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Key frames and H.264. Off by 1/1000
I am working in Final Cut 6.0.5 and need to export an H.264 video at 15fps with a keyframe every 15 frames. We are then embedding this video into a custom player that relies on these key frames for navigation functionality. The original sequence is 29.97, and I’m using the Export>Quicktime Conversion options set the frame rate and key frames.
When it outputs, the keyframes should be every second on the second, but instead they are coming out every 1.001 seconds. So, the sequences goes: 1.001, 2.002,3.003 and so on. It’s not a big deal in the fist few minutes, but this is a two-hour long video, and as it progresses, the key frames get farther and farther off.
Does anyone here have any idea why this is happening, and more importantly, how to fix it? We don’t necessarily need every key frame to be at x.000, but they do need to be one second apart.
Thanks!
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6 Replies
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You might export a self-contained QT using current settings, and then use Compressor to encode the file. QT Conversion has issues now and then.
John
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We tried exporting through Compressor, but I was not successful inserting keyframes every second in an h.264 file. Do you know how to do that?
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Take any of the H264 clips and delete the TC track (Clip properties) and see how its works.
rafael -
Thank you! I had read that NTSC was offset from 30fps by 1/1000, but I didn’t know what to do with that information. That explanation is just what I was hoping for!
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So, that solution worked beautifully, except the key frame for every 8th second is off. We’re speculating it’s because 1/15 = 6.666666666666, repeating and there’s some crazy math that throws it off on the 8th second, but that’s just a guess. We found a way to work around it in our player, but we’re still wondering what’s going on. Any ideas?
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I gave up on this and didn’t see your reply until just now.
The answer to your “why” question is both. It’s a highly specialized situation and there are folks here trying to get it perfect. It would be great if it all worked out that way, but I remain completely out of ideas. Thankfully, this problem was solved through the magic of the programmers.
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