Fix crash caused by removing the gap at the beginning of a media segment.

media/filters/source_buffer_stream.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/filters/source_buffer_stream.h"
 
 #include <algorithm>
 #include <map>
 
 #include "base/bind.h"
@@ skipping 150 matching lines @@
   // Returns the timestamp of the last buffer in the range.
   base::TimeDelta GetEndTimestamp() const;
 
   // Returns the timestamp for the end of the buffered region in this range.
   // This is an approximation if the duration for the last buffer in the range
   // is unset.
   base::TimeDelta GetBufferedEndTimestamp() const;
 
   // Gets the timestamp for the keyframe that is after |timestamp|. If
   // there isn't a keyframe in the range after |timestamp| then kNoTimestamp()
-  // is returned.
+  // is returned. If |timestamp| is in the "gap" between the value

[wolenetz, 2014/06/12 19:20:49]

nit: these new pieces seem wrapped at less than 80 chars max. If vim'ing, select
comment lines and use 'gq' command sequence to re-wrap.

[acolwell GONE FROM CHROMIUM, 2014/06/12 20:17:59]

Done.

+  // returned by GetStartTimestamp() and the timestamp on the first
+  // buffer in |buffers_|, then |timestamp| is returned.
   base::TimeDelta NextKeyframeTimestamp(base::TimeDelta timestamp);
 
   // Gets the timestamp for the closest keyframe that is <= |timestamp|. If
   // there isn't a keyframe before |timestamp| or |timestamp| is outside
   // this range, then kNoTimestamp() is returned.
   base::TimeDelta KeyframeBeforeTimestamp(base::TimeDelta timestamp);
 
   // Returns whether a buffer with a starting timestamp of |timestamp| would
   // belong in this range. This includes a buffer that would be appended to
   // the end of the range.
@@ skipping 1518 matching lines @@
 SourceBufferRange::SourceBufferRange(
     SourceBufferStream::Type type, const BufferQueue& new_buffers,
     base::TimeDelta media_segment_start_time,
     const InterbufferDistanceCB& interbuffer_distance_cb)
     : type_(type),
       keyframe_map_index_base_(0),
       next_buffer_index_(-1),
       media_segment_start_time_(media_segment_start_time),
       interbuffer_distance_cb_(interbuffer_distance_cb),
       size_in_bytes_(0) {
   DCHECK(!new_buffers.empty());

[wolenetz, 2014/06/12 19:20:49]

nit: to better protect against undefined behavior on possible re-introduction
later of a path creating empty ranges that are subsequently operated on blindly
assuming non-emptiness, change this to a CHECK?

[acolwell GONE FROM CHROMIUM, 2014/06/12 20:17:59]

Done.

   DCHECK(new_buffers.front()->IsKeyframe());
   DCHECK(!interbuffer_distance_cb.is_null());
   AppendBuffersToEnd(new_buffers);
 }
 
 void SourceBufferRange::AppendBuffersToEnd(const BufferQueue& new_buffers) {
   DCHECK(buffers_.empty() || CanAppendBuffersToEnd(new_buffers));
   DCHECK(media_segment_start_time_ == kNoTimestamp() ||
          media_segment_start_time_ <=
              new_buffers.front()->GetDecodeTimestamp());
@@ skipping 46 matching lines @@
   DCHECK_LT(next_buffer_index_, static_cast<int>(buffers_.size()));
 }
 
 void SourceBufferRange::SeekToStart() {
   DCHECK(!buffers_.empty());
   next_buffer_index_ = 0;
 }
 
 SourceBufferRange* SourceBufferRange::SplitRange(
     base::TimeDelta timestamp, bool is_exclusive) {
+  CHECK(!buffers_.empty());
+
   // Find the first keyframe after |timestamp|. If |is_exclusive|, do not
   // include keyframes at |timestamp|.
   KeyframeMap::iterator new_beginning_keyframe =
       GetFirstKeyframeAt(timestamp, is_exclusive);
 
   // If there is no keyframe after |timestamp|, we can't split the range.
   if (new_beginning_keyframe == keyframe_map_.end())
     return NULL;
 
   // Remove the data beginning at |keyframe_index| from |buffers_| and save it
   // 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());
+
+  base::TimeDelta new_range_start_timestamp = kNoTimestamp();
+  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.
+    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(
-          type_, removed_buffers, kNoTimestamp(), interbuffer_distance_cb_);
+          type_, removed_buffers, new_range_start_timestamp,
+          interbuffer_distance_cb_);
 
   // If the next buffer position is now in |split_range|, update the state of
   // this range and |split_range| accordingly.
   if (next_buffer_index_ >= static_cast<int>(buffers_.size())) {
     split_range->next_buffer_index_ = next_buffer_index_ - keyframe_index;
     ResetNextBufferPosition();
   }
 
   return split_range;
 }
@@ skipping 198 matching lines @@
   }
   buffers_.erase(starting_point, ending_point);
 }
 
 bool SourceBufferRange::TruncateAt(
     const BufferQueue::iterator& starting_point, BufferQueue* removed_buffers) {
   DCHECK(!removed_buffers || removed_buffers->empty());
 
   // Return if we're not deleting anything.
   if (starting_point == buffers_.end())
-    return false;
+    return buffers_.empty();
 
   // Reset the next buffer index if we will be deleting the buffer that's next
   // in sequence.
   if (HasNextBufferPosition()) {
     base::TimeDelta next_buffer_timestamp = GetNextTimestamp();
     if (next_buffer_timestamp == kNoTimestamp() ||
         next_buffer_timestamp >= (*starting_point)->GetDecodeTimestamp()) {
       if (HasNextBuffer() && removed_buffers) {
         int starting_offset = starting_point - buffers_.begin();
         int next_buffer_offset = next_buffer_index_ - starting_offset;
@@ skipping 128 matching lines @@
 base::TimeDelta SourceBufferRange::NextKeyframeTimestamp(
     base::TimeDelta timestamp) {
   DCHECK(!keyframe_map_.empty());
 
   if (timestamp < GetStartTimestamp() || timestamp >= GetBufferedEndTimestamp())
     return kNoTimestamp();
 
   KeyframeMap::iterator itr = GetFirstKeyframeAt(timestamp, false);
   if (itr == keyframe_map_.end())
     return kNoTimestamp();
+
+  // 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_ &&
+      timestamp < itr->first) {
+    return timestamp;
+  }
+
   return itr->first;
 }
 
 base::TimeDelta SourceBufferRange::KeyframeBeforeTimestamp(
     base::TimeDelta timestamp) {
   DCHECK(!keyframe_map_.empty());
 
   if (timestamp < GetStartTimestamp() || timestamp >= GetBufferedEndTimestamp())
     return kNoTimestamp();
 
@@ skipping 63 matching lines @@
     return false;
 
   DCHECK_NE(have_splice_buffers, have_preroll_buffer);
   splice_buffers_index_ = 0;
   pending_buffer_.swap(*out_buffer);
   pending_buffers_complete_ = false;
   return true;
 }
 
 }  // namespace media