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h264 -maxrate is seriously degrading video quality


noclip
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Hi there! First of all, I'd like to thank everyone who contributes to this project. It's awesome!

 

I'm having a transcode quality issue with a certain set of files that seems to be related to the value emby chooses for the -maxrate option of the h264 codec. Here's my evidence:

 

I took the ffmpeg transcode command from the (attached) server log and ran it locally (I removed the segment stuff and limited duration with -t, but no changes other than that). Playing the result with a local media player resulted in the same aggressive artifacting I was seeing in my browser.

 

Then, I ran the exact same transcode without "-maxrate 1165053", and boom, no visible artifacts. The bitrate is 2x larger than the original source (not really sure why that's the case), but I run everything over LAN and I have a lot of throughput headroom to spare, so I'd really like to make the trade-off for quality. Is there any way I can affect what emby chooses for maxrate?

 

I've done some poking around and found this thread (https://emby.media/community/index.php?/topic/36226-transcode-quality-degradation-maxrate/), but not much info in there. Running server ver  3.2.15.0 on Ubuntu.

 

Thank you in advance!

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hi @@noclip, thanks for the report. this is actually an extreme case, as it is low bitrate 720p, and we use the source bitrate as the output value. But I'll look and see how we can raise it here. thanks.

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Thanks for the quick reply! Do you have an understanding of why the source quality is so much better at a lower bitrate? In other words, why do we need 2x the bitrate of the source to avoid artifacts? And why does resolution make a difference?

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