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Best way to encode with H.264 HD from FCP
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Key Frames has me a little confused…I have seen better results for some video with less key frames (i.e every 150 frames) than with more (every 5 frames). Any way of narrowing this down or isa it just trial and error.
Oh how would I rerender a DVCProHD file in FCP? In teresting though because I have noticed that when I encode staright from FCP I get audio lag…not cool!
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Every 5 frames is ‘wrong’ (when I saw that you were using that seeting in an earlier post I assumed it was for every 5 seconds) – a general rule of thumb is to set keyframes to be 10 x your frame rate, so at 30fps there should be a keyframe every 300 frames.
Modern codecs are very good at inserting keyframes when there’s enough of a ‘scene-change’ to warrant one.
Inserting more frequent keyframes (especially once every 5 frames) usually just ends up making a much bigger file, with a much higher datarate and without too much improvement in picture quality.
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Danny’s correct.
Here’ some more info.
Modern codecs will insert keyframes on edit points (scene change). Those are often referred to as “natural” key frames. There’s also setting a keyframe rate, often referred to as “forced” key frames.
Those “forced” keyframes can become important if you have shots that go on for a bit without an edit point. The image can gradually look worse as it gets farther away from a keyframe so there can be value to using forced keyframes.
Sometimes you can see keyframe “breathing” though. A sudden visual increase in quality for one frame (the keyframe) which can be more or less obvious depending on codec, frame rate, content.
10x the frame rate for forced keyframes is a good rule of thumb as Danny mentions but what one may chose might depend on content. Something with lots of fast action/motion might warrant more a higher forced keyframe frequency.
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Good stuff guys! yeah, I can’t wait to try encoding with KF every 300 frames! Will let you know how it goes…
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Not much changed in the picture quality, but the file size did decrease somewhat, which is a good thing. I think I found a sweet spot at keyframes = 150.
Under QT video size settings, what is the difference between these two settings?
HD 1920×1080 16:9 and 1920×1080 HD
Doesn’t make much sense…?
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