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Old 21st November 2008, 15:20   #1  |  Link
Comatose
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24p -> 24000/1001?

How? Is there some secret method, or is it just assumefps(24000,1001)?

Which brings me to the question... why do they still master at 24 fps or 30 fps? It seems rather stupid when the final FPS will always be 24000/1001 or 30000/1001.
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Old 23rd November 2008, 03:26   #2  |  Link
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Are you sure you really really have actual 24p? Because 23.976 is often called 24p, though technically it is not.

24p is the frame rate for film (real film), which typically has matching audio at 48048Hz. This is because American TV shows film at 23.976, slightly slower like 29.97, so the audio can be played back at 48000Hz to match.

Note that with AssumeFPS it doesn't adjust the audio, so you'd either want to AssumeSampleRate(48000) if you have 48048Hz audio, or otherwise SSRC(48000) to sync up the audio. If you really want to do that.
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Old 23rd November 2008, 03:52   #3  |  Link
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are you sure about the 48048Hz audio? i have some .ts streams (1920x1080i@30000/1001) and they're 48000Hz on the dot.
even dvds I've worked with are 48000Hz...
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Old 23rd November 2008, 09:24   #4  |  Link
IanB
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24000/1001 ~ 23.9760239760...

24000/1001 * (1001/1000) = 24.0

48000 * (1001/1000) = 48048
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Old 23rd November 2008, 13:12   #5  |  Link
Comatose
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Big Buck Bunny is 24p with 48000Hz audio. Or at least that's what the MKV ended up with when I dropped the 720p H.264 MOV into mkvmerge.
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Old 24th November 2008, 03:17   #6  |  Link
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Unless you are filming with a real film camera (i.e. in the +$80,000 range), there's almost no way/reason you would have true 24p and even need to think about 48048Hz. If you have a TV source and you inverse telecine, or a "24p" camera, 24000/1001 is the rate you should use (and get). No need to convert from 23.976 to true 24p. The film TV rate in the US is 24000/1001. And yes, they do master at that rate (on DVD/Blu Ray). Sorry, I missed your question on mastering on my first read.

Edit: They may master the studio original at 24p/48048Hz (or a higher sample rate with similar proportion). This is probably because the whole system is built on it and it's hard to teach an old dog new tricks. But such a slight slowdown is in no way noticeable to the viewers, so it doesn't really matter. The PAL speedup, however, is noticeable.
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Old 24th November 2008, 15:20   #7  |  Link
Comatose
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Quote:
No need to convert from 23.976 to true 24p.
Helloooooo? I didn't convert. It was 24p (not 24000/1001) with 48000Hz audio.
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Old 24th November 2008, 15:58   #8  |  Link
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Well then every 1000 frames (41 2/3 seconds), there will be a little jerkiness with ChangeFPS(24000,1001).
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Old 24th November 2008, 16:07   #9  |  Link
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I don't see why using assumefps is not fine for this issue... Assumefps(24000,1001,true) will change the framerate and sync the audio accordingly, without introducing any jerks.
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Old 24th November 2008, 23:33   #10  |  Link
IanB
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Quote:
Originally Posted by Comatose
the MKV ended up with when I dropped the 720p H.264 MOV
It is perfectly acceptable for someone to encode a 24.0 fps video stream with a 48000 Hz audio stream. It is just a little unexpected these days. Stupid NTSC 30000/1001 has pervaded the world, learn to live with it.
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