[Request] Any Guides to FFMPEG, Transcoding, Codecs, and Metadata?

fenndev@leminal.space to Piracy: ꜱᴀɪʟ ᴛʜᴇ ʜɪɢʜ ꜱᴇᴀꜱ@lemmy.dbzer0.com – 54 points –

I have a collection of about ~110 4K Blu-Ray movies that I've ripped and I want to take the time to compress and store them for use on a future Jellyfin server.

I know some very basics about ffmpeg and general codec information, but I have a very specific set of goals in mind I'm hoping someone could point me in the right direction with:

  1. Smaller file size (obviously)
  2. Image quality good enough that I cannot spot the difference, even on a high-end TV or projector
  3. Preserved audio
  4. Preserved HDR metadata

In a perfect world, I would love to be able to convert the proprietary HDR into an open standard, and the Dolby Atmos audio into an open standard, but a good compromise is this.

Assuming that I have the hardware necessary to do the initial encoding, and my server will be powerful enough for transcoding in that format, any tips or pointers?

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oh hey I've actually done this recently so a lot of this is fresh for me. Now I had a slightly different use case than you, I had a bunch of AV1 files that wouldn't run on my pi so I had to convert them to something less GPU intensive. I was finding x265 was indistinguishable for me from AV1, and had a HUGE file size drop, close to a half or even a third. x264 had a larger file size than 265 and looked worse so I don't recommend it. I did not try VP9 once I was satisfied with 265 but you could try it out and see how it compares. My recommendation is to pick one (shorter) file and run a couple of different transforms on it till you're satisfied before trying to transform your entire library

Preserving audio and metadata is trivial, just use -c:a copy for audio and -c:d copy for metadata

EDIT: I feel dishonest not mentioning the important caveats regarding my own experiments. My files were 1080p, so the difference between codecs might be less noticeable at that resolution. It was also anime, which is similarly going to be easier to compress and be less distinct between codecs. This is why I cannot recommend x264 because if you can ruin 1080p anime it'll ruin whatever you're working with. This is why I recommend picking a sample video and spend a day running a couple test transformations on it to see what you like

Skipping the audio encode from a blu-ray will lose op out on a surprisingly large amount of space, especially with 110 source disks. I checked one of my two hour blu-ray backups. Audio will net you about nine audio tracks (english, french, etc). A single 5.1 448kbs audio track will take about 380MB of space per movie. Multiply that by nine (the number of different tracks in my sample choice) and you'll get 3420MB per disk. That means about 376GB of space is used on audio alone for ops collection. A third of a terabyte. You can save a lot of space by cutting out the languages you don't need, and also by compressing that source audio to ogg or similar.

By running the following ffmpeg command; ffmpeg -i out-audio.ac3 -codec:a libvorbis -qscale:a 3 small-audio.ogv I got my 382MB source audio track down to 200MB. Combine that with only keeping the language you need, and you end up dropping from 376GB down to 22GB total.

You can likely save even more space by skimping on subtitles. They're stored as images, so they take up a chunk of space too.

Please use Opus instead of Vorbis. Vorbis is old and had been superseded by Opus.

Since you're talking about anime, how did you solve the subtitles problem? My pi doesn't transcode fast enough but I haven't found a tdarr extension to do that automatically (nor a command)

I'm sorry my subtitles worked fine from the beginning so I don't know what to tell you. I've got a pi4 running osmc as my media center if that makes any difference.