A friend streamed a movie last night and I don’t understand why it transcoded:
My understanding is that Plex for Vizio supports HEVC. I do have a stream limit of 4 Mbps, but the original bitrate is only 2047 kbps.
This “original bitrate” can be very misleading. This number is a very simplistic “average” of file size, divided by run time. The bitrate of video is usually not a constant.
It is certainly possible that the actual bitrate of parts of this movie does exceed your limit of 4 mbps.
That’s why Plex does perform an in-depth analysis of the file to determine the actually required bandwidth to stream that file (if you let it).
You can find the result of that analysis in the Plex media info XML, in the XML property requiredBandwidths.
Here is an example of a regular 1080p movie. Notice the difference between the numbers in bitrate and requiredBandwidths. The multitude of numbers in requiredBandwidths is due to differently sized network buffer memory in the various client types. The smaller that buffer, the higher the actually required bandwidth to stream a file without hiccups.
You can bet that smart TV’s have rather small buffer sizes, so for them you will need to look at the first or second number in requiredBandwidths:
<Stream id="2363858" streamType="1" default="1" codec="h264" index="0" bitrate="5411" language="Englisch" languageTag="en" languageCode="eng" bitDepth="8" chromaLocation="left" chromaSubsampling="4:2:0" codedHeight="1088" codedWidth="1920" colorPrimaries="bt709" colorRange="tv" colorSpace="bt709" colorTrc="bt709" frameRate="23.976" hasScalingMatrix="0" height="1080" level="40" profile="high" refFrames="4" requiredBandwidths="10881,9163,8105,7210,6849,6551,6178,6178" scanType="progressive" width="1920" displayTitle="1080p (H.264)" extendedDisplayTitle="1080p (H.264)"> </Stream>
So much for the theoretical reason of a transcode.
What the actual reason for the transcoding was, can be seen in “debug” server logs.
Very interesting:
<Stream id="692218" streamType="1" default="1" codec="hevc" index="0" bitrate="2047" bitDepth="8" chromaLocation="left" chromaSubsampling="4:2:0" codecID="hvc1" codedHeight="800" codedWidth="1920" colorPrimaries="bt709" colorRange="tv" colorSpace="bt709" colorTrc="bt709" frameRate="23.976" height="800" level="120" profile="main" refFrames="1" requiredBandwidths="5257,4357,3349,2896,2896,2896,2896,2896" streamIdentifier="1" width="1920" displayTitle="1080p (HEVC Main)" extendedDisplayTitle="1080p (HEVC Main)">
So, it does appear you are correct: the bandwidth requirements are possibly higher than 4 Mbps.
Thanks Otto for expanding my knowledge!
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