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27th January 2009, 16:04 | #1 | Link |
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Join Date: Feb 2008
Posts: 7
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min-keyint functionality
My question is about the functionality of min-keyint and also its use.
Does it set the minimum distance between key frames or between I frames? In either case what would be the benefit of setting it above 1? Are there decoders that don't function properly if I frames are too close together? If the functionality is for key frames, then I am really confused as to its use. If there is a scene change, but min-keyint prohibits a new key frame, it would seem that x264 would still produce an I frame and that future P and B frames would not reference anything before that I frame. In effect it would be a key frame that just wasn't marked as such. It seems that setting min-keyint to anything other than 1 might restrict x264 in its quest for the highest efficiency. I'm just trying to get maximum coding efficiency without breaking decoder compatibility (for me, currently PopcornHour A-100). |
27th January 2009, 17:22 | #2 | Link |
Compiling Encoder
Join Date: Jan 2007
Posts: 1,348
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min-keyint is the minimum distance between IDR frames.
best explained by example: 1. frame 40 is an IDR frame 2. scenecut triggers at frame 50. if min-keyint is >10 (default 25) then frame 50 will be an I frame. if min-keyint is <=10 then frame 50 will be an IDR frame. afaik, some decoders/standards have restrictions on the distance between IDR frames i.e. meGUI's blu-ray settings has min-keyint as 2 rather than 1, this prevents consecutive IDR frames. Last edited by kemuri-_9; 27th January 2009 at 17:25. |
27th January 2009, 17:46 | #3 | Link | |
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Join Date: Feb 2008
Posts: 7
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Quote:
In my current encode with defaults for min-keyint and max-keyint, I see as many as 6 consecutive I frames (the first also being an IDR frame). It is curious to me why a decoder would be fine with numerous consecutive I frames, but be unhappy if they are marked as IDR frames. Does anyone know what the min-keyint requirements are for common decoders (PC-based, PS3, AppleTV) and how the default of 25 came about? |
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