media/capture/capture_resolution_chooser.cc

   1 // Copyright 2015 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "media/capture/capture_resolution_chooser.h"
   6
   7 #include <algorithm>
   8 #include <limits>
   9
  10 #include "base/strings/string_util.h"
  11 #include "media/base/limits.h"
  12 #include "media/base/video_util.h"
  13
  14 namespace media {
  15
  16 namespace {
  17
  18 // Each snapped frame size is an integer multiple of this many lines apart.
  19 // This is ideal for 16:9 content, but seems to also work well for many
  20 // arbitrary aspect ratios.
  21 const int kSnappedHeightStep = 90;
  22
  23 // The minimum amount of decrease in area between consecutive snapped frame
  24 // sizes.  This matters externally, where the end-to-end system is hunting for a
  25 // capture size that works within all resource bottlenecks.  If the snapped
  26 // frame sizes are too-close together, the end-to-end system cannot stablize.
  27 // If they are too-far apart, quality is being sacrificed.
  28 const int kMinAreaDecreasePercent = 15;
  29
  30 // Compute the minimum frame size from the given |max_frame_size| and
  31 // |resolution_change_policy|.
  32 gfx::Size ComputeMinimumCaptureSize(
  33     const gfx::Size& max_frame_size,
  34     ResolutionChangePolicy resolution_change_policy) {
  35   switch (resolution_change_policy) {
  36     case RESOLUTION_POLICY_FIXED_RESOLUTION:
  37       return max_frame_size;
  38     case RESOLUTION_POLICY_FIXED_ASPECT_RATIO: {
  39       // TODO(miu): This is a place-holder until "min constraints" are plumbed-
  40       // in from the MediaStream framework.  http://crbug.com/473336
  41       const int kMinLines = 180;
  42       if (max_frame_size.height() <= kMinLines)
  43         return max_frame_size;
  44       const gfx::Size result(
  45           kMinLines * max_frame_size.width() / max_frame_size.height(),
  46           kMinLines);
  47       if (result.width() <= 0 || result.width() > limits::kMaxDimension)
  48         return max_frame_size;
  49       return result;
  50     }
  51     case RESOLUTION_POLICY_ANY_WITHIN_LIMIT:
  52       return gfx::Size(1, 1);
  53   }
  54   NOTREACHED();
  55   return gfx::Size(1, 1);
  56 }
  57
  58 // Returns |size|, unless it exceeds |max_size| or is under |min_size|.  When
  59 // the bounds are exceeded, computes and returns an alternate size of similar
  60 // aspect ratio that is within the bounds.
  61 gfx::Size ComputeBoundedCaptureSize(const gfx::Size& size,
  62                                     const gfx::Size& min_size,
  63                                     const gfx::Size& max_size) {
  64   if (size.width() > max_size.width() || size.height() > max_size.height()) {
  65     gfx::Size result = ScaleSizeToFitWithinTarget(size, max_size);
  66     result.SetToMax(min_size);
  67     return result;
  68   } else if (size.width() < min_size.width() ||
  69              size.height() < min_size.height()) {
  70     gfx::Size result = ScaleSizeToEncompassTarget(size, min_size);
  71     result.SetToMin(max_size);
  72     return result;
  73   } else {
  74     return size;
  75   }
  76 }
  77
  78 // Returns true if the area of |a| is less than that of |b|.
  79 bool CompareByArea(const gfx::Size& a, const gfx::Size& b) {
  80   return a.GetArea() < b.GetArea();
  81 }
  82
  83 }  // namespace
  84
  85 CaptureResolutionChooser::CaptureResolutionChooser(
  86     const gfx::Size& max_frame_size,
  87     ResolutionChangePolicy resolution_change_policy)
  88     : max_frame_size_(max_frame_size),
  89       min_frame_size_(ComputeMinimumCaptureSize(max_frame_size,
  90                                                 resolution_change_policy)),
  91       resolution_change_policy_(resolution_change_policy),
  92       target_area_(std::numeric_limits<decltype(target_area_)>::max()) {
  93   DCHECK_LT(0, max_frame_size_.width());
  94   DCHECK_LT(0, max_frame_size_.height());
  95   DCHECK_LE(min_frame_size_.width(), max_frame_size_.width());
  96   DCHECK_LE(min_frame_size_.height(), max_frame_size_.height());
  97   DCHECK_LE(resolution_change_policy_, RESOLUTION_POLICY_LAST);
  98
  99   UpdateSnappedFrameSizes(max_frame_size_);
 100   RecomputeCaptureSize();
 101 }
 102
 103 CaptureResolutionChooser::~CaptureResolutionChooser() {}
 104
 105 void CaptureResolutionChooser::SetSourceSize(const gfx::Size& source_size) {
 106   if (source_size.IsEmpty())
 107     return;
 108
 109   switch (resolution_change_policy_) {
 110     case RESOLUTION_POLICY_FIXED_RESOLUTION:
 111       // Source size changes do not affect the frame resolution.  Frame
 112       // resolution is always fixed to |max_frame_size_|.
 113       break;
 114
 115     case RESOLUTION_POLICY_FIXED_ASPECT_RATIO:
 116       UpdateSnappedFrameSizes(ComputeBoundedCaptureSize(
 117           PadToMatchAspectRatio(source_size, max_frame_size_),
 118           min_frame_size_,
 119           max_frame_size_));
 120       RecomputeCaptureSize();
 121       break;
 122
 123     case RESOLUTION_POLICY_ANY_WITHIN_LIMIT:
 124       UpdateSnappedFrameSizes(ComputeBoundedCaptureSize(
 125           source_size, min_frame_size_, max_frame_size_));
 126       RecomputeCaptureSize();
 127       break;
 128   }
 129 }
 130
 131 void CaptureResolutionChooser::SetTargetFrameArea(int area) {
 132   DCHECK_GE(area, 0);
 133   target_area_ = area;
 134   RecomputeCaptureSize();
 135 }
 136
 137 gfx::Size CaptureResolutionChooser::FindNearestFrameSize(int area) const {
 138   const auto begin = snapped_sizes_.begin();
 139   const auto end = snapped_sizes_.end();
 140   DCHECK(begin != end);
 141   const gfx::Size area_as_size(area, 1);  // A facade for CompareByArea().
 142   const auto p = std::lower_bound(begin, end, area_as_size, &CompareByArea);
 143   if (p == end) {
 144     // Boundary case: The target |area| is greater than or equal to the
 145     // largest, so the largest size is closest.
 146     return *(end - 1);
 147   } else if (p == begin) {
 148     // Boundary case: The target |area| is smaller than the smallest, so the
 149     // smallest size is closest.
 150     return *begin;
 151   } else {
 152     // |p| points to the smallest size whose area is greater than or equal to
 153     // the target |area|.  The next smaller size could be closer to the target
 154     // |area|, so it must also be considered.
 155     const auto q = p - 1;
 156     return ((p->GetArea() - area) < (area - q->GetArea())) ? *p : *q;
 157   }
 158 }
 159
 160 gfx::Size CaptureResolutionChooser::FindLargerFrameSize(
 161     int area, int num_steps_up) const {
 162   DCHECK_GT(num_steps_up, 0);
 163   const auto begin = snapped_sizes_.begin();
 164   const auto end = snapped_sizes_.end();
 165   DCHECK(begin != end);
 166   const gfx::Size area_as_size(area, 1);  // A facade for CompareByArea().
 167   auto p = std::upper_bound(begin, end, area_as_size, &CompareByArea);
 168   // |p| is already pointing one step up.
 169   const int additional_steps_up = num_steps_up - 1;
 170   if ((end - p) > additional_steps_up)
 171     return *(p + additional_steps_up);
 172   else
 173     return *(end - 1);
 174 }
 175
 176 gfx::Size CaptureResolutionChooser::FindSmallerFrameSize(
 177     int area, int num_steps_down) const {
 178   DCHECK_GT(num_steps_down, 0);
 179   const auto begin = snapped_sizes_.begin();
 180   const auto end = snapped_sizes_.end();
 181   DCHECK(begin != end);
 182   const gfx::Size area_as_size(area, 1);  // A facade for CompareByArea().
 183   const auto p = std::lower_bound(begin, end, area_as_size, &CompareByArea);
 184   if ((p - begin) >= num_steps_down)
 185     return *(p - num_steps_down);
 186   else
 187     return *begin;
 188 }
 189
 190 void CaptureResolutionChooser::RecomputeCaptureSize() {
 191   const gfx::Size old_capture_size = capture_size_;
 192   capture_size_ = FindNearestFrameSize(target_area_);
 193   VLOG_IF(1, capture_size_ != old_capture_size)
 194       << "Recomputed capture size from " << old_capture_size.ToString()
 195       << " to " << capture_size_.ToString() << " ("
 196       << (100.0 * capture_size_.height() / snapped_sizes_.back().height())
 197       << "% of ideal size)";
 198 }
 199
 200 void CaptureResolutionChooser::UpdateSnappedFrameSizes(
 201     const gfx::Size& constrained_size) {
 202   // The |constrained_size| is always in the set of possible capture sizes and
 203   // is the largest one.
 204   snapped_sizes_.clear();
 205   snapped_sizes_.push_back(constrained_size);
 206
 207   // Repeatedly decrease the size in steps, adding each to |snapped_sizes_|.
 208   // However, skip the sizes that do not decrease in area by enough, relative to
 209   // the prior size.
 210   int last_area = constrained_size.GetArea();
 211   for (int height = constrained_size.height() - kSnappedHeightStep;
 212        height >= min_frame_size_.height();
 213        height -= kSnappedHeightStep) {
 214     const int width =
 215         height * constrained_size.width() / constrained_size.height();
 216     if (width < min_frame_size_.width())
 217       break;
 218     const int smaller_area = width * height;
 219     const int percent_decrease = 100 * (last_area - smaller_area) / last_area;
 220     if (percent_decrease >= kMinAreaDecreasePercent) {
 221       snapped_sizes_.push_back(gfx::Size(width, height));
 222       last_area = smaller_area;
 223     }
 224   }
 225
 226   // Reverse ordering, so that sizes are from smallest to largest.
 227   std::reverse(snapped_sizes_.begin(), snapped_sizes_.end());
 228
 229   if (VLOG_IS_ON(1)) {
 230     std::vector<std::string> stringified_sizes;
 231     for (const gfx::Size& size : snapped_sizes_)
 232       stringified_sizes.push_back(size.ToString());
 233     VLOG_STREAM(1) << "Recomputed snapped frame sizes: "
 234                    << base::JoinString(stringified_sizes, " <--> ");
 235   }
 236 }
 237
 238 }  // namespace media