When I limit BW, Plex Transcodes Unexpectedly

[ElGordito]

Okay, I can validate that deep analysis gives us the requiredBandwidths attribute needed to keep the server from transcoding when the needed bandwidth is close, but not over the available bandwidth, as identified by @pshanew:

@pshanew

The original file has gone through deep analysis and has more firm bandwidth requirements defined:

<Part accessible="1" exists="1" id="28180" key="/library/parts/28180/1575840221/file.mp4" duration="5868029" file="/media/exfat/Movies/13 Going on 30 (2004) - BD.mp4" size="645613876" audioProfile="lc" container="mp4" deepAnalysisVersion="4" has64bitOffsets="0" optimizedForStreaming="0" requiredBandwidths="961,895,895,895,895,895,895,895" videoProfile="main">

The second file does not appear to have been deeply analyzed yet, so PMS is relying on the “two times the average bitrate” algorithm to determine bandwidth requirements:

<Part accessible="1" exists="1" id="28187" key="/library/parts/28187/1575845904/file.mp4" duration="5701800" file="/media/exfat/Movies/50 First Dates (2004).mp4" size="627670762" audioProfile="lc" container="mp4" has64bitOffsets="0" optimizedForStreaming="0" videoProfile="main">

Note the missing “deepAnalysisVersion” and “requiredBandwidths” parameters in the second list.

And it does override the default “double” requirement as identified by @hokierulz.

@hokierulz

This Plex article is very useful. Note that in their example a 3.5 Mbps average video spikes up to 10 Mbps in an action scene. It goes on to state that Plex assumes a 2x average bitrate unless a deep analysis has been performed (e.g. a 50% overhead allowance isn’t sufficient.) Particularly pay attention to the very informative “So how does Plex handle it” section. The buffer size of your client can make a big difference in the actual overall bitrate required.

The key here has to be the “requiredBandwidths” attribute in the individual media xml file and the “Deep Analysis” required to get that attribute. It allowed me to understand why two videos encoded by the same encoder using the same bitrate, resolution and audio would be acted on by the server so differently (one direct played one transcoded).

I hope this thread helps others and thank you to all who chimed in.

I love this hobby!!!