diff --git a/aos/BUILD b/aos/BUILD
index 2ae0fec..f0c12b9 100644
--- a/aos/BUILD
+++ b/aos/BUILD
@@ -463,6 +463,7 @@
         "@com_github_google_glog//:glog",
         "@com_google_absl//absl/strings",
         "@com_google_absl//absl/types:span",
+        "//aos:macros",
     ],
 )
 
diff --git a/aos/flatbuffers.h b/aos/flatbuffers.h
index e556c0f..15740a1 100644
--- a/aos/flatbuffers.h
+++ b/aos/flatbuffers.h
@@ -5,6 +5,7 @@
 #include <string_view>
 
 #include "absl/types/span.h"
+#include "aos/macros.h"
 #include "flatbuffers/flatbuffers.h"
 #include "glog/logging.h"
 
@@ -30,12 +31,14 @@
   void Reset() { is_allocated_ = false; }
   bool is_allocated() const { return is_allocated_; }
 
+  bool allocated() { return is_allocated_; }
+
  private:
   bool is_allocated_ = false;
 };
 
 // This class is a fixed memory allocator which holds the data for a flatbuffer
-// in an array.
+// in a vector.
 class FixedAllocator : public FixedAllocatorBase {
  public:
   FixedAllocator(size_t size) : buffer_(size, 0) {}
@@ -55,7 +58,7 @@
 class PreallocatedAllocator : public FixedAllocatorBase {
  public:
   PreallocatedAllocator(void *data, size_t size) : data_(data), size_(size) {}
-  PreallocatedAllocator(const PreallocatedAllocator&) = delete;
+  PreallocatedAllocator(const PreallocatedAllocator &) = delete;
   PreallocatedAllocator(PreallocatedAllocator &&other)
       : data_(other.data_), size_(other.size_) {
     CHECK(!is_allocated());
@@ -229,6 +232,50 @@
   flatbuffers::DetachedBuffer buffer_;
 };
 
+// Array backed flatbuffer which manages building of the flatbuffer.
+template <typename T, size_t Size>
+class FlatbufferFixedAllocatorArray final : public Flatbuffer<T> {
+ public:
+  FlatbufferFixedAllocatorArray() : buffer_(), allocator_(&buffer_[0], Size) {
+    builder_ = flatbuffers::FlatBufferBuilder(Size, &allocator_);
+  }
+
+  flatbuffers::FlatBufferBuilder *Builder() {
+    if (allocator_.allocated()) {
+      LOG(FATAL) << "Array backed flatbuffer can only be built once";
+    }
+    return &builder_;
+  }
+
+  void Finish(flatbuffers::Offset<T> root) {
+    if (!allocator_.allocated()) {
+      LOG(FATAL) << "Cannot finish if never building";
+    }
+    builder_.Finish(root);
+    data_ = builder_.GetBufferPointer();
+    size_ = builder_.GetSize();
+  }
+
+  const uint8_t *data() const override {
+    CHECK_NOTNULL(data_);
+    return data_;
+  }
+  uint8_t *data() override {
+    CHECK_NOTNULL(data_);
+    return data_;
+  }
+  size_t size() const override { return size_; }
+
+ private:
+  std::array<uint8_t, Size> buffer_;
+  PreallocatedAllocator allocator_;
+  flatbuffers::FlatBufferBuilder builder_;
+  uint8_t *data_ = nullptr;
+  size_t size_ = 0;
+
+  DISALLOW_COPY_AND_ASSIGN(FlatbufferFixedAllocatorArray);
+};
+
 // This object associates the message type with the memory storing the
 // flatbuffer.  This only stores root tables.
 //
diff --git a/y2020/vision/v4l2_reader.cc b/y2020/vision/v4l2_reader.cc
index 727f8ba..f43a2ac 100644
--- a/y2020/vision/v4l2_reader.cc
+++ b/y2020/vision/v4l2_reader.cc
@@ -15,10 +15,7 @@
   PCHECK(fd_.get() != -1);
 
   // First, clean up after anybody else who left the device streaming.
-  {
-    int type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
-    PCHECK(Ioctl(VIDIOC_STREAMOFF, &type) == 0);
-  }
+  StreamOff();
 
   {
     struct v4l2_format format;
@@ -130,5 +127,19 @@
   PCHECK(Ioctl(VIDIOC_QBUF, &buffer) == 0);
 }
 
+void V4L2Reader::StreamOff() {
+  int type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+  const int result = Ioctl(VIDIOC_STREAMOFF, &type);
+  if (result == 0) {
+    return;
+  }
+  // Some devices (like Alex's webcam) return this if streaming isn't currently
+  // on, unlike what the documentations says should happen.
+  if (errno == EBUSY) {
+    return;
+  }
+  PLOG(FATAL) << "VIDIOC_STREAMOFF failed";
+}
+
 }  // namespace vision
 }  // namespace frc971
diff --git a/y2020/vision/v4l2_reader.h b/y2020/vision/v4l2_reader.h
index 969f4a8..bdf4a8e 100644
--- a/y2020/vision/v4l2_reader.h
+++ b/y2020/vision/v4l2_reader.h
@@ -88,6 +88,8 @@
 
   int Ioctl(unsigned long number, void *arg);
 
+  void StreamOff();
+
   // The mmaped V4L2 buffers.
   std::array<Buffer, kNumberBuffers> buffers_;