Reland: MSE: Relax the 'media segment must begin with keyframe' requirement

media/filters/source_buffer_range.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/filters/source_buffer_range.h"
 
 #include <algorithm>
 
 #include "media/base/timestamp_constants.h"
 
 namespace media {
 
 // Comparison operators for std::upper_bound() and std::lower_bound().
 static bool CompareTimeDeltaToStreamParserBuffer(
     const DecodeTimestamp& decode_timestamp,
     const scoped_refptr<StreamParserBuffer>& buffer) {
   return decode_timestamp < buffer->GetDecodeTimestamp();
 }
 static bool CompareStreamParserBufferToTimeDelta(
     const scoped_refptr<StreamParserBuffer>& buffer,
     const DecodeTimestamp& decode_timestamp) {
   return buffer->GetDecodeTimestamp() < decode_timestamp;
 }
 
-bool SourceBufferRange::AllowSameTimestamp(
-    bool prev_is_keyframe, bool current_is_keyframe) {
-  return prev_is_keyframe || !current_is_keyframe;
+bool SourceBufferRange::IsUncommonSameTimestampSequence(
+    bool prev_is_keyframe,
+    bool current_is_keyframe) {
+  return current_is_keyframe && !prev_is_keyframe;
 }
 
 SourceBufferRange::SourceBufferRange(
-    GapPolicy gap_policy, const BufferQueue& new_buffers,
-    DecodeTimestamp media_segment_start_time,
+    GapPolicy gap_policy,
+    const BufferQueue& new_buffers,
+    DecodeTimestamp range_start_time,
     const InterbufferDistanceCB& interbuffer_distance_cb)
     : gap_policy_(gap_policy),
       keyframe_map_index_base_(0),
       next_buffer_index_(-1),
-      media_segment_start_time_(media_segment_start_time),
+      range_start_time_(range_start_time),
       interbuffer_distance_cb_(interbuffer_distance_cb),
       size_in_bytes_(0) {
   CHECK(!new_buffers.empty());
   DCHECK(new_buffers.front()->is_key_frame());
   DCHECK(!interbuffer_distance_cb.is_null());
-  AppendBuffersToEnd(new_buffers);
+  AppendBuffersToEnd(new_buffers, range_start_time_);
 }
 
 SourceBufferRange::~SourceBufferRange() {}
 
-void SourceBufferRange::AppendBuffersToEnd(const BufferQueue& new_buffers) {
-  DCHECK(buffers_.empty() || CanAppendBuffersToEnd(new_buffers));
-  DCHECK(media_segment_start_time_ == kNoDecodeTimestamp() ||
-         media_segment_start_time_ <=
-             new_buffers.front()->GetDecodeTimestamp());
+void SourceBufferRange::AppendBuffersToEnd(
+    const BufferQueue& new_buffers,
+    DecodeTimestamp new_buffers_group_start_timestamp) {
+  DCHECK(buffers_.empty() ||

[chcunningham, 2016/02/12 22:46:40]

DCHECK -> CHECK?

[wolenetz, 2016/02/24 00:34:46]

Done.

+         CanAppendBuffersToEnd(new_buffers, new_buffers_group_start_timestamp));
+  DCHECK(range_start_time_ == kNoDecodeTimestamp() ||

[chcunningham, 2016/02/12 22:46:40]

Can range start time really be kNoDecodeTimestamp? What scenario?

[wolenetz, 2016/02/24 00:34:46]

Yes. See the comment for |range_start_time_| in the header. See also
SplitRange()'s "new_range_start_timestamp", DeleteGOPFromFront(), etc. tl;dr:
it's kNoDecodeTimestamp when the front of a range is involved in a remove such
that it may no longer be associated with a "coded frame group start time". In
such case, GetStartTimestamp() just returns the DTS of the first buffer in the
range (which must not be empty....)

[chcunningham, 2016/02/24 19:06:26]

Acknowledged.

+         range_start_time_ <= new_buffers.front()->GetDecodeTimestamp());
 
   AdjustEstimatedDurationForNewAppend(new_buffers);
 
   for (BufferQueue::const_iterator itr = new_buffers.begin();
        itr != new_buffers.end();
        ++itr) {
     DCHECK((*itr)->GetDecodeTimestamp() != kNoDecodeTimestamp());
     buffers_.push_back(*itr);
     size_in_bytes_ += (*itr)->data_size();
 
@@ skipping 84 matching lines @@
   // into |removed_buffers|.
   int keyframe_index =
       new_beginning_keyframe->second - keyframe_map_index_base_;
   DCHECK_LT(keyframe_index, static_cast<int>(buffers_.size()));
   BufferQueue::iterator starting_point = buffers_.begin() + keyframe_index;
   BufferQueue removed_buffers(starting_point, buffers_.end());
 
   DecodeTimestamp new_range_start_timestamp = kNoDecodeTimestamp();
   if (GetStartTimestamp() < buffers_.front()->GetDecodeTimestamp() &&
       timestamp < removed_buffers.front()->GetDecodeTimestamp()) {
-    // The split is in the gap between |media_segment_start_time_| and
-    // the first buffer of the new range so we should set the start
-    // time of the new range to |timestamp| so we preserve part of the
-    // gap in the new range.
+    // The split is in the gap between |range_start_time_| and the first buffer
+    // of the new range so we should set the start time of the new range to
+    // |timestamp| so we preserve part of the gap in the new range.
     new_range_start_timestamp = timestamp;
   }
 
   keyframe_map_.erase(new_beginning_keyframe, keyframe_map_.end());
   FreeBufferRange(starting_point, buffers_.end());
 
   // Create a new range with |removed_buffers|.
   SourceBufferRange* split_range =
       new SourceBufferRange(
           gap_policy_, removed_buffers, new_range_start_timestamp,
@@ skipping 92 matching lines @@
 
   // Update |keyframe_map_index_base_| to account for the deleted buffers.
   keyframe_map_index_base_ += buffers_deleted;
 
   if (next_buffer_index_ > -1) {
     next_buffer_index_ -= buffers_deleted;
     CHECK_GE(next_buffer_index_, 0) << next_buffer_index_ << ", deleted "
                                     << buffers_deleted;
   }
 
-  // Invalidate media segment start time if we've deleted the first buffer of
-  // the range.
+  // Invalidate range start time if we've deleted the first buffer of the range.
   if (buffers_deleted > 0)
-    media_segment_start_time_ = kNoDecodeTimestamp();
+    range_start_time_ = kNoDecodeTimestamp();
 
   return total_bytes_deleted;
 }
 
 size_t SourceBufferRange::DeleteGOPFromBack(BufferQueue* deleted_buffers) {
   DCHECK(!LastGOPContainsNextBufferPosition());
   DCHECK(deleted_buffers);
 
   // Remove the last GOP's keyframe from the |keyframe_map_|.
   KeyframeMap::iterator back = keyframe_map_.end();
@@ skipping 187 matching lines @@
 }
 
 void SourceBufferRange::AppendRangeToEnd(const SourceBufferRange& range,
                                          bool transfer_current_position) {
   DCHECK(CanAppendRangeToEnd(range));
   DCHECK(!buffers_.empty());
 
   if (transfer_current_position && range.next_buffer_index_ >= 0)
     next_buffer_index_ = range.next_buffer_index_ + buffers_.size();
 
-  AppendBuffersToEnd(range.buffers_);
+  AppendBuffersToEnd(range.buffers_, kNoDecodeTimestamp());
 }
 
 bool SourceBufferRange::CanAppendRangeToEnd(
     const SourceBufferRange& range) const {
-  return CanAppendBuffersToEnd(range.buffers_);
+  return CanAppendBuffersToEnd(range.buffers_, kNoDecodeTimestamp());
 }
 
 bool SourceBufferRange::CanAppendBuffersToEnd(
-    const BufferQueue& buffers) const {
+    const BufferQueue& buffers,
+    DecodeTimestamp new_buffers_group_start_timestamp) const {
   DCHECK(!buffers_.empty());
-  return IsNextInSequence(buffers.front()->GetDecodeTimestamp(),
-                          buffers.front()->is_key_frame());
+  if (new_buffers_group_start_timestamp == kNoDecodeTimestamp()) {
+    return IsNextInSequence(buffers.front()->GetDecodeTimestamp());
+  }
+  DCHECK(new_buffers_group_start_timestamp >= GetEndTimestamp());
+  DCHECK(buffers.front()->GetDecodeTimestamp() >=
+         new_buffers_group_start_timestamp);
+  return IsNextInSequence(new_buffers_group_start_timestamp);
 }
 
 bool SourceBufferRange::BelongsToRange(DecodeTimestamp timestamp) const {
   DCHECK(!buffers_.empty());
 
-  return (IsNextInSequence(timestamp, false) ||
+  return (IsNextInSequence(timestamp) ||
           (GetStartTimestamp() <= timestamp && timestamp <= GetEndTimestamp()));
 }
 
 bool SourceBufferRange::CanSeekTo(DecodeTimestamp timestamp) const {
   DecodeTimestamp start_timestamp =
       std::max(DecodeTimestamp(), GetStartTimestamp() - GetFudgeRoom());
   return !keyframe_map_.empty() && start_timestamp <= timestamp &&
       timestamp < GetBufferedEndTimestamp();
 }
 
 bool SourceBufferRange::CompletelyOverlaps(
     const SourceBufferRange& range) const {
   return GetStartTimestamp() <= range.GetStartTimestamp() &&
       GetEndTimestamp() >= range.GetEndTimestamp();
 }
 
 bool SourceBufferRange::EndOverlaps(const SourceBufferRange& range) const {
   return range.GetStartTimestamp() <= GetEndTimestamp() &&
       GetEndTimestamp() < range.GetEndTimestamp();
 }
 
 DecodeTimestamp SourceBufferRange::GetStartTimestamp() const {
   DCHECK(!buffers_.empty());
-  DecodeTimestamp start_timestamp = media_segment_start_time_;
+  DecodeTimestamp start_timestamp = range_start_time_;
   if (start_timestamp == kNoDecodeTimestamp())
     start_timestamp = buffers_.front()->GetDecodeTimestamp();
   return start_timestamp;
 }
 
 DecodeTimestamp SourceBufferRange::GetEndTimestamp() const {
   DCHECK(!buffers_.empty());
   return buffers_.back()->GetDecodeTimestamp();
 }
 
 DecodeTimestamp SourceBufferRange::GetBufferedEndTimestamp() const {
   DCHECK(!buffers_.empty());
   base::TimeDelta duration = buffers_.back()->duration();
   if (duration == kNoTimestamp() || duration == base::TimeDelta())
     duration = GetApproximateDuration();
   return GetEndTimestamp() + duration;
 }
 
 DecodeTimestamp SourceBufferRange::NextKeyframeTimestamp(
     DecodeTimestamp timestamp) {
   DCHECK(!keyframe_map_.empty());
 
   if (timestamp < GetStartTimestamp() || timestamp >= GetBufferedEndTimestamp())
     return kNoDecodeTimestamp();
 
   KeyframeMap::iterator itr = GetFirstKeyframeAt(timestamp, false);
   if (itr == keyframe_map_.end())
     return kNoDecodeTimestamp();
 
-  // If the timestamp is inside the gap between the start of the media
-  // segment and the first buffer, then just pretend there is a
-  // keyframe at the specified timestamp.
-  if (itr == keyframe_map_.begin() &&
-      timestamp > media_segment_start_time_ &&
+  // If the timestamp is inside the gap between the start of the coded frame
+  // group and the first buffer, then just pretend there is a keyframe at the

[chcunningham, 2016/02/12 22:46:40]

Why do we pretend? Why not return the actual timestamp of the first key frame?

[wolenetz, 2016/02/24 00:34:46]

I think it simplifies seeking by SBS. (See FindNewSelectedRangeSeekTimestamp(),
for instance). It simplifies pruning of SBS |track_buffer_| in muxed
SourceBuffer in the presence of a jagged start (see near the end of
SBS::Append() for the pruning.) 
Perhaps we could "simplify" it better, but out of scope of this CL.

[chcunningham, 2016/02/24 19:06:26]

Ack. SBR and SBS seem annoyingly aware/reliant of/on each others internal
workings. Not your fault... just whining about it.

+  // specified timestamp.
+  if (itr == keyframe_map_.begin() && timestamp > range_start_time_ &&
       timestamp < itr->first) {
     return timestamp;
   }
 
   return itr->first;
 }
 
 DecodeTimestamp SourceBufferRange::KeyframeBeforeTimestamp(
     DecodeTimestamp timestamp) {
   DCHECK(!keyframe_map_.empty());
 
   if (timestamp < GetStartTimestamp() || timestamp >= GetBufferedEndTimestamp())
     return kNoDecodeTimestamp();
 
   return GetFirstKeyframeAtOrBefore(timestamp)->first;
 }
 
-bool SourceBufferRange::IsNextInSequence(
-    DecodeTimestamp timestamp, bool is_key_frame) const {
+bool SourceBufferRange::IsNextInSequence(DecodeTimestamp timestamp) const {
   DecodeTimestamp end = buffers_.back()->GetDecodeTimestamp();
-  if (end < timestamp &&
-      (gap_policy_ == ALLOW_GAPS ||
-       timestamp <= end + GetFudgeRoom())) {
-    return true;
-  }
-
-  return timestamp == end && AllowSameTimestamp(
-      buffers_.back()->is_key_frame(), is_key_frame);
+  return (end == timestamp ||
+          (end < timestamp &&
+           (gap_policy_ == ALLOW_GAPS || timestamp <= end + GetFudgeRoom())));
 }
 
 base::TimeDelta SourceBufferRange::GetFudgeRoom() const {
   // Because we do not know exactly when is the next timestamp, any buffer
   // that starts within 2x the approximate duration of a buffer is considered
   // within this range.
   return 2 * GetApproximateDuration();
 }
 
 base::TimeDelta SourceBufferRange::GetApproximateDuration() const {
@@ skipping 27 matching lines @@
     }
 
     if (buffer->timestamp() + buffer->duration() <= start.ToPresentationTime())
       continue;
     buffers->push_back(buffer);
   }
   return previous_size < buffers->size();
 }
 
 }  // namespace media