[FFmpeg-devel] [PATCH] ffmpeg: set extra_hw_frames to account for frames held in queues

[Mark Thompson]

Since e0da916b8f5b079a4865eef7f64863f50785463d the ffmpeg utility has
held multiple frames output by the decoder in internal queues without
telling the decoder that it is going to do so.  When the decoder has a
fixed-size pool of frames (common in some hardware APIs where the output
frames must be stored as an array texture) this could lead to the pool
being exhausted and the decoder getting stuck.  Fix this by telling the
decoder to allocate additional frames according to the queue size.
---
  fftools/ffmpeg_dec.c   | 13 +++++++++++++
  fftools/ffmpeg_sched.c | 11 ++++++++++-
  fftools/ffmpeg_sched.h |  7 +++++++
  3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/fftools/ffmpeg_dec.c b/fftools/ffmpeg_dec.c
index 8c92b27cc1..0dab989cdd 100644
--- a/fftools/ffmpeg_dec.c
+++ b/fftools/ffmpeg_dec.c
@@ -1146,6 +1146,19 @@ int dec_open(Decoder **pdec, Scheduler *sch,
          goto fail;
      }

+    if (dp->dec_ctx->hw_device_ctx) {
+        // Update decoder extra_hw_frames option to account for the
+        // frames held in queues inside the ffmpeg utility.  This is
+        // called after avcodec_open2() because the user-set value of
+        // extra_hw_frames becomes valid in there, and we need to add
+        // this on top of it.
+        int extra_frames = DEFAULT_THREAD_QUEUE_SIZE;
+        if (dp->dec_ctx->extra_hw_frames >= 0)
+            dp->dec_ctx->extra_hw_frames += extra_frames;
+        else
+            dp->dec_ctx->extra_hw_frames = extra_frames;
+    }
+
      ret = check_avoptions(*dec_opts);
      if (ret < 0)
          goto fail;
diff --git a/fftools/ffmpeg_sched.c b/fftools/ffmpeg_sched.c
index 1144fce958..9ff9431270 100644
--- a/fftools/ffmpeg_sched.c
+++ b/fftools/ffmpeg_sched.c
@@ -361,7 +361,16 @@ static int queue_alloc(ThreadQueue **ptq, unsigned nb_streams, unsigned queue_si
      ThreadQueue *tq;
      ObjPool *op;

-    queue_size = queue_size > 0 ? queue_size : 8;
+    queue_size = queue_size > 0 ? queue_size : DEFAULT_THREAD_QUEUE_SIZE;
+
+    if (type == QUEUE_FRAMES) {
+        // This queue length is used in the decoder code to ensure that
+        // there are enough entries in fixed-size frame pools to account
+        // for frames held in queues inside the ffmpeg utility.  If this
+        // can ever dynamically change then the corresponding decode
+        // code needs to be updated as well.
+        av_assert0(queue_size == DEFAULT_THREAD_QUEUE_SIZE);
+    }

      op = (type == QUEUE_PACKETS) ? objpool_alloc_packets() :
                                     objpool_alloc_frames();
diff --git a/fftools/ffmpeg_sched.h b/fftools/ffmpeg_sched.h
index 95f9c1d4db..315053ae42 100644
--- a/fftools/ffmpeg_sched.h
+++ b/fftools/ffmpeg_sched.h
@@ -233,6 +233,13 @@ int sch_add_filtergraph(Scheduler *sch, unsigned nb_inputs, unsigned nb_outputs,
   */
  int sch_add_mux(Scheduler *sch, SchThreadFunc func, int (*init)(void *),
                  void *ctx, int sdp_auto, unsigned thread_queue_size);
+
+/**
+ * Default size of a thread queue, used if thread_queue_size is not set on a
+ * call to sch_add_mux().
+ */
+#define DEFAULT_THREAD_QUEUE_SIZE 8
+
  /**
   * Add a muxed stream for a previously added muxer.
   *
-- 
2.43.0