New Transcoder: Bitrate Limit Tied to Bufsize, Not Maxrate

Plex Media Server Plex Pass Betas
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With the new transcoder, when setting the server’s max “Limit Stream Remote Bitrate”, it seems to correlate with the bufsize rather than the bitrate itself. For example, if the max remote bitrate is set to 40Mbps, ffmpeg parameters set the bufsize to 37090K, but the maxrate 18545K. Also, if I set the quality on the client itself, I also see similar results. If I set the quality to 20Mbps, the bufsize is 21334K and the maxrate is set to 10667K. So, in summary, the bitrate is actually half of what is expected. I understand why the bufsize is double the maxrate as that is a good practice, but quality options should dictate the maxrate, not the bufsize. So, for example, if I set the stream quality to 20 Mbps on my client, the maxrate should be equal to 20Mbps minus the audio bitrate, and then the bufsize should be double whatever that number is. This is how major streaming services do it as well. When they advertise “25Mbps suggested internet speeds for 4K content”, the average bitrate is 25Mbps with spikes up to 50Mbps.

Also, while I’m here I really like the new transcoder overall! Look forward to seeing this fully implemented in stable.

EDIT: I want to come back to this and say that this also appears to be a thing on the previous transcoder as well… I assumed this was a bug or error with the new transcoder. I’m going to keep this post up as I think this needs to be fixed or at least reevaluated because the client quality options are very deceiving.

Server Version#: 1.43.0.10231
Player Version#: 4.152.0 (Plex Web)

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Thanks for your testing!!! I wondered about this as I have my remote rate set to 40 and I never see a transcoded rate above 22mb. I also expected to see 40mb streams when I set this limit.

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This makes a lot of sense now why the quality options on my clients doesn’t match with what my server dashboard says. This should be fixed because a 50% difference in bitrate compared to the selected quality option is really deceiving and effectively caps the maximum quality to 10-12Mbps on the new Plex experience clients since their quality options cap at 20Mbps.

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