Increase VIDIOC_REQBUFS count from 2 to 4

media/video/capture/linux/video_capture_device_linux.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/video/capture/linux/video_capture_device_linux.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <poll.h>
 #if defined(OS_OPENBSD)
@@ skipping 10 matching lines @@
 #include "base/bind.h"
 #include "base/files/file_enumerator.h"
 #include "base/files/scoped_file.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/strings/stringprintf.h"
 
 namespace media {
 
 #define GET_V4L2_FOURCC_CHAR(a, index) ((char)( ((a) >> (8 * index)) & 0xff))
 
-// Max number of video buffers VideoCaptureDeviceLinux can allocate.
-const uint32 kMaxVideoBuffers = 2;
+// Desired number of video buffers to allocate. The actual number of allocated
+// buffers by v4l2 driver can be higher or lower than this number.
+// kNumVideoBuffers should not be too small, or Chrome may not return enough
+// buffers back to driver in time.
+const uint32 kNumVideoBuffers = 4;
 // Timeout in milliseconds v4l2_thread_ blocks waiting for a frame from the hw.
 enum { kCaptureTimeoutMs = 200 };
 // The number of continuous timeouts tolerated before treated as error.
 enum { kContinuousTimeoutLimit = 10 };
 // MJPEG is preferred if the width or height is larger than this.
 enum { kMjpegWidth = 640 };
 enum { kMjpegHeight = 480 };
 // Typical framerate, in fps
 enum { kTypicalFramerate = 30 };
 
@@ skipping 413 matching lines @@
   v4l2_task_runner_->PostTask(
       FROM_HERE,
       base::Bind(&VideoCaptureDeviceLinux::V4L2CaptureDelegate::DoCapture,
                  this));
 }
 
 bool VideoCaptureDeviceLinux::V4L2CaptureDelegate::AllocateVideoBuffers() {
   v4l2_requestbuffers r_buffer = {};
   r_buffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
   r_buffer.memory = V4L2_MEMORY_MMAP;
-  r_buffer.count = kMaxVideoBuffers;
+  r_buffer.count = kNumVideoBuffers;
   if (HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_REQBUFS, &r_buffer)) < 0) {
     DLOG(ERROR) << "Error requesting MMAP buffers from V4L2";
     return false;
   }
-  DCHECK_EQ(r_buffer.count, kMaxVideoBuffers);
-  r_buffer.count = std::min(r_buffer.count, kMaxVideoBuffers);
   buffer_pool_size_ = r_buffer.count;
   buffer_pool_ = new Buffer[buffer_pool_size_];
   for (unsigned int i = 0; i < r_buffer.count; ++i) {
     v4l2_buffer buffer = {};
     buffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
     buffer.memory = V4L2_MEMORY_MMAP;
     buffer.index = i;
     buffer.length = 1;
     if (HANDLE_EINTR(ioctl(device_fd_.get(), VIDIOC_QUERYBUF, &buffer)) < 0) {
       DLOG(ERROR) << "Error querying status of a MMAP V4L2 buffer";
@@ skipping 41 matching lines @@
 }
 
 void VideoCaptureDeviceLinux::V4L2CaptureDelegate::SetErrorState(
     const std::string& reason) {
   DCHECK(v4l2_task_runner_->BelongsToCurrentThread());
   is_capturing_ = false;
   client_->OnError(reason);
 }
 
 }  // namespace media