[FFmpeg-devel] [PATCH v2] avfilter: take_samples: do not directly return frame when samples are skipped

[Muhammad Faiz]

Modifying data pointer when skipping samples may make it unaligned.
Workaround for Ticket6349.

This should fix the crash of ticket's testcase and a crash/regression
with avxsynth (reported by Michael Niedermayer).

Also change frame->nb_samples < max to frame->nb_samples <= max.
This improves performance. Benchmark:
./ffmpeg -filter_complex "aevalsrc=0:n=1166,firequalizer=fixed=on" -f null null
old:
  25767 decicycles in take_samples,    1023 runs,      1 skips
  25422 decicycles in take_samples,    2047 runs,      1 skips
  25181 decicycles in take_samples,    4095 runs,      1 skips
  24904 decicycles in take_samples,    8191 runs,      1 skips

new:
    550 decicycles in take_samples,    1024 runs,      0 skips
    548 decicycles in take_samples,    2048 runs,      0 skips
    545 decicycles in take_samples,    4096 runs,      0 skips
    544 decicycles in take_samples,    8192 runs,      0 skips

Signed-off-by: Muhammad Faiz <mfcc64 at gmail.com>
---
 libavfilter/avfilter.c   | 8 +++++++-
 libavfilter/framequeue.c | 2 ++
 libavfilter/framequeue.h | 5 +++++
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/libavfilter/avfilter.c b/libavfilter/avfilter.c
index 08b86b0..e60b024 100644
--- a/libavfilter/avfilter.c
+++ b/libavfilter/avfilter.c
@@ -1191,7 +1191,7 @@ static int take_samples(AVFilterLink *link, unsigned min, unsigned max,
        called with enough samples. */
     av_assert1(samples_ready(link, link->min_samples));
     frame0 = frame = ff_framequeue_peek(&link->fifo, 0);
-    if (frame->nb_samples >= min && frame->nb_samples < max) {
+    if (!link->fifo.samples_skipped && frame->nb_samples >= min && frame->nb_samples <= max) {
         *rframe = ff_framequeue_take(&link->fifo);
         return 0;
     }
@@ -1522,6 +1522,12 @@ int ff_inlink_consume_frame(AVFilterLink *link, AVFrame **rframe)
     *rframe = NULL;
     if (!ff_inlink_check_available_frame(link))
         return 0;
+
+    if (link->fifo.samples_skipped) {
+        frame = ff_framequeue_peek(&link->fifo, 0);
+        return ff_inlink_consume_samples(link, frame->nb_samples, frame->nb_samples, rframe);
+    }
+
     frame = ff_framequeue_take(&link->fifo);
     consume_update(link, frame);
     *rframe = frame;
diff --git a/libavfilter/framequeue.c b/libavfilter/framequeue.c
index 26bfa49..fed1118 100644
--- a/libavfilter/framequeue.c
+++ b/libavfilter/framequeue.c
@@ -107,6 +107,7 @@ AVFrame *ff_framequeue_take(FFFrameQueue *fq)
     fq->tail &= fq->allocated - 1;
     fq->total_frames_tail++;
     fq->total_samples_tail += b->frame->nb_samples;
+    fq->samples_skipped = 0;
     check_consistency(fq);
     return b->frame;
 }
@@ -146,5 +147,6 @@ void ff_framequeue_skip_samples(FFFrameQueue *fq, size_t samples, AVRational tim
     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;
+    fq->samples_skipped = 1;
     ff_framequeue_update_peeked(fq, 0);
 }
diff --git a/libavfilter/framequeue.h b/libavfilter/framequeue.h
index 5aa2c72..c49d872 100644
--- a/libavfilter/framequeue.h
+++ b/libavfilter/framequeue.h
@@ -100,6 +100,11 @@ typedef struct FFFrameQueue {
      */
     uint64_t total_samples_tail;
 
+    /**
+     * Indicate that samples are skipped
+     */
+    int samples_skipped;
+
 } FFFrameQueue;
 
 /**
-- 
2.9.3