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- // Copyright 2015 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/capture/content/capture_resolution_chooser.h"
- #include <algorithm>
- #include <limits>
- #include "base/logging.h"
- #include "base/strings/string_util.h"
- #include "media/base/video_util.h"
- namespace media {
- namespace {
- // Each snapped frame size is an integer multiple of this many lines apart.
- // This is ideal for 16:9 content, but seems to also work well for many
- // arbitrary aspect ratios.
- const int kSnappedHeightStep = 90;
- // The minimum amount of decrease in area between consecutive snapped frame
- // sizes. This matters externally, where the end-to-end system is hunting for a
- // capture size that works within all resource bottlenecks. If the snapped
- // frame sizes are too-close together, the end-to-end system cannot stablize.
- // If they are too-far apart, quality is being sacrificed.
- const int kMinAreaDecreasePercent = 15;
- // Returns |size|, unless it exceeds |max_size| or is under |min_size|. When
- // the bounds are exceeded, computes and returns an alternate size of similar
- // aspect ratio that is within the bounds.
- gfx::Size ComputeBoundedCaptureSize(const gfx::Size& size,
- const gfx::Size& min_size,
- const gfx::Size& max_size) {
- if (size.width() > max_size.width() || size.height() > max_size.height()) {
- gfx::Size result = ScaleSizeToFitWithinTarget(size, max_size);
- result.SetToMax(min_size);
- return result;
- } else if (size.width() < min_size.width() ||
- size.height() < min_size.height()) {
- gfx::Size result = ScaleSizeToEncompassTarget(size, min_size);
- result.SetToMin(max_size);
- return result;
- } else {
- return size;
- }
- }
- // Returns true if the area of |a| is less than that of |b|.
- bool CompareByArea(const gfx::Size& a, const gfx::Size& b) {
- return a.GetArea() < b.GetArea();
- }
- } // namespace
- // static
- constexpr gfx::Size CaptureResolutionChooser::kDefaultCaptureSize;
- CaptureResolutionChooser::CaptureResolutionChooser()
- : min_frame_size_(kDefaultCaptureSize),
- max_frame_size_(kDefaultCaptureSize),
- apply_aspect_ratio_adjustment_(false),
- target_area_(std::numeric_limits<decltype(target_area_)>::max()),
- capture_size_(kDefaultCaptureSize),
- snapped_sizes_({kDefaultCaptureSize}) {}
- CaptureResolutionChooser::~CaptureResolutionChooser() = default;
- void CaptureResolutionChooser::SetConstraints(const gfx::Size& min_frame_size,
- const gfx::Size& max_frame_size,
- bool use_fixed_aspect_ratio) {
- DCHECK_LT(0, min_frame_size.width());
- DCHECK_LT(0, min_frame_size.height());
- DCHECK_LE(min_frame_size.width(), max_frame_size.width());
- DCHECK_LE(min_frame_size.height(), max_frame_size.height());
- min_frame_size_ = min_frame_size;
- max_frame_size_ = max_frame_size;
- apply_aspect_ratio_adjustment_ =
- (min_frame_size != max_frame_size && use_fixed_aspect_ratio);
- UpdateSnappedFrameSizes();
- RecomputeCaptureSize();
- }
- void CaptureResolutionChooser::SetSourceSize(const gfx::Size& source_size) {
- source_size_ = source_size;
- UpdateSnappedFrameSizes();
- RecomputeCaptureSize();
- }
- void CaptureResolutionChooser::SetTargetFrameArea(int area) {
- DCHECK_GE(area, 0);
- target_area_ = area;
- RecomputeCaptureSize();
- }
- gfx::Size CaptureResolutionChooser::FindNearestFrameSize(int area) const {
- const auto begin = snapped_sizes_.begin();
- const auto end = snapped_sizes_.end();
- DCHECK(begin != end);
- const gfx::Size area_as_size(area, 1); // A facade for CompareByArea().
- const auto p = std::lower_bound(begin, end, area_as_size, &CompareByArea);
- if (p == end) {
- // Boundary case: The target |area| is greater than or equal to the
- // largest, so the largest size is closest.
- return *(end - 1);
- } else if (p == begin) {
- // Boundary case: The target |area| is smaller than the smallest, so the
- // smallest size is closest.
- return *begin;
- } else {
- // |p| points to the smallest size whose area is greater than or equal to
- // the target |area|. The next smaller size could be closer to the target
- // |area|, so it must also be considered.
- const auto q = p - 1;
- return ((p->GetArea() - area) < (area - q->GetArea())) ? *p : *q;
- }
- }
- gfx::Size CaptureResolutionChooser::FindLargerFrameSize(
- int area,
- int num_steps_up) const {
- DCHECK_GT(num_steps_up, 0);
- const auto begin = snapped_sizes_.begin();
- const auto end = snapped_sizes_.end();
- DCHECK(begin != end);
- const gfx::Size area_as_size(area, 1); // A facade for CompareByArea().
- auto p = std::upper_bound(begin, end, area_as_size, &CompareByArea);
- // |p| is already pointing one step up.
- const int additional_steps_up = num_steps_up - 1;
- if ((end - p) > additional_steps_up)
- return *(p + additional_steps_up);
- else
- return *(end - 1);
- }
- gfx::Size CaptureResolutionChooser::FindSmallerFrameSize(
- int area,
- int num_steps_down) const {
- DCHECK_GT(num_steps_down, 0);
- const auto begin = snapped_sizes_.begin();
- const auto end = snapped_sizes_.end();
- DCHECK(begin != end);
- const gfx::Size area_as_size(area, 1); // A facade for CompareByArea().
- const auto p = std::lower_bound(begin, end, area_as_size, &CompareByArea);
- if ((p - begin) >= num_steps_down)
- return *(p - num_steps_down);
- else
- return *begin;
- }
- void CaptureResolutionChooser::RecomputeCaptureSize() {
- const gfx::Size old_capture_size = capture_size_;
- capture_size_ = FindNearestFrameSize(target_area_);
- VLOG_IF(1, capture_size_ != old_capture_size)
- << "Recomputed capture size from " << old_capture_size.ToString()
- << " to " << capture_size_.ToString() << " ("
- << (100.0 * capture_size_.height() / snapped_sizes_.back().height())
- << "% of ideal size)";
- }
- void CaptureResolutionChooser::UpdateSnappedFrameSizes() {
- // Compute the largest snapped frame size, and the one that will determine the
- // aspect ratio of all the snapped frame sizes. If the |source_size_| has not
- // yet been set, use the |capture_size_| as a substitute.
- gfx::Size constrained_size =
- source_size_.IsEmpty() ? capture_size_ : source_size_;
- constrained_size = ComputeBoundedCaptureSize(
- apply_aspect_ratio_adjustment_
- ? PadToMatchAspectRatio(constrained_size, max_frame_size_)
- : constrained_size,
- min_frame_size_, max_frame_size_);
- // Start with the constrained size as the largest in the set.
- snapped_sizes_.clear();
- snapped_sizes_.push_back(constrained_size);
- // Repeatedly decrease the size in steps, adding each to |snapped_sizes_|.
- // However, skip the sizes that do not decrease in area by enough, relative to
- // the prior size.
- int last_area = constrained_size.GetArea();
- for (int height = constrained_size.height() - kSnappedHeightStep;
- height >= min_frame_size_.height(); height -= kSnappedHeightStep) {
- const int width =
- height * constrained_size.width() / constrained_size.height();
- if (width < min_frame_size_.width())
- break;
- const int smaller_area = width * height;
- const int percent_decrease = 100 * (last_area - smaller_area) / last_area;
- if (percent_decrease >= kMinAreaDecreasePercent) {
- snapped_sizes_.push_back(gfx::Size(width, height));
- last_area = smaller_area;
- }
- }
- // Reverse ordering, so that sizes are from smallest to largest.
- std::reverse(snapped_sizes_.begin(), snapped_sizes_.end());
- if (VLOG_IS_ON(1)) {
- std::vector<std::string> stringified_sizes;
- for (const gfx::Size& size : snapped_sizes_)
- stringified_sizes.push_back(size.ToString());
- VLOG_STREAM(1) << "Recomputed snapped frame sizes: "
- << base::JoinString(stringified_sizes, " <--> ");
- }
- }
- } // namespace media
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