[FFmpeg-devel] [PATCH] avfilter/scale_vaapi: add support for basic height/width expressions

[Aman Gupta]

From: Aman Gupta <aman at tmm1.net>

Copied directly from vf_scale.c.

Implements the same expression logic, however not all the variables were copied over.
This patch was sufficient for my particular use-case `scale_vaapi=-2:min(ih\,720)`,
but perhaps it makes sense to add support for the remaining variables
and pull out shared code into a new vf_scale_common.c?
---
 libavfilter/vf_scale_vaapi.c | 98 ++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 95 insertions(+), 3 deletions(-)

diff --git a/libavfilter/vf_scale_vaapi.c b/libavfilter/vf_scale_vaapi.c
index d1cb246..0d1e1b3 100644
--- a/libavfilter/vf_scale_vaapi.c
+++ b/libavfilter/vf_scale_vaapi.c
@@ -22,6 +22,7 @@
 #include <va/va_vpp.h>
 
 #include "libavutil/avassert.h"
+#include "libavutil/eval.h"
 #include "libavutil/hwcontext.h"
 #include "libavutil/hwcontext_vaapi.h"
 #include "libavutil/mem.h"
@@ -32,6 +33,22 @@
 #include "formats.h"
 #include "internal.h"
 
+static const char *const var_names[] = {
+    "in_w",   "iw",
+    "in_h",   "ih",
+    "out_w",  "ow",
+    "out_h",  "oh",
+    NULL
+};
+
+enum var_name {
+    VAR_IN_W,   VAR_IW,
+    VAR_IN_H,   VAR_IH,
+    VAR_OUT_W,  VAR_OW,
+    VAR_OUT_H,  VAR_OH,
+    VARS_NB
+};
+
 typedef struct ScaleVAAPIContext {
     const AVClass *class;
 
@@ -50,9 +67,21 @@ typedef struct ScaleVAAPIContext {
 
     char *output_format_string;
     enum AVPixelFormat output_format;
+
+    /**
+     * New dimensions. Special values are:
+     *   0 = original width/height
+     *  -1 = keep original aspect
+     *  -N = try to keep aspect but make sure it is divisible by N
+     */
+    int w, h;
+
+    char *w_expr;               ///< width  expression string
+    char *h_expr;               ///< height expression string
+
+    /* computed width/height */
     int output_width;
     int output_height;
-
 } ScaleVAAPIContext;
 
 
@@ -118,6 +147,14 @@ static int scale_vaapi_config_output(AVFilterLink *outlink)
     VAStatus vas;
     int err, i;
 
+    AVFilterLink *inlink = outlink->src->inputs[0];
+    ScaleVAAPIContext *scale = ctx;
+    int64_t w, h;
+    double var_values[VARS_NB], res;
+    char *expr;
+    int ret;
+    int factor_w, factor_h;
+
     scale_vaapi_pipeline_uninit(ctx);
 
     ctx->device_ref = av_buffer_ref(ctx->input_frames->device_ref);
@@ -162,6 +199,61 @@ static int scale_vaapi_config_output(AVFilterLink *outlink)
         }
     }
 
+    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;
+
+    /* 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;
+
+    ctx->output_width = w;
+    ctx->output_height = h;
+
     if (ctx->output_width  < constraints->min_width  ||
         ctx->output_height < constraints->min_height ||
         ctx->output_width  > constraints->max_width  ||
@@ -414,9 +506,9 @@ 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, .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, .flags = FLAGS },
     { "format", "Output video format (software format of hardware frames)",
       OFFSET(output_format_string), AV_OPT_TYPE_STRING, .flags = FLAGS },
     { NULL },
-- 
2.10.1 (Apple Git-78)