A video tag should play content src is set asynchronously with preload is disabled.

third_party/WebKit/Source/core/html/HTMLMediaElement.cpp

 /*
  * Copyright (C) 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights
  * reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 603 matching lines @@
     const AttributeModificationParams& params) {
   const QualifiedName& name = params.name;
   if (name == srcAttr) {
     BLINK_MEDIA_LOG << "parseAttribute(" << (void*)this
                     << ", srcAttr, old=" << params.old_value
                     << ", new=" << params.new_value << ")";
     // Trigger a reload, as long as the 'src' attribute is present.
     if (!params.new_value.IsNull()) {
       ignore_preload_none_ = false;
       InvokeLoadAlgorithm();
+      if (pending_play_) {
+        if (!paused_ && !playing_) {
+          PlayInternal();
+        } else {
+          pending_play_ = false;
+        }
+      }
     }
   } else if (name == controlsAttr) {
     UseCounter::Count(GetDocument(),
                       UseCounter::kHTMLMediaElementControlsAttribute);
     UpdateControlsVisibility();
   } else if (name == controlslistAttr) {
     UseCounter::Count(GetDocument(),
                       UseCounter::kHTMLMediaElementControlsListAttribute);
     if (params.old_value != params.new_value) {
       controls_list_->DidUpdateAttributeValue(params.old_value,
@@ skipping 1637 matching lines @@
   }
 
   return promise;
 }
 
 Nullable<ExceptionCode> HTMLMediaElement::Play() {
   BLINK_MEDIA_LOG << "play(" << (void*)this << ")";
 
   Nullable<ExceptionCode> exception_code = autoplay_policy_->RequestPlay();
 
+  if (EffectivePreloadType() == WebMediaPlayer::kPreloadNone && !src_object_)
+    pending_play_ = true;
+
   if (exception_code == kNotAllowedError) {
     // If we're already playing, then this play would do nothing anyway.
     // Call playInternal to handle scheduling the promise resolution.
     if (!paused_) {
       PlayInternal();
       return nullptr;
     }
     String message = ExceptionMessages::FailedToExecute(
         "play", "HTMLMediaElement",
         "API can only be initiated by a user gesture.");
@@ skipping 1030 matching lines @@
       // Set rate, muted before calling play in case they were set before the
       // media engine was setup.  The media engine should just stash the rate
       // and muted values since it isn't already playing.
       GetWebMediaPlayer()->SetRate(playbackRate());
       GetWebMediaPlayer()->SetVolume(EffectiveMediaVolume());
       GetWebMediaPlayer()->Play();
     }
 
     StartPlaybackProgressTimer();
     playing_ = true;
+    if (pending_play_)
+      pending_play_ = false;
+
   } else {  // Should not be playing right now
     if (is_playing) {
       GetWebMediaPlayer()->Pause();
     }
 
     playback_progress_timer_.Stop();
     playing_ = false;
     double time = currentTime();
     if (time > last_seek_time_)
       AddPlayedRange(last_seek_time_, time);
@@ skipping 739 matching lines @@
       kMostlyFillViewportBecomeStableSeconds, BLINK_FROM_HERE);
 }
 
 void HTMLMediaElement::ViewportFillDebouncerTimerFired(TimerBase*) {
   mostly_filling_viewport_ = true;
   if (web_media_player_)
     web_media_player_->BecameDominantVisibleContent(mostly_filling_viewport_);
 }
 
 }  // namespace blink