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720 60p
I know I’ve seen a number of postings regarding 30p and 60p, however I am still having trouble wrapping my head around what 60p really is…so I apologize for posting this subject again. I am just trying to keep myself educated.
I recently received some press junket footage that was shot in 720 60p. I posted it in Avid MC in a 720 60p project with no problem. I then, to my surprise, down converted the sequence and dropped it into a SD 29.97 sequence and it played out fine. It went to tape with no problems at all. My question is how is this possible? If my footage is shot in 60p and I dropped it into a 29.97i sequence, shouldn’t my 60p footage play out at a different speed? You have double the frames than a SD sequence correct?
Second question: Why would you want to shoot in 60fps or 30fps? We use Sony EX3s and I would like to use this format if it is beneficial. I appreciate any explanations anyone can offer.
Big Thanks!
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18 Replies
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[Aaron Nowakowski] ” I then, to my surprise, down converted the sequence and dropped it into a SD 29.97 sequence and it played out fine.”
That’s because it’s supposed to. 60p is built to play at normal speed in a 29.97 timeline. As with interlaced which plays 60 fields per second, 60p plays at 60 frames per second, or if you like, 2 complete pictures (like a photograph) every 30th of a second.
[Aaron Nowakowski] “Why would you want to shoot in 60fps or 30fps”
Shooting 60p has more temporal resolution which means with 60 complete pictures every second there’s less motion blur for things such as sporting events or anything that moves fast. Progressive shooting is part of the “film look” that is all the rage in video production these days, along with 30p and 24p. It’s strange the way people perceive film quality in different parts of the world. In North America people relate the interlaced look to television and news broadcast, the everyday realism. Anything but dramatic storytelling. In Japan, it’s the exact opposite. There the viewer associates the video look as dramatic storytelling.
– Don
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So then what is physically happening when you over or undercrank? I always understood that as changing the amount of frames per second?
Thank you for the help Don!
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[Aaron Nowakowski] “So then what is physically happening when you over or undercrank?”
Beats me. I suspect that there’s a flag in the 720 60p stream that instructs an NLE to play the video at normal speed. Or there are flags in the overcrank stream but not in the 60p streams. The undercrank mode is pretty simple to figure out. If you remove frames from normal video and jam together whats left it’s going to look speeded up.
– Don
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Thanks for taking the time to help out Don. It will be interesting to see if anyone else has any thoughts on this.
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The Panasonic Varicam, as its name implies, was the first “variable speed” video camera, whiuch while imitating the variable speed function of a film camera did so in a slightly different manner.
The ability to “undercrank”, essentially meaning to shoot at frames rates lower than normal, meant repeating frames, such that for example if you shoot at 10 frames per second each frame is repeated for six frames (as the camera always records 60 frames per second – called 60p).
At so called “normal speeds” of either 24 or 30 frames per second the camera duplicates frames either in a 2:3 cadence (like teleine) at 24p or by repeating every frame twice at 30fps. At all frame rates that require repeating frames the camera marks the first of each set of repeats with an “A’ frame in the user bits. This way if you want to recreate an undercranked effect, or a 24 or 30 fps timeline, your software can “pull” only the discreet frames out of the recording and not the duplicates.
Overcranking is made possible by playing pack the frame rates higher than “normal” (either 24 or 30) at the normal frame rate. For example if you shoot at 60p and play back at 30p the slomo effect will be 2x. If played back at 24p the slomo effect is higher at 2.5x. It is also possible to double print the 60p and have somethink like (but not exactly the same as) 120fps. The cameras have the capacity to make that many frames but are unable to record them.
Cameras since the Varicam have copied these techniques and now there are models that can write 1920×1080 at rates as high as 60p.
Hope this helps!
JS
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..I use 720 60p in my EX3 when shooting sports or some action clips….to me is an option to overcrank … “slowing” the frame rate of the 60p clips in Vegas gives me nice “slo-mo” results….
this is a little example, what do you think ?? (2nd. part of the video…):
https://www.youtube.com/watch?v=nA3TZovGWo4
…my 2 cents…
Enrique Orozco R.
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Thanks for sharing Enrique, the overcranking looks clean.
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As far as I know, shooting “overcrank” flags the footage as whatever speed your camera is set at. For instance, say you’re shooting 720p24, and overcranking to 60fps. The file that is being created is a true 24p file; it’s simply being recorded onto the card faster than real time. I don’t know this for sure, but i believe that the advantage of shooting overcrank as opposed to simply shooting at 60p and slowing down in post is compression. Remember, the XDCAM-EX format is 35 mbps, regardless of resolution or framerate. Theoretically, overcranked footage plays back at the same bit rate as footage recorded at the normal rate. Therefore, the camera has to process data much faster than 35 mbps when overcranking, which explains why you can only overcrank to 60fps while shooting 720p (and why Sony doesn’t recommend using non SxS media when overcranking).
On the other hand, if you shoot footage at 60fps, the bit rate is still 35 mbps, but the codec has to encode many more frames per second with this same amount of data, resulting in more compression per frame. While you can actually achieve decent results by slowing down 60p footage to 24 fps, the overall quality will be better if you overcrank while shooting.
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Another thing about 60p is that it can be used to create a true 29.97 interlacing. For this reason I use it when I know my final product must be standard definition, 29.97 interlaced. Being a progressive format, it downscales much better than, say, 1080i, and doesn’t result in a juttery look like 30p does. Personally, I can’t stand 30p…if I want to shoot progressive I’ll shoot 24p. That way, I can emulate a true film look, and non-progressive monitors get the benefit of a 3:2 pulldown, just like any movie. Also, DVD compression works much better with true 24p footage, which can be important when encoding content that is 2+ hours on a single-layer DVD.
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