I've noticed that with some of my videos, there is an audio track that is not being played in Chrome (always the track that has the voices and foreground sound). This seems to only happen on videos with 5.1 audio, or HEVC videos. I've included the info for one of the 5.1 audio videos, which Chrome direct streams the video, but transcodes the audio to AAC
<MediaContainer size="1" allowSync="1" identifier="com.plexapp.plugins.library" librarySectionID="2" librarySectionTitle="TV Shows" librarySectionUUID="7417184e-26c5-4686-987c-11586f752f9e" mediaTagPrefix="/system/bundle/media/flags/" mediaTagVersion="1473708464">
<Video ratingKey="12268" key="/library/metadata/12268" parentRatingKey="9529" grandparentRatingKey="8499" guid="com.plexapp.agents.thetvdb://80379/9/17?lang=en" librarySectionID="2" type="episode" title="The Celebration Experimentation" titleSort="Celebration Experimentation" grandparentKey="/library/metadata/8499" parentKey="/library/metadata/9529" grandparentTitle="The Big Bang Theory" contentRating="TV-PG" summary="After more than nine years together, the gang finally celebrates Sheldon’s birthday, surprising him with a special guest (Adam West)." index="17" parentIndex="9" rating="7.7" viewOffset="138682" viewCount="1" lastViewedAt="1475047511" year="2016" thumb="/library/metadata/12268/thumb/1475047796" art="/library/metadata/8499/art/1475047797" parentThumb="/library/metadata/9529/thumb/1475047797" grandparentThumb="/library/metadata/8499/thumb/1475047797" grandparentArt="/library/metadata/8499/art/1475047797" grandparentTheme="/library/metadata/8499/theme/1475047797" duration="1143518" originallyAvailableAt="2016-02-25" addedAt="1474993805" updatedAt="1475047796" chapterSource="">
<Media videoResolution="720" id="10948" duration="1143518" bitrate="4866" width="1280" height="710" aspectRatio="1.78" audioChannels="6" audioCodec="ac3" videoCodec="h264" container="mkv" videoFrameRate="24p" videoProfile="high">
<Part accessible="1" exists="1" id="11374" key="/library/parts/11374/1474994224/file.mkv" duration="1143518" file="F:\Seeding\The Big Bang Theory\Season 9\The.Big.Bang.Theory.S09E17.720p.HDTV.DD5.1.x264-NTb.mkv" size="695573819" container="mkv" deepAnalysisVersion="1" requiredBandwidths="12732,8593,6577,6577,6577,6577,6577,6577" videoProfile="high">
<Stream id="126211" streamType="1" default="1" codec="h264" index="0" bitrate="4129" language="English" languageCode="eng" bitDepth="8" cabac="1" chromaSubsampling="4:2:0" codecID="V_MPEG4/ISO/AVC" duration="1143519" frameRate="23.976" frameRateMode="cfr" hasScalingMatrix="0" height="710" level="41" pixelFormat="yuv420p" profile="high" refFrames="9" scanType="progressive" width="1280"/>
<Stream id="126212" streamType="2" selected="1" default="1" codec="ac3" index="1" channels="6" bitrate="640" language="English" languageCode="eng" audioChannelLayout="5.1(side)" bitDepth="16" bitrateMode="cbr" codecID="A_AC3" dialogNorm="-31" duration="1143518" samplingRate="48000"/>
</Part>
</Media>
<Director id="331" tag="Mark Cendrowski"/>
<Writer id="328" tag="Chuck Lorre"/>
<Writer id="329" tag="Eric Kaplan"/>
<Writer id="1439" tag="Jeremy Howe"/>
<Writer id="468" tag="Steven Molaro"/>
<Writer id="607" tag="Tara Hernandez"/>
<Writer id="391" tag="Steve Holland"/>
<Extras size="0"></Extras>
</Video>
</MediaContainer>