6 ms·

Because audio for 23.976fps film is playing at the same speed as 29.97fps video. Which is really interlaced video at 59.94 fields per second. 3:2 pulldown is us

Because audio for 23.976fps film is playing at the same speed as 29.97fps video. Which is really interlaced video at 59.94 fields per second. 3:2 pulldown is used to synthesize extra video frames to transfer to NTSC video so for a given instance of time, for every 4 frames of film you get 5 frames of video. (23.976/29.97 = 4/5) The instance of time remains unchanged so the audio is playing back at the same speed. This is all inherited from the CRT days before progressive video playback on flatscreens, and the video fps was tied to the local electrical frequency (50 Hz in Europe vs 60 Hz in USA / Japan) which is how the CRT timings were derived. Coincidentally PAL video plays back at 25fps, to convert film to PAL they just speed it up from 24 to 25fps, audio and all, which is why if you watch a Euro DVD release of the same film all the actors sound like they just ingested helium before the scene because the audio is playing back ~4% faster. This was largely fixed with Blu-Ray as films play back at their native rate[1] on progressive displays but our European friends who have only seen films on VHS/DVD or TV and not in the theatre or Blu-Ray have been done a disservice, because the video and audio is sped up on playback and not as the director intended it to be shown. [1] A notable exception is some unscrupulous distributors abroad release shitty PAL 25fps Blu-Rays of films which are simply upscaled PAL DVD versions that they then market as Blu-Ray but are worse than DVD quality but at marked up prices. This is more common than you think. Official releases from the studios are encoded at 23.976fps on the disc. TV shows shot on PAL video (native 25fps) will always play back at 25fps.

gsich 4y ago
Pitch correction exists.
- deleted 4y ago
  [deleted]
- garaetjjte 4y ago
  It's not straightforward and might introduce artifacts.
  - lecoyote418 4y ago
    There are algorithms that are better than others. For example, ffmpeg's pitch correction using "atempo" filter (WSOLA) is average and might present artifacts depending on source audio. ZTX (was Dirac) is another algorithm that's commercial and pretty much artifact free. Btw, sound studios responsible for the 24-25 pitch shift often have the possibility to process the pitch shift on separate dialogue, music and effects tracks, limiting even more the artifacts in the converted output.
xattt 4y ago
Frame rate screw-up story time: Around 2009, my street flooded and I decided to record it and sell it to a local news station. I had one bite and I took my camera over to the TV station (CTV). When I got there, I was beyond disappointed that (1) they didn’t have an HDV player and that (2) I forgot my FireWire cable. I rushed home, imported/exported it in FCP, burnt it to a DVD and rushed back. In the rush, I forgot to ensure the right frame rate was set. When I got there, the techs were able to ingest it no problem, but my heart dropped when I noticed the import rate on a little VFD was 1080/50i. Fortunately, it worked out and when my video aired, it looked like it was from an international source because of the pulldown. I ended up getting a cheque for $135 for 8 broadcasted seconds of video and a day’s work of rushing back and forth. I’ve extrapolated it to be my most valuable piece of work at about $60,000 per hour.
at_a_remove 4y ago
That PAL speedup drives me nuts. I thought I was losing my mind the first time I noticed it. Nobody else did. Eventually I reasoned out why and found the appropriate name for the phenomenon. You can get pitch-shifters, but on DVD players, the only ones with this feature I can find happen to function as karaoke machines.
yellowapple 4y ago
On the topic of playback rate/pitch fuckery, Janet Jackson's "Rhythm Nation" was sped up ever so slightly after recording (as was sometimes done at the time to make the music sound more "exciting" or "intense"), and that's one of the hypotheses for why playing it interferes with laptop hard drives: the dominant E frequency/pitch got shifted up to somewhere slightly sharp of E (but not quite E#), which just so happens to be closer to some drives' resonant frequency.
toast0 4y ago
> This is all inherited from the CRT days before progressive video playback on flatscreens, and the video fps was tied to the local electrical frequency (50 Hz in Europe vs 60 Hz in USA / Japan) which is how the CRT timings were derived. I'll have you know, there were CRTs that did progressive scan too. Early HDTVs were CRTs, before flat screen TVs got big. Plenty of PAL CRTs can accept NTSC at 60Hz on a 50Hz supply too, of course. It's nice to tie the supply and video rates together to reduce interactions between the two rates.
grouchomarx 4y ago
>Because audio for 23.976fps film is playing at the same speed as 29.97fps video. Which is really interlaced video at 59.94 fields per second. 3:2 pulldown is used to synthesize extra video frames to transfer to NTSC video so for a given instance of time, for every 4 frames of film you get 5 frames of video. would you explain this to me like I'm 5?
- erik 4y ago
  NTSC television video is interlaced. First you draw the even lines of the image, then you draw the odd lines. Each set of lines is called a field. Originally NTSC was 60 fields per second, based on the 60hz frequency of the North American power grid. 60 interlaced fields per second is pretty similar to 30 frames per second, but is not the same thing. The interlaced signal refreshes twice as quickly, but with half the vertical resolution per refresh. When colour was added to NTSC, the frequency was shifted to 59.94 fields per second. Movies shot on film are filmed at 24 frames per second. To convert a 24fps film to 60 field per second video, something called a 2:3 pulldown is used. The wiki explanation for how this works is pretty good: https://en.wikipedia.org/wiki/Telecine#2:3_pulldown https://en.wikipedia.org/wiki/Telecine#2:3_pulldown A 2:3 pulldown on 24fps film matches the 60 fields per second of the original black and white NTSC signal, but is slightly off for colour NTSC. The original article talks about how this can lead to problems like audio desync in production workflows. Digital cameras offer the option to capture at 23.976fps. When you apply a 3:2 pulldown to 23.976fps video, you get an interlaced 59.94 fields per second video.
  - grouchomarx 4y ago
    Fantastic. Thank you

gsich 4y ago

Pitch correction exists.

deleted 4y ago
[deleted]
garaetjjte 4y ago
It's not straightforward and might introduce artifacts.
- lecoyote418 4y ago
  There are algorithms that are better than others. For example, ffmpeg's pitch correction using "atempo" filter (WSOLA) is average and might present artifacts depending on source audio. ZTX (was Dirac) is another algorithm that's commercial and pretty much artifact free. Btw, sound studios responsible for the 24-25 pitch shift often have the possibility to process the pitch shift on separate dialogue, music and effects tracks, limiting even more the artifacts in the converted output.

xattt 4y ago

Frame rate screw-up story time: Around 2009, my street flooded and I decided to record it and sell it to a local news station. I had one bite and I took my camera over to the TV station (CTV). When I got there, I was beyond disappointed that (1) they didn’t have an HDV player and that (2) I forgot my FireWire cable. I rushed home, imported/exported it in FCP, burnt it to a DVD and rushed back. In the rush, I forgot to ensure the right frame rate was set. When I got there, the techs were able to ingest it no problem, but my heart dropped when I noticed the import rate on a little VFD was 1080/50i. Fortunately, it worked out and when my video aired, it looked like it was from an international source because of the pulldown. I ended up getting a cheque for $135 for 8 broadcasted seconds of video and a day’s work of rushing back and forth. I’ve extrapolated it to be my most valuable piece of work at about $60,000 per hour.

at_a_remove 4y ago

That PAL speedup drives me nuts. I thought I was losing my mind the first time I noticed it. Nobody else did. Eventually I reasoned out why and found the appropriate name for the phenomenon. You can get pitch-shifters, but on DVD players, the only ones with this feature I can find happen to function as karaoke machines.

yellowapple 4y ago

On the topic of playback rate/pitch fuckery, Janet Jackson's "Rhythm Nation" was sped up ever so slightly after recording (as was sometimes done at the time to make the music sound more "exciting" or "intense"), and that's one of the hypotheses for why playing it interferes with laptop hard drives: the dominant E frequency/pitch got shifted up to somewhere slightly sharp of E (but not quite E#), which just so happens to be closer to some drives' resonant frequency.

toast0 4y ago

> This is all inherited from the CRT days before progressive video playback on flatscreens, and the video fps was tied to the local electrical frequency (50 Hz in Europe vs 60 Hz in USA / Japan) which is how the CRT timings were derived. I'll have you know, there were CRTs that did progressive scan too. Early HDTVs were CRTs, before flat screen TVs got big. Plenty of PAL CRTs can accept NTSC at 60Hz on a 50Hz supply too, of course. It's nice to tie the supply and video rates together to reduce interactions between the two rates.

grouchomarx 4y ago

>Because audio for 23.976fps film is playing at the same speed as 29.97fps video. Which is really interlaced video at 59.94 fields per second. 3:2 pulldown is used to synthesize extra video frames to transfer to NTSC video so for a given instance of time, for every 4 frames of film you get 5 frames of video. would you explain this to me like I'm 5?

erik 4y ago
NTSC television video is interlaced. First you draw the even lines of the image, then you draw the odd lines. Each set of lines is called a field. Originally NTSC was 60 fields per second, based on the 60hz frequency of the North American power grid. 60 interlaced fields per second is pretty similar to 30 frames per second, but is not the same thing. The interlaced signal refreshes twice as quickly, but with half the vertical resolution per refresh. When colour was added to NTSC, the frequency was shifted to 59.94 fields per second. Movies shot on film are filmed at 24 frames per second. To convert a 24fps film to 60 field per second video, something called a 2:3 pulldown is used. The wiki explanation for how this works is pretty good: https://en.wikipedia.org/wiki/Telecine#2:3_pulldown https://en.wikipedia.org/wiki/Telecine#2:3_pulldown A 2:3 pulldown on 24fps film matches the 60 fields per second of the original black and white NTSC signal, but is slightly off for colour NTSC. The original article talks about how this can lead to problems like audio desync in production workflows. Digital cameras offer the option to capture at 23.976fps. When you apply a 3:2 pulldown to 23.976fps video, you get an interlaced 59.94 fields per second video.
- grouchomarx 4y ago
  Fantastic. Thank you