I usually use the the KeyInt 250 default x264 setting when encoding videos for Blurays as it saves about 1 GB a disc compared to KeyInt 100 for 720p 50fps videos. It's no longer Bluray compliant when I do that but I've not seen a player that can't play it. When playing the video back on MPC-HC on my PC the seek time when clicking on a random time in the video is about a second or so but I didn't notice any delay on a Bluray played on a physical Bluray player when using the fast forward and rewind buttons on my remote control.
Why isn't there a delay on the physical Bluray player? If there's no delay then is there any reason why I shouldn't use a really high KeyInt setting to lower the file size?
What is the maximum KeyInt setting I can use?
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Thanks. I was told for a 2 second GOP you could use KeyInt 100 and it would be Bluray compatible. As mentioned here: https://forum.doom9.org/showthread.php?t=154533
I'm using a much higher KeyInt anyway for a Bluray disc (I know it's not Bluray compliant but it still plays fine).
What's the maximum KeyInt setting I can use? Any reason why I shouldn't use it?
Last edited by VideoFanatic; 22nd Apr 2018 at 18:59.
You only need BD compatibility if you're authoring a physical BD disc.
If you're just playing files off USB or non authored disc, usually the restrictions are much more relaxed. Then it depends on the particular model, but most can play typical settings with L4.1 . Some will still exhibit stutter and seek issues with longer GOP's or many b-frames or >4 reference frames . Some can play anything.
The compression benefit of higher keyints diminishes anyways as you go higher. 250 is already pretty high for most content. I find ~4 seconds to be a good sweet spot.
You are allowed to use 2 seconds on Blu-Ray if the --vbv-maxrate is <= 15000.
But as you found out most players don't really care unless you go too extreme where seeking makes them crash. Same with bframes. Blu-Ray allows not more than 3 consecutive ones but it doesn't really matter for most decoders.
I usually use about a keyframe interval around 50 myself. That gives a good balance between seekability and compression. I don't care about blu-ray compatibility. You can the interval as long as you want. But imagine how long it will take to seek to a random spot in the middle of a 2 hour movie encoded as a single GOP. The decoder has to go back to the first frame and decompress every frame up to the one you requested. It will take forever off optical media. If you're set for fast seeks you'll only be able to seek to the first frame of the movie.
The only time I've had issues with high intervals is when cuttong media to remux. As you must cut on a I frame if you have a GOP of 250 you may have 9-10 seconds of extra material and some av sync. Same applies when inserting chapters. For just straight playback most players dont care on playback, just may act funny when Fast forwarding etcif all else fails read the manual