Don't rebase timestamps for positive start times.

media/filters/ffmpeg_demuxer.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/ffmpeg_demuxer.h"
 
 #include <algorithm>
 #include <string>
 
 #include "base/base64.h"
@@ skipping 287 matching lines @@
     const bool is_audio = type() == AUDIO;
 
     // If this is an OGG file with negative timestamps don't rebase any other
     // stream types against the negative starting time.
     base::TimeDelta start_time = demuxer_->start_time();
     if (fixup_negative_ogg_timestamps_ && !is_audio &&
         start_time < base::TimeDelta()) {
       start_time = base::TimeDelta();
     }
 
+    // Don't rebase timestamps for positive start times, the HTML Media Spec
+    // details this in section "4.8.10.6 Offsets into the media resource." We
+    // will still need to rebase timestamps before seeking with FFmpeg though.
+    if (start_time > base::TimeDelta())
+      start_time = base::TimeDelta();
+
     buffer->set_timestamp(stream_timestamp - start_time);
 
     // If enabled, mark audio packets with negative timestamps for post-decode
     // discard.
     if (fixup_negative_ogg_timestamps_ && is_audio &&
         stream_timestamp < base::TimeDelta() &&
         buffer->duration() != kNoTimestamp()) {
       if (stream_timestamp + buffer->duration() < base::TimeDelta()) {
         // Discard the entire packet if it's entirely before zero.
         buffer->set_discard_padding(
@@ skipping 263 matching lines @@
 
 void FFmpegDemuxer::Seek(base::TimeDelta time, const PipelineStatusCB& cb) {
   DCHECK(task_runner_->BelongsToCurrentThread());
   CHECK(!pending_seek_);
 
   // TODO(scherkus): Inspect |pending_read_| and cancel IO via |blocking_url_|,
   // otherwise we can end up waiting for a pre-seek read to complete even though
   // we know we're going to drop it on the floor.
 
   // FFmpeg requires seeks to be adjusted according to the lowest starting time.
-  const base::TimeDelta seek_time = time + start_time_;
+  // Since EnqueuePacket() rebased negative timestamps by the start time, we
+  // must correct the shift here.
+  //
+  // Additionally, to workaround limitations in how we expose seekable ranges to
+  // Blink (http://crbug.com/137275), we also want to clamp seeks before the
+  // start time to the start time.
+  const base::TimeDelta seek_time =
+      start_time_ < base::TimeDelta() ? time + start_time_
+                                      : time < start_time_ ? start_time_ : time;
 
   // Choose the seeking stream based on whether it contains the seek time, if no
   // match can be found prefer the preferred stream.
   //
   // TODO(dalecurtis): Currently FFmpeg does not ensure that all streams in a
   // given container will demux all packets after the seek point.  Instead it
   // only guarantees that all packets after the file position of the seek will
   // be demuxed.  It's an open question whether FFmpeg should fix this:
   // http://lists.ffmpeg.org/pipermail/ffmpeg-devel/2014-June/159212.html
   // Tracked by http://crbug.com/387996.
@@ skipping 628 matching lines @@
   }
   for (size_t i = 0; i < buffered.size(); ++i)
     host_->AddBufferedTimeRange(buffered.start(i), buffered.end(i));
 }
 
 void FFmpegDemuxer::OnDataSourceError() {
   host_->OnDemuxerError(PIPELINE_ERROR_READ);
 }
 
 }  // namespace media