Implement interlaced scaling.

Fixes issue2632 if interl=1 is used or the automatic interlace detection is enabled
and works. This has the advantage compared to the patch in issue2632 that it causes
no speed loss and it also works when scaling is used. The disadvantage is that
interlacing autodetection does not yet work very well it seems.
This is the same method mplayer uses

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/vf_scale.c

@@ -25,10 +25,12 @@
 
 #include "avfilter.h"
 #include "libavutil/pixdesc.h"
+#include "libavutil/avassert.h"
 #include "libswscale/swscale.h"
 
 typedef struct {
     struct SwsContext *sws;     ///< software scaler context
+    struct SwsContext *isws[2]; ///< software scaler context for interlaced material
 
     /**
      * New dimensions. Special values are:
@@ -41,6 +43,7 @@ typedef struct {
     int hsub, vsub;             ///< chroma subsampling
     int slice_y;                ///< top of current output slice
     int input_is_pal;           ///< set to 1 if the input format is paletted
+    int interlaced;
 } ScaleContext;
 
 static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
@@ -53,6 +56,10 @@ static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
         sscanf(args, "%d:%d", &scale->w, &scale->h);
         p = strstr(args,"flags=");
         if (p) scale->flags = strtoul(p+6, NULL, 0);
+        if(strstr(args,"interl=1")){
+            scale->interlaced=1;
+        }else if(strstr(args,"interl=-1"))
+            scale->interlaced=-1;
     }
 
     /* sanity check params */
@@ -70,6 +77,8 @@ static av_cold void uninit(AVFilterContext *ctx)
 {
     ScaleContext *scale = ctx->priv;
     sws_freeContext(scale->sws);
+    sws_freeContext(scale->isws[0]);
+    sws_freeContext(scale->isws[1]);
     scale->sws = NULL;
 }
 
@@ -138,6 +147,12 @@ static int config_props(AVFilterLink *outlink)
     scale->sws = sws_getContext(inlink ->w, inlink ->h, inlink ->format,
                                 outlink->w, outlink->h, outlink->format,
                                 scale->flags, NULL, NULL, NULL);
+    scale->isws[0] = sws_getContext(inlink ->w, inlink ->h/2, inlink ->format,
+                                    outlink->w, outlink->h/2, outlink->format,
+                                    scale->flags, NULL, NULL, NULL);
+    scale->isws[1] = sws_getContext(inlink ->w, inlink ->h/2, inlink ->format,
+                                    outlink->w, outlink->h/2, outlink->format,
+                                    scale->flags, NULL, NULL, NULL);
     if (!scale->sws)
         return AVERROR(EINVAL);
 
@@ -169,26 +184,46 @@ static void start_frame(AVFilterLink *link, AVFilterBufferRef *picref)
     avfilter_start_frame(outlink, avfilter_ref_buffer(outpicref, ~0));
 }
 
+static int scale_slice(AVFilterLink *link, struct SwsContext *sws, int y, int h, int mul, int field)
+{
+    ScaleContext *scale = link->dst->priv;
+    AVFilterBufferRef *cur_pic = link->cur_buf;
+    AVFilterBufferRef *out_buf = link->dst->outputs[0]->out_buf;
+    const uint8_t *in[4], *out[4];
+    int in_stride[4],out_stride[4];
+    int i;
+
+    for(i=0; i<4; i++){
+        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];
+    }
+    if(scale->input_is_pal){
+         in[1] = cur_pic->data[1];
+        out[1] = out_buf->data[1];
+    }
+
+    return sws_scale(sws, in, in_stride, y/mul, h,
+                         out,out_stride);
+}
+
 static void draw_slice(AVFilterLink *link, int y, int h, int slice_dir)
 {
     ScaleContext *scale = link->dst->priv;
     int out_h;
-    AVFilterBufferRef *cur_pic = link->cur_buf;
-    const uint8_t *data[4];
 
     if (scale->slice_y == 0 && slice_dir == -1)
         scale->slice_y = link->dst->outputs[0]->h;
 
-    data[0] = cur_pic->data[0] +  y               * cur_pic->linesize[0];
-    data[1] = scale->input_is_pal ?
-              cur_pic->data[1] :
-              cur_pic->data[1] + (y>>scale->vsub) * cur_pic->linesize[1];
-    data[2] = cur_pic->data[2] + (y>>scale->vsub) * cur_pic->linesize[2];
-    data[3] = cur_pic->data[3] +  y               * cur_pic->linesize[3];
-
-    out_h = sws_scale(scale->sws, data, cur_pic->linesize, y, h,
-                      link->dst->outputs[0]->out_buf->data,
-                      link->dst->outputs[0]->out_buf->linesize);
+    if(scale->interlaced>0 || (scale->interlaced<0 && link->cur_buf->video->interlaced)){
+        av_assert0(y%4 == 0);
+        out_h = scale_slice(link, scale->isws[0], y, (h+1)/2, 2, 0);
+        out_h+= scale_slice(link, scale->isws[1], y,  h   /2, 2, 1);
+    }else{
+        out_h = scale_slice(link, scale->sws, y, h, 1, 0);
+    }
 
     if (slice_dir == -1)
         scale->slice_y -= out_h;