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h.264 – key frame every X frames
Is there no Compressor forum? I couldn’t find it…unless I’m going blind.
Anyway, when exporting an H.264 Quicktime from Compresso with the intent for smaller file sizes, I achieve small file sizes by encoding Key Frames every 15 frames. Is this basically the same as mpeg compression? I’m guessing it is similar to GOP compression, but are there I, B, and P frames? My guess is, “yes,” but I want to be sure incase I have to explain this to people. I don’t want to give out incorrect information.
Thanks for your insight.
Robert J. Grauert, Jr.
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6 Replies
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[Rob Grauert] “Is there no Compressor forum? I couldn’t find it…unless I’m going blind. “
You’re not going blind. But there’s this:
https://forums.creativecow.net/forum/compressiontechniques
– Don
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Rob,
You really should get Aharon Rabinwitz’ Cow DVD, Internet Killed the Video Star https://store.creativecow.net/p/64/internet_killed_the_video_star Aharon fully explains all of the settings, such as key frames, quite nicely.
Here are a few things I learned from Aharon about key frames:
Proper setting of keyframes depends on the nature of your video. If it is fast moving and changes a lot from frame to frame, use more keyframes so that more frames are analyzed and encoding better optimized. If it’s more static, like a talking head, then use fewer keyframes.
If you have loads of fast moving action, and you have a powerful computer and a little time on your hands, you can set keyframes to zero, and every frame will be analyzed and optimized.
The subject can actually become quite complicated if you have a real mix of stuff such car racing interspersed with interviews, but this is why 2-pass and 3-pass encoding was developed.
David Roth Weiss
Director/Editor
David Weiss Productions, Inc.
Los AngelesPOST-PRODUCTION WITHOUT THE USUAL INSANITY ™
A forum host of Creative COW’s Apple Final Cut Pro, Business & Marketing, and Indie Film & Documentary forums.
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Thanks Dave. I’ll save up for that DVD. I got a creative cow DVD for Color and was very satisfied with that, so im sure the one you suggested will be just a good.
Robert J. Grauert, Jr.
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Yes Rob, it is exactly like mpeg because H264 is Apples fancy name for mpeg4
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Hi,
Today we can consider MPEG~2 like part of a broadder format that is MP4 but that’s all.
MP4 do not even use the term GOP.
The format is based in grups of pictures of course but is a kind of “adaptative” GOPs.
You can not decide ~different with MPEG/2~ the GOP structure.
is the compressor who decide so.
The same happens with the macroblocs structure. MPEG~2 uses always 16×16 pixels blocks, while can use many different macroblock sizes, being the smaller 4×4 pixels.
Basically the data rate that you choose will determin the GOPs and Macroblock structure.
I think that is risky to set any Key Frame number. You may be forcing the compressor to set too many or too litle “I” frames.
I think a good software will analize the movie properly and will set the optimal amount of key Frames in a double pass compression.
So far the test I’ve done had always work perfect letting the key Frames in Auto. And this way I’ve got the smaller files too.
There is very good info in Wikipedia just typing “h264”.
And you will find few interesting thing if Google “h264 GOP”.
Cheers,
rafael
PS> Sorry for my writing~worst than the usual~ I’m typing in a chines PC with a wilde keyboard.(and here some clips for the friends: https://www.vimeo.com/2694745 )
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Thank you. This is very good and useful information…as usual from this website.
Robert J. Grauert, Jr.
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