avfilter/vf_tinterlace: use frame counter from lavfi

Remove internal counter.

libavfilter/tinterlace.h

@@ -67,7 +67,6 @@ typedef struct TInterlaceContext {
     AVRational preout_time_base;
     int flags;                  ///< flags affecting interlacing algorithm
     int lowpass;                ///< legacy interlace filter lowpass mode
-    int frame;                  ///< number of the output frame
     int vsub;                   ///< chroma vertical subsampling
     AVFrame *cur;
     AVFrame *next;

libavfilter/vf_tinterlace.c

@@ -423,7 +423,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *picref)
         out->height = outlink->h;
         out->sample_aspect_ratio = av_mul_q(cur->sample_aspect_ratio, av_make_q(2, 1));
 
-        field = (1 + tinterlace->frame) & 1 ? FIELD_UPPER : FIELD_LOWER;
+        field = (1 + outlink->frame_count_in) & 1 ? FIELD_UPPER : FIELD_LOWER;
         /* copy upper and lower fields */
         copy_picture_field(tinterlace, out->data, out->linesize,
                            (const uint8_t **)cur->data, cur->linesize,
@@ -517,7 +517,6 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *picref)
 
     out->pts = av_rescale_q(out->pts, tinterlace->preout_time_base, outlink->time_base);
     ret = ff_filter_frame(outlink, out);
-    tinterlace->frame++;
 
     return ret;
 }