Add error handling for frame parallel decode and unit test for that.

Change-Id: I6e309e11f1641618d2424b7a2c0fe744b8974dec

test/invalid_file_test.cc

@@ -97,7 +97,7 @@ const char *const kVP9InvalidFileTests[] = {
   "invalid-vp90-01.webm",
   "invalid-vp90-02.webm",
   "invalid-vp90-2-00-quantizer-00.webm.ivf.s5861_r01-05_b6-.ivf",
-  "invalid-vp90-03.webm",
+  "invalid-vp90-03-v3.webm",
   "invalid-vp90-2-00-quantizer-11.webm.ivf.s52984_r01-05_b6-.ivf",
   "invalid-vp90-2-00-quantizer-11.webm.ivf.s52984_r01-05_b6-z.ivf",
 };

test/test-data.sha1

@@ -4,8 +4,8 @@ fe346136b9b8c1e6f6084cc106485706915795e4  invalid-vp90-01.webm
 25751f5d3b05ff03f0719ad42cd625348eb8961e  invalid-vp90-01.webm.res
 d78e2fceba5ac942246503ec8366f879c4775ca5  invalid-vp90-02.webm
 2dadee5306245fa5eeb0f99652d0e17afbcba96d  invalid-vp90-02.webm.res
-df1a1453feb3c00d7d89746c7003b4163523bff3  invalid-vp90-03.webm
-8fe6fd82bf537340f586f97a7ae31fb37ccda302  invalid-vp90-03.webm.res
+df1a1453feb3c00d7d89746c7003b4163523bff3  invalid-vp90-03-v3.webm
+4935c62becc68c13642a03db1e6d3e2331c1c612  invalid-vp90-03-v3.webm.res
 a432f96ff0a787268e2f94a8092ab161a18d1b06  park_joy_90p_10_420.y4m
 0b194cc312c3a2e84d156a221b0a5eb615dfddc5  park_joy_90p_10_422.y4m
 ff0e0a21dc2adc95b8c1b37902713700655ced17  park_joy_90p_10_444.y4m
@@ -667,3 +667,6 @@ f97088c7359fc8d3d5aa5eafe57bc7308b3ee124  vp90-2-20-big_superframe-01.webm
 7c0ed8d04c4d06c5411dd2e5de2411d37f092db5  vp90-2-20-big_superframe-02.webm.md5
 667ec8718c982aef6be07eb94f083c2efb9d2d16  vp90-2-07-frame_parallel-1.webm
 bfc82bf848e9c05020d61e3ffc1e62f25df81d19  vp90-2-07-frame_parallel-1.webm.md5
+efd5a51d175cfdacd169ed23477729dc558030dc  invalid-vp90-2-07-frame_parallel-1.webm
+9f912712ec418be69adb910e2ca886a63c4cec08  invalid-vp90-2-07-frame_parallel-2.webm
+445f5a53ca9555341852997ccdd480a51540bd14  invalid-vp90-2-07-frame_parallel-3.webm

test/test.mk

@@ -786,14 +786,17 @@ LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-01.webm
 LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-01.webm.res
 LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-02.webm
 LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-02.webm.res
-LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-03.webm
-LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-03.webm.res
+LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-03-v3.webm
+LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-03-v3.webm.res
 LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-2-00-quantizer-00.webm.ivf.s5861_r01-05_b6-.ivf
 LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-2-00-quantizer-00.webm.ivf.s5861_r01-05_b6-.ivf.res
 LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-2-00-quantizer-11.webm.ivf.s52984_r01-05_b6-.ivf
 LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-2-00-quantizer-11.webm.ivf.s52984_r01-05_b6-.ivf.res
 LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-2-00-quantizer-11.webm.ivf.s52984_r01-05_b6-z.ivf
 LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-2-00-quantizer-11.webm.ivf.s52984_r01-05_b6-z.ivf.res
+LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-2-07-frame_parallel-1.webm
+LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-2-07-frame_parallel-2.webm
+LIBVPX_TEST_DATA-$(CONFIG_VP9_DECODER) += invalid-vp90-2-07-frame_parallel-3.webm
 
 ifeq ($(CONFIG_DECODE_PERF_TESTS),yes)
 # BBB VP9 streams

test/vp9_frame_parallel_test.cc

@@ -118,5 +118,91 @@ TEST(VP9MultiThreadedFrameParallel, PauseSeekResume) {
   DecodeFiles(files);
 }
 
+struct InvalidFileList {
+  const char *name;
+  // md5 sum for decoded frames which does not include corrupted frames.
+  const char *expected_md5;
+  // Expected number of decoded frames which does not include corrupted frames.
+  const int expected_frame_count;
+};
+
+// Decodes |filename| with |num_threads|. Return the md5 of the decoded
+// frames which does not include corrupted frames.
+string DecodeInvalidFile(const string &filename, int num_threads,
+                         int expected_frame_count) {
+  libvpx_test::WebMVideoSource video(filename);
+  video.Init();
+
+  vpx_codec_dec_cfg_t cfg = vpx_codec_dec_cfg_t();
+  cfg.threads = num_threads;
+  const vpx_codec_flags_t flags = VPX_CODEC_USE_FRAME_THREADING;
+  libvpx_test::VP9Decoder decoder(cfg, flags, 0);
+
+  libvpx_test::MD5 md5;
+  video.Begin();
+
+  int out_frames = 0;
+  do {
+    const vpx_codec_err_t res =
+        decoder.DecodeFrame(video.cxdata(), video.frame_size());
+    // TODO(hkuang): frame parallel mode should return an error on corruption.
+    if (res != VPX_CODEC_OK) {
+      EXPECT_EQ(VPX_CODEC_OK, res) << decoder.DecodeError();
+      break;
+    }
+
+    video.Next();
+
+    // Flush the decoder at the end of the video.
+    if (!video.cxdata())
+      decoder.DecodeFrame(NULL, 0);
+
+    libvpx_test::DxDataIterator dec_iter = decoder.GetDxData();
+    const vpx_image_t *img;
+
+    // Get decompressed data
+    while ((img = dec_iter.Next())) {
+      ++out_frames;
+      md5.Add(img);
+    }
+  } while (video.cxdata() != NULL);
+
+  EXPECT_EQ(expected_frame_count, out_frames) <<
+      "Input frame count does not match expected output frame count";
+
+  return string(md5.Get());
+}
+
+void DecodeInvalidFiles(const InvalidFileList files[]) {
+  for (const InvalidFileList *iter = files; iter->name != NULL; ++iter) {
+    SCOPED_TRACE(iter->name);
+    for (int t = 2; t <= 8; ++t) {
+      EXPECT_EQ(iter->expected_md5,
+                DecodeInvalidFile(iter->name, t, iter->expected_frame_count))
+          << "threads = " << t;
+    }
+  }
+}
+
+TEST(VP9MultiThreadedFrameParallel, InvalidFileTest) {
+  static const InvalidFileList files[] = {
+    // invalid-vp90-2-07-frame_parallel-1.webm is a 40 frame video file with
+    // one key frame for every ten frames. The 11th frame has corrupted data.
+    { "invalid-vp90-2-07-frame_parallel-1.webm",
+      "0549d0f45f60deaef8eb708e6c0eb6cb", 30},
+    // invalid-vp90-2-07-frame_parallel-2.webm is a 40 frame video file with
+    // one key frame for every ten frames. The 1st and 31st frames have
+    // corrupted data.
+    { "invalid-vp90-2-07-frame_parallel-2.webm",
+      "6a1f3cf6f9e7a364212fadb9580d525e", 20},
+    // invalid-vp90-2-07-frame_parallel-3.webm is a 40 frame video file with
+    // one key frame for every ten frames. The 13th frame has corrupted data.
+    { "invalid-vp90-2-07-frame_parallel-3.webm",
+      "a567c8259d27ad32b1b7f58db5ac89dd", 32},
+    { NULL, NULL, 0},
+  };
+  DecodeInvalidFiles(files);
+}
+
 #endif  // CONFIG_WEBM_IO
 }  // namespace

test/vp9_thread_test.cc

@@ -175,7 +175,7 @@ int Reset(VP9Worker *const /*worker*/) { return 1; }
 int Sync(VP9Worker *const worker) { return !worker->had_error; }
 
 void Execute(VP9Worker *const worker) {
-  worker->had_error |= worker->hook(worker->data1, worker->data2);
+  worker->had_error |= !worker->hook(worker->data1, worker->data2);
 }
 
 void Launch(VP9Worker *const worker) { Execute(worker); }

vp9/decoder/vp9_decodeframe.c

@@ -648,6 +648,7 @@ static void apply_frame_size(VP9_COMMON *cm, int width, int height) {
           cm->subsampling_x, cm->subsampling_y, VP9_DEC_BORDER_IN_PIXELS,
           &pool->frame_bufs[cm->new_fb_idx].raw_frame_buffer, pool->get_fb_cb,
           pool->cb_priv)) {
+    unlock_buffer_pool(pool);
     vpx_internal_error(&cm->error, VPX_CODEC_MEM_ERROR,
                        "Failed to allocate frame buffer");
   }
@@ -1165,6 +1166,10 @@ static size_t read_uncompressed_header(VP9Decoder *pbi,
     }
 
     setup_frame_size(cm, rb);
+    if (pbi->need_resync) {
+      vpx_memset(&cm->ref_frame_map, -1, sizeof(cm->ref_frame_map));
+      pbi->need_resync = 0;
+    }
   } else {
     cm->intra_only = cm->show_frame ? 0 : vp9_rb_read_bit(rb);
 
@@ -1176,6 +1181,10 @@ static size_t read_uncompressed_header(VP9Decoder *pbi,
 
       pbi->refresh_frame_flags = vp9_rb_read_literal(rb, REF_FRAMES);
       setup_frame_size(cm, rb);
+      if (pbi->need_resync) {
+        vpx_memset(&cm->ref_frame_map, -1, sizeof(cm->ref_frame_map));
+        pbi->need_resync = 0;
+      }
     } else {
       pbi->refresh_frame_flags = vp9_rb_read_literal(rb, REF_FRAMES);
       for (i = 0; i < REFS_PER_FRAME; ++i) {
@@ -1203,6 +1212,12 @@ static size_t read_uncompressed_header(VP9Decoder *pbi,
     }
   }
 
+  if (pbi->need_resync) {
+    vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
+                       "Keyframe / intra-only frame required to reset decoder"
+                       " state");
+  }
+
   if (!cm->error_resilient_mode) {
     cm->coding_use_prev_mi = 1;
     cm->refresh_frame_context = vp9_rb_read_bit(rb);
@@ -1239,6 +1254,7 @@ static size_t read_uncompressed_header(VP9Decoder *pbi,
       ++frame_bufs[cm->ref_frame_map[ref_index]].ref_count;
   }
   unlock_buffer_pool(pool);
+  pbi->hold_ref_buf = 1;
 
   if (frame_is_intra_only(cm) || cm->error_resilient_mode)
     vp9_setup_past_independence(cm);
@@ -1457,9 +1473,7 @@ void vp9_decode_frame(VP9Decoder *pbi,
     *p_data_end = decode_tiles(pbi, data + first_partition_size, data_end);
   }
 
-  new_fb->corrupted |= xd->corrupted;
-
-  if (!new_fb->corrupted) {
+  if (!xd->corrupted) {
     if (!cm->error_resilient_mode && !cm->frame_parallel_decoding_mode) {
       vp9_adapt_coef_probs(cm);
 
@@ -1470,6 +1484,9 @@ void vp9_decode_frame(VP9Decoder *pbi,
     } else {
       debug_check_frame_counts(cm);
     }
+  } else {
+    vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
+                       "Decode failed. Frame data is corrupted.");
   }
 
   // Non frame parallel update frame context here.

vp9/decoder/vp9_decoder.c

@@ -58,6 +58,7 @@ VP9Decoder *vp9_decoder_create(BufferPool *const pool) {
   }
 
   cm->error.setjmp = 1;
+  pbi->need_resync = 1;
   initialize_dec();
 
   vp9_rtcd();
@@ -197,16 +198,6 @@ int vp9_get_reference_dec(VP9Decoder *pbi, int index, YV12_BUFFER_CONFIG **fb) {
   return 0;
 }
 
-static INLINE void decrease_ref_count(int idx, RefCntBuffer *const frame_bufs,
-                                      BufferPool *const pool) {
-  if (idx >= 0) {
-    --frame_bufs[idx].ref_count;
-    if (frame_bufs[idx].ref_count == 0) {
-      pool->release_fb_cb(pool->cb_priv, &frame_bufs[idx].raw_frame_buffer);
-    }
-  }
-}
-
 /* If any buffer updating is signaled it should be done here. */
 static void swap_frame_buffers(VP9Decoder *pbi) {
   int ref_index = 0, mask;
@@ -235,7 +226,7 @@ static void swap_frame_buffers(VP9Decoder *pbi) {
     cm->ref_frame_map[ref_index] = cm->next_ref_frame_map[ref_index];
   }
   unlock_buffer_pool(pool);
-
+  pbi->hold_ref_buf = 0;
   cm->frame_to_show = get_frame_new_buffer(cm);
 
   if (!pbi->frame_parallel_decode || !cm->show_frame) {
@@ -256,7 +247,6 @@ int vp9_receive_compressed_data(VP9Decoder *pbi,
   RefCntBuffer *const frame_bufs = cm->buffer_pool->frame_bufs;
   const uint8_t *source = *psource;
   int retcode = 0;
-
   cm->error.error_code = VPX_CODEC_OK;
 
   if (size == 0) {
@@ -282,7 +272,7 @@ int vp9_receive_compressed_data(VP9Decoder *pbi,
                         &frame_bufs[cm->new_fb_idx].raw_frame_buffer);
   cm->new_fb_idx = get_free_fb(cm);
 
-
+  pbi->hold_ref_buf = 0;
   if (pbi->frame_parallel_decode) {
     VP9Worker *const worker = pbi->frame_worker_owner;
     vp9_frameworker_lock_stats(worker);
@@ -300,18 +290,35 @@ int vp9_receive_compressed_data(VP9Decoder *pbi,
     cm->error.setjmp = 0;
     pbi->ready_for_new_data = 1;
 
-    // We do not know if the missing frame(s) was supposed to update
-    // any of the reference buffers, but we act conservative and
-    // mark only the last buffer as corrupted.
-    //
-    // TODO(jkoleszar): Error concealment is undefined and non-normative
-    // at this point, but if it becomes so, [0] may not always be the correct
-    // thing to do here.
-    if (cm->frame_refs[0].idx != INT_MAX && cm->frame_refs[0].buf != NULL)
-      cm->frame_refs[0].buf->corrupted = 1;
-
-    if (frame_bufs[cm->new_fb_idx].ref_count > 0)
-      --frame_bufs[cm->new_fb_idx].ref_count;
+    lock_buffer_pool(pool);
+    // Release all the reference buffers if worker thread is holding them.
+    if (pbi->hold_ref_buf == 1) {
+      int ref_index = 0, mask;
+      VP9_COMMON *const cm = &pbi->common;
+      BufferPool *const pool = cm->buffer_pool;
+      RefCntBuffer *const frame_bufs = cm->buffer_pool->frame_bufs;
+      for (mask = pbi->refresh_frame_flags; mask; mask >>= 1) {
+        const int old_idx = cm->ref_frame_map[ref_index];
+        // Current thread releases the holding of reference frame.
+        decrease_ref_count(old_idx, frame_bufs, pool);
+
+        // Release the reference frame in reference map.
+        if ((mask & 1) && old_idx >= 0) {
+          decrease_ref_count(old_idx, frame_bufs, pool);
+        }
+        ++ref_index;
+      }
+
+      // Current thread releases the holding of reference frame.
+      for (; ref_index < REF_FRAMES && !cm->show_existing_frame; ++ref_index) {
+        const int old_idx = cm->ref_frame_map[ref_index];
+        decrease_ref_count(old_idx, frame_bufs, pool);
+      }
+      pbi->hold_ref_buf = 0;
+    }
+    // Release current frame.
+    decrease_ref_count(cm->new_fb_idx, frame_bufs, pool);
+    unlock_buffer_pool(pool);
 
     return -1;
   }

vp9/decoder/vp9_decoder.h

@@ -65,6 +65,8 @@ typedef struct VP9Decoder {
 
   int max_threads;
   int inv_tile_order;
+  int need_resync;  // wait for key/intra-only frame.
+  int hold_ref_buf;  // hold the reference buffer.
 } VP9Decoder;
 
 int vp9_receive_compressed_data(struct VP9Decoder *pbi,
@@ -88,6 +90,21 @@ struct VP9Decoder *vp9_decoder_create(BufferPool *const pool);
 
 void vp9_decoder_remove(struct VP9Decoder *pbi);
 
+static INLINE void decrease_ref_count(int idx, RefCntBuffer *const frame_bufs,
+                                      BufferPool *const pool) {
+  if (idx >= 0) {
+    --frame_bufs[idx].ref_count;
+    // A worker may only get a free framebuffer index when calling get_free_fb.
+    // But the private buffer is not set up until finish decoding header.
+    // So any error happens during decoding header, the frame_bufs will not
+    // have valid priv buffer.
+    if (frame_bufs[idx].ref_count == 0 &&
+        frame_bufs[idx].raw_frame_buffer.priv) {
+      pool->release_fb_cb(pool->cb_priv, &frame_bufs[idx].raw_frame_buffer);
+    }
+  }
+}
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif

vp9/decoder/vp9_dthread.c

@@ -320,7 +320,7 @@ void vp9_frameworker_wait(VP9Worker *const worker, RefCntBuffer *const ref_buf,
 
   // Enabling the following line of code will get harmless tsan error but
   // will get best performance.
-  // if (ref_buf->row >= row) return;
+  // if (ref_buf->row >= row && ref_buf->buf.corrupted != 1) return;
 
   {
     // Find the worker thread that owns the reference frame. If the reference
@@ -340,10 +340,19 @@ void vp9_frameworker_wait(VP9Worker *const worker, RefCntBuffer *const ref_buf,
 #endif
 
     vp9_frameworker_lock_stats(ref_worker);
-    while (ref_buf->row < row && pbi->cur_buf == ref_buf) {
+    while (ref_buf->row < row && pbi->cur_buf == ref_buf &&
+           ref_buf->buf.corrupted != 1) {
       pthread_cond_wait(&ref_worker_data->stats_cond,
                         &ref_worker_data->stats_mutex);
     }
+
+    if (ref_buf->buf.corrupted == 1) {
+      FrameWorkerData *const worker_data = (FrameWorkerData *)worker->data1;
+      vp9_frameworker_unlock_stats(ref_worker);
+      vpx_internal_error(&worker_data->pbi->common.error,
+                         VPX_CODEC_CORRUPT_FRAME,
+                         "Worker %p failed to decode frame", worker);
+    }
     vp9_frameworker_unlock_stats(ref_worker);
   }
 #else
@@ -358,8 +367,11 @@ void vp9_frameworker_broadcast(RefCntBuffer *const buf, int row) {
   VP9Worker *worker = buf->frame_worker_owner;
 
 #ifdef DEBUG_THREAD
-  printf("%d %p worker decode to (%d) \r\n", worker_data->worker_id,
-         buf->frame_worker_owner, row);
+  {
+    FrameWorkerData *const worker_data = (FrameWorkerData *)worker->data1;
+    printf("%d %p worker decode to (%d) \r\n", worker_data->worker_id,
+           buf->frame_worker_owner, row);
+  }
 #endif
 
   vp9_frameworker_lock_stats(worker);
@@ -403,7 +415,7 @@ void vp9_frameworker_copy_context(VP9Worker *const dst_worker,
     dst_cm->prev_mi_grid_visible = src_cm->mi_grid_visible;
     dst_cm->last_frame_seg_map = src_cm->current_frame_seg_map;
   }
-
+  dst_worker_data->pbi->need_resync = src_worker_data->pbi->need_resync;
   vp9_frameworker_unlock_stats(src_worker);
 
   dst_worker_data->pbi->prev_buf =

vp9/vp9_dx_iface.c

@@ -290,11 +290,37 @@ static int frame_worker_hook(void *arg1, void *arg2) {
   FrameWorkerData *const frame_worker_data = (FrameWorkerData *)arg1;
   const uint8_t *data = frame_worker_data->data;
   (void)arg2;
+
   frame_worker_data->result =
       vp9_receive_compressed_data(frame_worker_data->pbi,
                                   frame_worker_data->data_size,
                                   &data);
   frame_worker_data->data_end = data;
+
+  if (frame_worker_data->pbi->frame_parallel_decode) {
+    // In frame parallel decoding, a worker thread must successfully decode all
+    // the compressed data.
+    if (frame_worker_data->result != 0 ||
+        frame_worker_data->data + frame_worker_data->data_size - 1 > data) {
+      VP9Worker *const worker = frame_worker_data->pbi->frame_worker_owner;
+      BufferPool *const pool = frame_worker_data->pbi->common.buffer_pool;
+      // Signal all the other threads that are waiting for this frame.
+      vp9_frameworker_lock_stats(worker);
+      frame_worker_data->frame_context_ready = 1;
+      lock_buffer_pool(pool);
+      frame_worker_data->pbi->cur_buf->buf.corrupted = 1;
+      unlock_buffer_pool(pool);
+      frame_worker_data->pbi->need_resync = 1;
+      vp9_frameworker_signal_stats(worker);
+      vp9_frameworker_unlock_stats(worker);
+      return 0;
+    }
+  } else if (frame_worker_data->result != 0) {
+    // Check decode result in serial decode.
+    frame_worker_data->pbi->cur_buf->buf.corrupted = 1;
+    frame_worker_data->pbi->need_resync = 1;
+  }
+
   return !frame_worker_data->result;
 }
 
@@ -444,7 +470,6 @@ static vpx_codec_err_t decode_one(vpx_codec_alg_priv_t *ctx,
           &ctx->frame_workers[ctx->last_submit_worker_id]);
 
     frame_worker_data->pbi->ready_for_new_data = 0;
-
     // Copy the compressed data into worker's internal buffer.
     // TODO(hkuang): Will all the workers allocate the same size
     // as the size of the first intra frame be better? This will
@@ -474,6 +499,7 @@ static vpx_codec_err_t decode_one(vpx_codec_alg_priv_t *ctx,
         (ctx->next_submit_worker_id + 1) % ctx->num_frame_workers;
 
     --ctx->available_threads;
+    worker->had_error = 0;
     winterface->launch(worker);
   }
 
@@ -714,11 +740,7 @@ static void release_last_output_frame(vpx_codec_alg_priv_t *ctx) {
   if (ctx->frame_parallel_decode && ctx->last_show_frame >= 0) {
     BufferPool *const pool = ctx->buffer_pool;
     lock_buffer_pool(pool);
-    --frame_bufs[ctx->last_show_frame].ref_count;
-    if (frame_bufs[ctx->last_show_frame].ref_count == 0) {
-      pool->release_fb_cb(pool->cb_priv,
-                          &frame_bufs[ctx->last_show_frame].raw_frame_buffer);
-    }
+    decrease_ref_count(ctx->last_show_frame, frame_bufs, pool);
     unlock_buffer_pool(pool);
   }
 }
@@ -758,8 +780,12 @@ static vpx_image_t *decoder_get_frame(vpx_codec_alg_priv_t *ctx,
       ctx->next_output_worker_id =
           (ctx->next_output_worker_id + 1) % ctx->num_frame_workers;
       // Wait for the frame from worker thread.
-      winterface->sync(worker);
-      if (vp9_get_raw_frame(frame_worker_data->pbi, &sd, &flags) == 0) {
+      if (!winterface->sync(worker)) {
+        // Decoding failed. Release the worker thread.
+        ++ctx->available_threads;
+        if (ctx->flushed != 1)
+          return img;
+      } else if (vp9_get_raw_frame(frame_worker_data->pbi, &sd, &flags) == 0) {
         VP9_COMMON *const cm = &frame_worker_data->pbi->common;
         RefCntBuffer *const frame_bufs = cm->buffer_pool->frame_bufs;
         ++ctx->available_threads;

vpx/vpx_frame_buffer.h

@@ -26,7 +26,7 @@ extern "C" {
  *  Each thread will use one work buffer.
  * TODO(hkuang): Add support to set number of worker threads dynamically.
  */
-#define VPX_MAXIMUM_WORK_BUFFERS 4
+#define VPX_MAXIMUM_WORK_BUFFERS 8
 
 /*!\brief The maximum number of reference buffers that a VP9 encoder may use.
  */