        goto revert;
+
+    av_expr_free(old_pexpr);
+    old_pexpr = NULL;
+    av_freep(&old_str_expr);
+
+    return 0;
+
+revert:
+    av_expr_free(*pexpr_ptr);
+    *pexpr_ptr = NULL;
+    if (old_str_expr) {
+        av_opt_set(scale, var, old_str_expr, 0);
+        av_free(old_str_expr);
+    }
+    if (old_pexpr)
+        *pexpr_ptr = old_pexpr;
+
+    return ret;
+}
+
 static av_cold int init_dict(AVFilterContext *ctx, AVDictionary **opts)
 {
     ScaleContext *scale = ctx->priv;
@@ -127,6 +301,14 @@ static av_cold int init_dict(AVFilterContext *ctx, AVDictionary **opts)
     if (!scale->h_expr)
         av_opt_set(scale, "h", "ih", 0);
 
+    ret = scale_parse_expr(ctx, NULL, &scale->w_pexpr, "width", scale->w_expr);
+    if (ret < 0)
+        return ret;
+
+    ret = scale_parse_expr(ctx, NULL, &scale->h_pexpr, "height", scale->h_expr);
+    if (ret < 0)
+        return ret;
+
     av_log(ctx, AV_LOG_VERBOSE, "w:%s h:%s flags:'%s' interl:%d\n",
            scale->w_expr, scale->h_expr, (char *)av_x_if_null(scale->flags_str, ""), scale->interlaced);
 
@@ -149,6 +331,9 @@ static av_cold int init_dict(AVFilterContext *ctx, AVDictionary **opts)
 static av_cold void uninit(AVFilterContext *ctx)
 {
     ScaleContext *scale = ctx->priv;
+    av_expr_free(scale->w_pexpr);
+    av_expr_free(scale->h_pexpr);
+    scale->w_pexpr = scale->h_pexpr = NULL;
     sws_freeContext(scale->sws);
     sws_freeContext(scale->isws[0]);
     sws_freeContext(scale->isws[1]);
@@ -173,7 +358,7 @@ static int query_formats(AVFilterContext *ctx)
                 return ret;
             }
         }
-        if ((ret = ff_formats_ref(formats, &ctx->inputs[0]->out_formats)) < 0)
+        if ((ret = ff_formats_ref(formats, &ctx->inputs[0]->outcfg.formats)) < 0)
             return ret;
     }
     if (ctx->outputs[0]) {
@@ -187,7 +372,7 @@ static int query_formats(AVFilterContext *ctx)
                 return ret;
             }
         }
-        if ((ret = ff_formats_ref(formats, &ctx->outputs[0]->in_formats)) < 0)
+        if ((ret = ff_formats_ref(formats, &ctx->outputs[0]->incfg.formats)) < 0)
             return ret;
     }
 
@@ -218,6 +403,81 @@ static const int *parse_yuv_type(const char *s, enum AVColorSpace colorspace)
     return sws_getCoefficients(colorspace);
 }
 
+static int scale_eval_dimensions(AVFilterContext *ctx)
+{
+    ScaleContext *scale = ctx->priv;
+    const char scale2ref = ctx->filter == &ff_vf_scale2ref;
+    const AVFilterLink *inlink = scale2ref ? ctx->inputs[1] : ctx->inputs[0];
+    const AVFilterLink *outlink = ctx->outputs[0];
+    const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(inlink->format);
+    const AVPixFmtDescriptor *out_desc = av_pix_fmt_desc_get(outlink->format);
+    char *expr;
+    int eval_w, eval_h;
+    int ret;
+    double res;
+    const AVPixFmtDescriptor *main_desc;
+    const AVFilterLink *main_link;
+
+    if (scale2ref) {
+        main_link = ctx->inputs[0];
+        main_desc = av_pix_fmt_desc_get(main_link->format);
+    }
+
+    scale->var_values[VAR_IN_W]  = scale->var_values[VAR_IW] = inlink->w;
+    scale->var_values[VAR_IN_H]  = scale->var_values[VAR_IH] = inlink->h;
+    scale->var_values[VAR_OUT_W] = scale->var_values[VAR_OW] = NAN;
+    scale->var_values[VAR_OUT_H] = scale->var_values[VAR_OH] = NAN;
+    scale->var_values[VAR_A]     = (double) inlink->w / inlink->h;
+    scale->var_values[VAR_SAR]   = inlink->sample_aspect_ratio.num ?
+        (double) inlink->sample_aspect_ratio.num / inlink->sample_aspect_ratio.den : 1;
+    scale->var_values[VAR_DAR]   = scale->var_values[VAR_A] * scale->var_values[VAR_SAR];
+    scale->var_values[VAR_HSUB]  = 1 << desc->log2_chroma_w;
+    scale->var_values[VAR_VSUB]  = 1 << desc->log2_chroma_h;
+    scale->var_values[VAR_OHSUB] = 1 << out_desc->log2_chroma_w;
+    scale->var_values[VAR_OVSUB] = 1 << out_desc->log2_chroma_h;
+
+    if (scale2ref) {
+        scale->var_values[VAR_S2R_MAIN_W] = main_link->w;
+        scale->var_values[VAR_S2R_MAIN_H] = main_link->h;
+        scale->var_values[VAR_S2R_MAIN_A] = (double) main_link->w / main_link->h;
+        scale->var_values[VAR_S2R_MAIN_SAR] = main_link->sample_aspect_ratio.num ?
+            (double) main_link->sample_aspect_ratio.num / main_link->sample_aspect_ratio.den : 1;
+        scale->var_values[VAR_S2R_MAIN_DAR] = scale->var_values[VAR_S2R_MDAR] =
+            scale->var_values[VAR_S2R_MAIN_A] * scale->var_values[VAR_S2R_MAIN_SAR];
+        scale->var_values[VAR_S2R_MAIN_HSUB] = 1 << main_desc->log2_chroma_w;
+        scale->var_values[VAR_S2R_MAIN_VSUB] = 1 << main_desc->log2_chroma_h;
+    }
+
+    res = av_expr_eval(scale->w_pexpr, scale->var_values, NULL);
+    eval_w = scale->var_values[VAR_OUT_W] = scale->var_values[VAR_OW] = (int) res == 0 ? inlink->w : (int) res;
+
+    res = av_expr_eval(scale->h_pexpr, scale->var_values, NULL);
+    if (isnan(res)) {
+        expr = scale->h_expr;
+        ret = AVERROR(EINVAL);
+        goto fail;
+    }
+    eval_h = scale->var_values[VAR_OUT_H] = scale->var_values[VAR_OH] = (int) res == 0 ? inlink->h : (int) res;
+
+    res = av_expr_eval(scale->w_pexpr, scale->var_values, NULL);
+    if (isnan(res)) {
+        expr = scale->w_expr;
+        ret = AVERROR(EINVAL);
+        goto fail;
+    }
+    eval_w = scale->var_values[VAR_OUT_W] = scale->var_values[VAR_OW] = (int) res == 0 ? inlink->w : (int) res;
+
+    scale->w = eval_w;
+    scale->h = eval_h;
+
+    return 0;
+
+fail:
+    av_log(ctx, AV_LOG_ERROR,
+           "Error when evaluating the expression '%s'.\n", expr);
+    return ret;
+}
+
 static int config_props(AVFilterLink *outlink)
 {
     AVFilterContext *ctx = outlink->src;
@@ -228,55 +488,29 @@ static int config_props(AVFilterLink *outlink)
     enum AVPixelFormat outfmt = outlink->format;
     const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(inlink->format);
     ScaleContext *scale = ctx->priv;
-    int w, h;
     int ret;
 
-    if ((ret = ff_scale_eval_dimensions(ctx,
-                                        scale->w_expr, scale->h_expr,
-                                        inlink, outlink,
-                                        &w, &h)) < 0)
+    if ((ret = scale_eval_dimensions(ctx)) < 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
-     * unless force_divisible_by is defined as well */
-    if (scale->force_original_aspect_ratio) {
-        int tmp_w = av_rescale(h, inlink->w, inlink->h);
-        int tmp_h = av_rescale(w, inlink->h, inlink->w);
-
-        if (scale->force_original_aspect_ratio == 1) {
-             w = FFMIN(tmp_w, w);
-             h = FFMIN(tmp_h, h);
-             if (scale->force_divisible_by > 1) {
-                 // round down
-                 w = w / scale->force_divisible_by * scale->force_divisible_by;
-                 h = h / scale->force_divisible_by * scale->force_divisible_by;
-             }
-        } else {
-             w = FFMAX(tmp_w, w);
-             h = FFMAX(tmp_h, h);
-             if (scale->force_divisible_by > 1) {
-                 // round up
-                 w = (w + scale->force_divisible_by - 1) / scale->force_divisible_by * scale->force_divisible_by;
-                 h = (h + scale->force_divisible_by - 1) / scale->force_divisible_by * scale->force_divisible_by;
-             }
-        }
-    }
+    ff_scale_adjust_dimensions(inlink, &scale->w, &scale->h,
+                               scale->force_original_aspect_ratio,
+                               scale->force_divisible_by);
 
-    if (w > INT_MAX || h > INT_MAX ||
-        (h * inlink->w) > INT_MAX  ||
-        (w * inlink->h) > INT_MAX)
+    if (scale->w > INT_MAX ||
+        scale->h > INT_MAX ||
+        (scale->h * inlink->w) > INT_MAX ||
+        (scale->w * inlink->h) > INT_MAX)
         av_log(ctx, AV_LOG_ERROR, "Rescaled value for width or height is too big.\n");
 
-    outlink->w = w;
-    outlink->h = h;
+    outlink->w = scale->w;
+    outlink->h = scale->h;
 
     /* TODO: make algorithm configurable */
 
     scale->input_is_pal = desc->flags & AV_PIX_FMT_FLAG_PAL;
     if (outfmt == AV_PIX_FMT_PAL8) outfmt = AV_PIX_FMT_BGR8;
-    scale->output_is_pal = av_pix_fmt_desc_get(outfmt)->flags & AV_PIX_FMT_FLAG_PAL ||
-                           av_pix_fmt_desc_get(outfmt)->flags & FF_PSEUDOPAL;
+    scale->output_is_pal = av_pix_fmt_desc_get(outfmt)->flags & AV_PIX_FMT_FLAG_PAL;
 
     if (scale->sws)
         sws_freeContext(scale->sws);
@@ -400,8 +634,8 @@ static int scale_slice(AVFilterLink *link, AVFrame *out_buf, AVFrame *cur_pic, s
         int vsub= ((i+1)&2) ? scale->vsub : 0;
          in_stride[i] = cur_pic->linesize[i] * mul;
         out_stride[i] = out_buf->linesize[i] * mul;
-         in[i] = cur_pic->data[i] + ((y>>vsub)+field) * cur_pic->linesize[i];
-        out[i] = out_buf->data[i] +            field  * out_buf->linesize[i];
+         in[i] = FF_PTR_ADD(cur_pic->data[i], ((y>>vsub)+field) * cur_pic->linesize[i]);
+        out[i] = FF_PTR_ADD(out_buf->data[i],            field  * out_buf->linesize[i]);
     }
     if (scale->input_is_pal)
          in[1] = cur_pic->data[1];
@@ -414,28 +648,63 @@ static int scale_slice(AVFilterLink *link, AVFrame *out_buf, AVFrame *cur_pic, s
 
 static int scale_frame(AVFilterLink *link, AVFrame *in, AVFrame **frame_out)
 {
-    ScaleContext *scale = link->dst->priv;
-    AVFilterLink *outlink = link->dst->outputs[0];
+    AVFilterContext *ctx = link->dst;
+    ScaleContext *scale = ctx->priv;
+    AVFilterLink *outlink = ctx->outputs[0];
     AVFrame *out;
     const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(link->format);
     char buf[32];
     int in_range;
+    int frame_changed;
 
     *frame_out = NULL;
     if (in->colorspace == AVCOL_SPC_YCGCO)
         av_log(link->dst, AV_LOG_WARNING, "Detected unsupported YCgCo colorspace.\n");
 
-    if (  in->width  != link->w
-       || in->height != link->h
-       || in->format != link->format
-       || in->sample_aspect_ratio.den != link->sample_aspect_ratio.den || in->sample_aspect_ratio.num != link->sample_aspect_ratio.num) {
+    frame_changed = in->width  != link->w ||
+                    in->height != link->h ||
+                    in->format != link->format ||
+                    in->sample_aspect_ratio.den != link->sample_aspect_ratio.den ||
+                    in->sample_aspect_ratio.num != link->sample_aspect_ratio.num;
+
+    if (scale->eval_mode == EVAL_MODE_FRAME || frame_changed) {
         int ret;
+        unsigned vars_w[VARS_NB] = { 0 }, vars_h[VARS_NB] = { 0 };
+
+        av_expr_count_vars(scale->w_pexpr, vars_w, VARS_NB);
+        av_expr_count_vars(scale->h_pexpr, vars_h, VARS_NB);
+
+        if (scale->eval_mode == EVAL_MODE_FRAME &&
+            !frame_changed &&
+            ctx->filter != &ff_vf_scale2ref &&
+            !(vars_w[VAR_N] || vars_w[VAR_T] || vars_w[VAR_POS]) &&
+            !(vars_h[VAR_N] || vars_h[VAR_T] || vars_h[VAR_POS]) &&
+            scale->w && scale->h)
+            goto scale;
 
         if (scale->eval_mode == EVAL_MODE_INIT) {
             snprintf(buf, sizeof(buf)-1, "%d", outlink->w);
             av_opt_set(scale, "w", buf, 0);
             snprintf(buf, sizeof(buf)-1, "%d", outlink->h);
             av_opt_set(scale, "h", buf, 0);
+
+            ret = scale_parse_expr(ctx, NULL, &scale->w_pexpr, "width", scale->w_expr);
+            if (ret < 0)
+                return ret;
+
+            ret = scale_parse_expr(ctx, NULL, &scale->h_pexpr, "height", scale->h_expr);
+            if (ret < 0)
+                return ret;
+        }
+
+        if (ctx->filter == &ff_vf_scale2ref) {
+            scale->var_values[VAR_S2R_MAIN_N] = link->frame_count_out;
+            scale->var_values[VAR_S2R_MAIN_T] = TS2T(in->pts, link->time_base);
+            scale->var_values[VAR_S2R_MAIN_POS] = in->pkt_pos == -1 ? NAN : in->pkt_pos;
+        } else {
+            scale->var_values[VAR_N] = link->frame_count_out;
+            scale->var_values[VAR_T] = TS2T(in->pts, link->time_base);
+            scale->var_values[VAR_POS] = in->pkt_pos == -1 ? NAN : in->pkt_pos;
         }
 
         link->dst->inputs[0]->format = in->format;
@@ -449,6 +718,7 @@ static int scale_frame(AVFilterLink *link, AVFrame *in, AVFrame **frame_out)
             return ret;
     }
 
+scale:
     if (!scale->sws) {
         *frame_out = in;
         return 0;
@@ -555,7 +825,31 @@ static int filter_frame(AVFilterLink *link, AVFrame *in)
 
 static int filter_frame_ref(AVFilterLink *link, AVFrame *in)
 {
+    ScaleContext *scale = link->dst->priv;
     AVFilterLink *outlink = link->dst->outputs[1];
+    int frame_changed;
+
+    frame_changed = in->width  != link->w ||
+                    in->height != link->h ||
+                    in->format != link->format ||
+                    in->sample_aspect_ratio.den != link->sample_aspect_ratio.den ||
+                    in->sample_aspect_ratio.num != link->sample_aspect_ratio.num;
+
+    if (frame_changed) {
+        link->format = in->format;
+        link->w = in->width;
+        link->h = in->height;
+        link->sample_aspect_ratio.num = in->sample_aspect_ratio.num;
+        link->sample_aspect_ratio.den = in->sample_aspect_ratio.den;
+
+        config_props_ref(outlink);
+    }
+
+    if (scale->eval_mode == EVAL_MODE_FRAME) {
+        scale->var_values[VAR_N] = link->frame_count_out;
+        scale->var_values[VAR_T] = TS2T(in->pts, link->time_base);
+        scale->var_values[VAR_POS] = in->pkt_pos == -1 ? NAN : in->pkt_pos;
+    }
 
     return ff_filter_frame(outlink, in);
 }
@@ -564,39 +858,50 @@ static int process_command(AVFilterContext *ctx, const char *cmd, const char *ar
                            char *res, int res_len, int flags)
 {
     ScaleContext *scale = ctx->priv;
-    int ret;
+    char *str_expr;
+    AVExpr **pexpr_ptr;
+    int ret, w, h;
 
-    if (   !strcmp(cmd, "width")  || !strcmp(cmd, "w")
-        || !strcmp(cmd, "height") || !strcmp(cmd, "h")) {
+    w = !strcmp(cmd, "width")  || !strcmp(cmd, "w");
+    h = !strcmp(cmd, "height")  || !strcmp(cmd, "h");
 
-        int old_w = scale->w;
-        int old_h = scale->h;
-        AVFilterLink *outlink = ctx->outputs[0];
+    if (w || h) {
+        str_expr = w ? scale->w_expr : scale->h_expr;
+        pexpr_ptr = w ? &scale->w_pexpr : &scale->h_pexpr;
 
-        av_opt_set(scale, cmd, args, 0);
-        if ((ret = config_props(outlink)) < 0) {
-            scale->w = old_w;
-            scale->h = old_h;
-        }
+        ret = scale_parse_expr(ctx, str_expr, pexpr_ptr, cmd, args);
     } else
         ret = AVERROR(ENOSYS);
 
+    if (ret < 0)
+        av_log(ctx, AV_LOG_ERROR, "Failed to process command. Continuing with existing parameters.\n");
+
     return ret;
 }
 
+#if FF_API_CHILD_CLASS_NEXT
 static const AVClass *child_class_next(const AVClass *prev)
 {
     return prev ? NULL : sws_get_class();
 }
+#endif
+
+static const AVClass *child_class_iterate(void **iter)
+{
+    const AVClass *c = *iter ? NULL : sws_get_class();
+    *iter = (void*)(uintptr_t)c;
+    return c;
+}
 
 #define OFFSET(x) offsetof(ScaleContext, x)
 #define FLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
+#define TFLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_RUNTIME_PARAM
 
 static const AVOption scale_options[] = {
-    { "w",     "Output video width",          OFFSET(w_expr),    AV_OPT_TYPE_STRING,        .flags = FLAGS },
-    { "width", "Output video width",          OFFSET(w_expr),    AV_OPT_TYPE_STRING,        .flags = FLAGS },
-    { "h",     "Output video height",         OFFSET(h_expr),    AV_OPT_TYPE_STRING,        .flags = FLAGS },
-    { "height","Output video height",         OFFSET(h_expr),    AV_OPT_TYPE_STRING,        .flags = FLAGS },
+    { "w",     "Output video width",          OFFSET(w_expr),    AV_OPT_TYPE_STRING,        .flags = TFLAGS },
+    { "width", "Output video width",          OFFSET(w_expr),    AV_OPT_TYPE_STRING,        .flags = TFLAGS },
+    { "h",     "Output video height",         OFFSET(h_expr),    AV_OPT_TYPE_STRING,        .flags = TFLAGS },
+    { "height","Output video height",         OFFSET(h_expr),    AV_OPT_TYPE_STRING,        .flags = TFLAGS },
     { "flags", "Flags to pass to libswscale", OFFSET(flags_str), AV_OPT_TYPE_STRING, { .str = "bilinear" }, .flags = FLAGS },
     { "interl", "set interlacing", OFFSET(interlaced), AV_OPT_TYPE_BOOL, {.i64 = 0 }, -1, 1, FLAGS },
     { "size",   "set video size",          OFFSET(size_str), AV_OPT_TYPE_STRING, {.str = NULL}, 0, FLAGS },
@@ -645,7 +950,10 @@ static const AVClass scale_class = {
     .option           = scale_options,
     .version          = LIBAVUTIL_VERSION_INT,
     .category         = AV_CLASS_CATEGORY_FILTER,
+#if FF_API_CHILD_CLASS_NEXT
     .child_class_next = child_class_next,
+#endif
+    .child_class_iterate = child_class_iterate,
 };
 
 static const AVFilterPad avfilter_vf_scale_inputs[] = {
@@ -685,7 +993,10 @@ static const AVClass scale2ref_class = {
     .option           = scale_options,
     .version          = LIBAVUTIL_VERSION_INT,
     .category         = AV_CLASS_CATEGORY_FILTER,
+#if FF_API_CHILD_CLASS_NEXT
     .child_class_next = child_class_next,
+#endif
+    .child_class_iterate = child_class_iterate,
 };
 
 static const AVFilterPad avfilter_vf_scale2ref_inputs[] = {