Mpeg2TS - estimate duration for video frames.

media/formats/mp2t/es_adapter_video.cc

+// Copyright 2014 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/formats/mp2t/es_adapter_video.h"
+
+#include "media/base/buffers.h"
+#include "media/base/stream_parser_buffer.h"
+#include "media/base/video_decoder_config.h"
+#include "media/formats/mp2t/mp2t_common.h"
+
+namespace media {
+namespace mp2t {
+
+// Arbitrary decision about the frame duration when there is no previous
+// hint about what could be the frame duration.
+static base::TimeDelta kDefaultFrameDuration(
+    base::TimeDelta::FromMilliseconds(40));
+
+// To calculate the frame duration, we make an assumption
+// that the timestamp of the next frame in presentation order
+// is no further than 5 frames away in decode order.
+// TODO(damienv): the previous assumption should cover most of the practical
+// cases. However, the right way to calculate the frame duration would be
+// to emulate the H264 dpb bumping process.
+static const size_t kHistorySize = 5;
+
+EsAdapterVideo::EsAdapterVideo(
+    const NewVideoConfigCB& new_video_config_cb,
+    const EmitBufferCB& emit_buffer_cb)
+  : new_video_config_cb_(new_video_config_cb),
+    emit_buffer_cb_(emit_buffer_cb),
+    has_valid_config_(false),
+    has_valid_frame_(false),
+    last_frame_duration_(kDefaultFrameDuration),
+    buffer_index_(0) {
+}
+
+EsAdapterVideo::~EsAdapterVideo() {
+}
+
+void EsAdapterVideo::Flush() {
+  ProcessPendingBuffers(true);
+}
+
+void EsAdapterVideo::OnConfigChanged(
+    const VideoDecoderConfig& video_decoder_config) {
+  config_list_.push_back(
+      ConfigEntry(buffer_index_ + buffer_list_.size(), video_decoder_config));
+  has_valid_config_ = true;
+  ProcessPendingBuffers(false);
+}
+
+void EsAdapterVideo::OnNewBuffer(
+    const scoped_refptr<StreamParserBuffer>& stream_parser_buffer) {
+  // Discard the incoming frame:
+  // - if it is not associated with any config,
+  // - or if only non-key frames have been added to a new segment.
+  if (!has_valid_config_ ||
+      (!has_valid_frame_ && !stream_parser_buffer->IsKeyframe())) {
+    if (discarded_frames_dts_.empty() ||
+        discarded_frames_min_pts_ > stream_parser_buffer->timestamp()) {
+      discarded_frames_min_pts_ = stream_parser_buffer->timestamp();
+    }
+    discarded_frames_dts_.push_back(
+        stream_parser_buffer->GetDecodeTimestamp());
+    return;
+  }
+
+  has_valid_frame_ = true;
+
+  if (!discarded_frames_dts_.empty())
+    ReplaceDiscardedFrames(stream_parser_buffer);
+
+  buffer_list_.push_back(stream_parser_buffer);
+  ProcessPendingBuffers(false);
+}
+
+void EsAdapterVideo::ProcessPendingBuffers(bool flush) {
+  DCHECK(has_valid_config_);
+
+  while (!buffer_list_.empty() &&
+         (flush || buffer_list_.size() > kHistorySize)) {
+    // Signal a config change, just before emitting the corresponding frame.
+    if (!config_list_.empty() && config_list_.front().first == buffer_index_) {
+      new_video_config_cb_.Run(config_list_.front().second);
+      config_list_.pop_front();
+    }
+
+    scoped_refptr<StreamParserBuffer> buffer = buffer_list_.front();
+    buffer_list_.pop_front();
+    buffer_index_++;
+
+    if (buffer->duration() == kNoTimestamp()) {
+      base::TimeDelta next_frame_pts = GetNextFramePts(buffer->timestamp());
+      if (next_frame_pts == kNoTimestamp()) {
+        // This can happen when emitting the very last buffer
+        // or if the stream do not meet the assumption behind |kHistorySize|.
+        buffer->set_duration(last_frame_duration_);
+      } else {
+        buffer->set_duration(next_frame_pts - buffer->timestamp());
+      }
+    }
+
+    emitted_pts_.push_back(buffer->timestamp());
+    if (emitted_pts_.size() > kHistorySize)
+      emitted_pts_.pop_front();
+
+    last_frame_duration_ = buffer->duration();
+    emit_buffer_cb_.Run(buffer);
+  }
+}
+
+base::TimeDelta EsAdapterVideo::GetNextFramePts(base::TimeDelta current_pts) {
+  base::TimeDelta next_pts = kNoTimestamp();
+
+  // Consider the timestamps of future frames (in decode order).
+  for (BufferQueue::const_iterator it = buffer_list_.begin();

[acolwell GONE FROM CHROMIUM, 2014/07/09 20:01:10]

nit: Might want to call out B-frames here since people might think the next
frame should be sufficient and won't think about the IPB case.

[damienv1, 2014/07/10 16:00:53]

Done.

+       it != buffer_list_.end(); ++it) {
+    if ((*it)->timestamp() < current_pts)
+      continue;
+    if (next_pts == kNoTimestamp() || next_pts > (*it)->timestamp())
+      next_pts = (*it)->timestamp();
+  }
+
+  // Consider the timestamps of previous frames (in decode order).
+  for (std::list<base::TimeDelta>::const_iterator it = emitted_pts_.begin();

[acolwell GONE FROM CHROMIUM, 2014/07/09 20:01:10]

This is for the duration of the last B frame in IPBBB right? Perhaps add why  we
need to consider previous frames to the comment?

[damienv1, 2014/07/10 16:00:53]

Done.

+       it != emitted_pts_.end(); ++it) {
+    if (*it < current_pts)
+      continue;
+    if (next_pts == kNoTimestamp() || next_pts > *it)
+      next_pts = *it;
+  }
+
+  return next_pts;
+}
+
+void EsAdapterVideo::ReplaceDiscardedFrames(
+    const scoped_refptr<StreamParserBuffer>& stream_parser_buffer) {
+  DCHECK(!discarded_frames_dts_.empty());
+  DCHECK(stream_parser_buffer->IsKeyframe());
+
+  // PTS is interpolated between the min PTS of discarded frames
+  // and the PTS of the first valid buffer.
+  base::TimeDelta pts = discarded_frames_min_pts_;
+  base::TimeDelta pts_delta =
+      (stream_parser_buffer->timestamp() - pts) / discarded_frames_dts_.size();
+
+  while (!discarded_frames_dts_.empty()) {
+    scoped_refptr<StreamParserBuffer> frame =
+        StreamParserBuffer::CopyFrom(
+            stream_parser_buffer->data(),
+            stream_parser_buffer->data_size(),
+            stream_parser_buffer->IsKeyframe(),
+            stream_parser_buffer->type(),
+            stream_parser_buffer->track_id());
+    frame->SetDecodeTimestamp(discarded_frames_dts_.front());
+    frame->set_timestamp(pts);
+    frame->set_duration(pts_delta);
+    buffer_list_.push_back(frame);
+    pts += pts_delta;
+    discarded_frames_dts_.pop_front();
+  }
+}
+
+}  // namespace mp2t
+}  // namespace media
+