lavfi: make ff_framequeue_skip_samples() more useful.

Instead of just updating statistics and leaving the work to the
call site, have it actually do the work.

Also: skip the samples by updating the frame data pointers
instead of moving the samples. More efficient and avoid writing
into shared frames.
Found-By: Muhammad Faiz <mfcc64@gmail.com>

libavfilter/avfilter.c

@@ -1235,13 +1235,7 @@ static int take_samples(AVFilterLink *link, unsigned min, unsigned max,
         frame = ff_framequeue_peek(&link->fifo, 0);
         av_samples_copy(buf->extended_data, frame->extended_data, p, 0, n,
                         link->channels, link->format);
-        frame->nb_samples -= n;
-        av_samples_copy(frame->extended_data, frame->extended_data, 0, n,
-                        frame->nb_samples, link->channels, link->format);
-        if (frame->pts != AV_NOPTS_VALUE)
-            frame->pts += av_rescale_q(n, av_make_q(1, link->sample_rate), link->time_base);
-        ff_framequeue_update_peeked(&link->fifo, 0);
-        ff_framequeue_skip_samples(&link->fifo, n);
+        ff_framequeue_skip_samples(&link->fifo, n, link->time_base);
     }
 
     *rframe = buf;

libavfilter/framequeue.c

@@ -121,3 +121,30 @@ AVFrame *ff_framequeue_peek(FFFrameQueue *fq, size_t idx)
     check_consistency(fq);
     return b->frame;
 }
+
+void ff_framequeue_skip_samples(FFFrameQueue *fq, size_t samples, AVRational time_base)
+{
+    FFFrameBucket *b;
+    size_t bytes;
+    int planar, planes, i;
+
+    check_consistency(fq);
+    av_assert1(fq->queued);
+    b = bucket(fq, 0);
+    av_assert1(samples < b->frame->nb_samples);
+    planar = av_sample_fmt_is_planar(b->frame->format);
+    planes = planar ? b->frame->channels : 1;
+    bytes = samples * av_get_bytes_per_sample(b->frame->format);
+    if (!planar)
+        bytes *= b->frame->channels;
+    if (b->frame->pts != AV_NOPTS_VALUE)
+        b->frame->pts += av_rescale_q(samples, av_make_q(1, b->frame->sample_rate), time_base);
+    b->frame->nb_samples -= samples;
+    b->frame->linesize[0] -= bytes;
+    for (i = 0; i < planes; i++)
+        b->frame->extended_data[i] += bytes;
+    for (i = 0; i < planes && i < AV_NUM_DATA_POINTERS; i++)
+        b->frame->data[i] = b->frame->extended_data[i];
+    fq->total_samples_tail += samples;
+    ff_framequeue_update_peeked(fq, 0);
+}

libavfilter/framequeue.h

@@ -161,14 +161,13 @@ static inline void ff_framequeue_update_peeked(FFFrameQueue *fq, size_t idx)
 }
 
 /**
- * Update the sample count in the queue.
+ * Skip samples from the first frame in the queue.
  *
  * This function must be used when the first frame was accessed using
- * ff_framequeue_peek() and samples were removed from it.
+ * ff_framequeue_peek() and samples were consumed from it.
+ * It adapts the data pointers and timestamps of the head frame to account
+ * for the skipped samples.
  */
-static inline void ff_framequeue_skip_samples(FFFrameQueue *fq, size_t n)
-{
-    fq->total_samples_tail += n;
-}
+void ff_framequeue_skip_samples(FFFrameQueue *fq, size_t samples, AVRational time_base);
 
 #endif /* AVFILTER_FRAMEQUEUE_H */