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+--- Thread: Custom transcode profile ? (/t-custom-transcode-profile)
Custom transcode profile ? - cosmicvoyager - 2024-07-09
Hi,
My setup supports HEVC encoding for transcoding media but in my opinion the proposed transcode quality profiles do not enable taking advantage of the efficiency of HEVC. For instance, the lowest bitrate for 1080p streams is 10 Mbps, while 1080p HEVC files already look good at 4Mbps. Is there any way to address this ?
Thanks !
RE: Custom transcode profile ? - TheDreadPirate - 2024-07-09
I'm assuming you are talking about the "Quality" selector. That doesn't actually force the stream to be that bit rate. It only sets the maximum allowed bit rate. If the video happens to be lower than, in your example, 10Mbps than the video will direct play (assuming it is compatible with the client).
The resolution in the quality selector also doesn't really change anything.
When Jellyfin is converting from codec to another during transcoding, it will apply some loose math to account for changes in encoding efficiency. It will take the original video bit rate and increase or decrease the bit rate appropriately.
https://github.com/jellyfin/jellyfin/blob/5ef76a5e31d7cb09e8daf31ca819a6e206b5149a/MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs#L2491C31-L2491C57
RE: Custom transcode profile ? - cosmicvoyager - 2024-07-09
Thank you for your answer, it shed some light. But let's imagine the following case : 1080p source encoded in H264@8Mbps. Using the lowest 1080p preset, the source will play without transcode. Let's imagine that my connexion bandwidth would only allow me to stream at 4Mbps. My only option is to select a 720p resolution while in theory I could get a 1080p stream in HEVC @ 4Mbps. Did I miss something ?
RE: Custom transcode profile ? - TheDreadPirate - 2024-07-09
The resolutions listed in the quality selector are, essentially, meaningless. If you selected 4Mbps you would probably still get 1080P. If you click on the gear and click on Playback Info it will tell you what the transcode resolution is.
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EDIT: It appears this behavior has changed since 10.8. It does, in fact, set the transcode resolution now.
RE: Custom transcode profile ? - TheDreadPirate - 2024-07-09
Another revision to my statement. It doesn't appear that the resolution limit in the quality selector is strict. At 6Mbps I am still getting 1080P transcodes. But 4Mbps does drop down to 720P.
RE: Custom transcode profile ? - cosmicvoyager - 2024-07-10
Indeed, 720p6Mpbs still gives 1080p resolution, but 720Mp@4Mbps gives 720p. I think with HEVC we could go down to 1080p@4Mpbs but the difference to 6Mbps in terms of bandwidth is not huge. Thanks for the help
RE: Custom transcode profile ? - TheDreadPirate - 2024-07-10
The devs confirmed that the resolution in the quality selector is meaningless and are discussing just removing it. There is code on the server that decides the ideal resolution for the bit rate selected. The only "customizable" option is the max allowed transcode resolution.