@@ -80,21 +80,35 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)

     AVFilterContext   *ctx     = inlink->dst;

     FieldOrderContext *s       = ctx->priv;

     AVFilterLink      *outlink = ctx->outputs[0];

-    int h, plane, line_step, line_size, line;

-    uint8_t *data;

+    int h, plane, src_line_step, dst_line_step, line_size, line;

+    uint8_t *dst, *src;

+    AVFrame *out;

     if (!frame->interlaced_frame ||

         frame->top_field_first == s->dst_tff)

         return ff_filter_frame(outlink, frame);

+    if (av_frame_is_writable(frame)) {

+        out = frame;

+    } else {

+        out = ff_get_video_buffer(outlink, outlink->w, outlink->h);

+        if (!out) {

+            av_frame_free(&frame);

+            return AVERROR(ENOMEM);

+        }

+        av_frame_copy_props(out, frame);

+    }

+

     av_dlog(ctx,

             "picture will move %s one line\n",

             s->dst_tff ? "up" : "down");

     h = frame->height;

     for (plane = 0; plane < 4 && frame->data[plane] && frame->linesize[plane]; plane++) {

-        line_step = frame->linesize[plane];

+        dst_line_step = out->linesize[plane];

+        src_line_step = frame->linesize[plane];

         line_size = s->line_size[plane];

-        data = frame->data[plane];

+        dst = out->data[plane];

+        src = frame->data[plane];

         if (s->dst_tff) {

             /** Move every line up one line, working from

              *  the top to the bottom of the frame.

@@ -103,11 +117,12 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)

              *  penultimate line from that field. */

             for (line = 0; line < h; line++) {

                 if (1 + line < frame->height) {

-                    memcpy(data, data + line_step, line_size);

+                    memcpy(dst, src + src_line_step, line_size);

                 } else {

-                    memcpy(data, data - line_step - line_step, line_size);

+                    memcpy(dst, src - 2 * src_line_step, line_size);

                 }

-                data += line_step;

+                dst += dst_line_step;

+                src += src_line_step;

             }

         } else {

             /** Move every line down one line, working from

@@ -115,20 +130,24 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)

              *  The original bottom line is lost.

              *  The new first line is created as a copy of the

              *  second line from that field. */

-            data += (h - 1) * line_step;

+            dst += (h - 1) * dst_line_step;

+            src += (h - 1) * src_line_step;

             for (line = h - 1; line >= 0 ; line--) {

                 if (line > 0) {

-                    memcpy(data, data - line_step, line_size);

+                    memcpy(dst, src - src_line_step, line_size);

                 } else {

-                    memcpy(data, data + line_step + line_step, line_size);

+                    memcpy(dst, src + 2 * src_line_step, line_size);

                 }

-                data -= line_step;

+                dst -= dst_line_step;

+                src -= src_line_step;

             }

         }

     }

-    frame->top_field_first = s->dst_tff;

+    out->top_field_first = s->dst_tff;

-    return ff_filter_frame(outlink, frame);

+    if (frame != out)

+        av_frame_free(&frame);

+    return ff_filter_frame(outlink, out);

 }

 #define OFFSET(x) offsetof(FieldOrderContext, x)

@@ -149,7 +168,6 @@ static const AVFilterPad avfilter_vf_fieldorder_inputs[] = {

         .type             = AVMEDIA_TYPE_VIDEO,

         .config_props     = config_input,

         .filter_frame     = filter_frame,

-        .needs_writable   = 1,

     },

     { NULL }

 };