Can someone explain in plain english the difference between pf24, pf30, f24, and 60i?

[Daniel Webb]

Ok so I have a basic understanding of these. I understand that f24 is 'real' 24p where as pf 30 is 60i cut in half or something and pf 24 is artificially adjusted from 60i to 24p. but can someone give me a plain english explanation of what each of these modes strengths and weaknesses are and what I should be shooting in the majority of the time? It seems that alot of people prefer the native 24p but it would seem that 30p might be a better option for handling motion? Any input would be greatly appreciated.

BTW my camera is a Canon Vixia HF S200. I will be doing most of my editing in sony vegas platinum suite 10. I am looking to do many different things with my video, from putting it on youtube to burning blu rays, to burning avchd dvd's and mostly streaming the content from a home nas to a network media player.

[Predrag Vasic]

Here is my attempt at translating all this into plain English.

Your Vixia (HF-S200) is a great camcorder. One of its rather unique features is its genuine 24p frame rate. Before this model, all previous HD camcorders by Canon (and most other makers) offered 60i (60 interlaced fields). The 60i framerate works like this: your camcorder snaps 60 full images per second. It then discards every other horizontal line from them, beginning with the first line for the first image, second line for the second image, first again for the third image, and so on, alternating lines. It encodes these half-images in consecutive "fields", each containing only even numbered lines, followed by one with odd-numbered lines. When you play this 60i material back, it shows these alternating lines, with black lines between them, 60 times per minute. The human eye blends them together into a smooth and (relatively) crisp motion. The significance of 60i is that this system is used in analogue standard-definition TV, and had been the foundation of video practically forever. The NTSC standard is defined on 60i (PAL system in EU uses 50i, and the images are also interlaced). The switch to HD allowed progressive-scan video, where a whole image is shown at the same time (no interlacing), much like traditional film. There are no different standards in HD (such as NTSC, PAL, SECAM, etc). HD is HD everywhere in the world. Well, unfortunately, due to the legacy of those old TV systems, HD in US is still most often shot at 60i (or 30p), and in EU at 50i (25p). To add more to this mess, we have the usual film frame rate of 24p.

Going back to your camcorder. Before your model, Canon used to offer (and still offers on other models) 24p, 30p and 60i. However, all these frame rates are encoded inside a 60i stream. For 30p, this is simple; each of those 30 progressive frames is broken apart into two fields; one containing only odd horizontal lines (with black space between them), the other containing even ones. These two fields are then encoded into a 60i stream. When this 60i stream is played back, it looks clear and smooth. If we take this 60i file and de-interlace it, the deinterlacer will simply fuze neighbouring fields back together into proper progressive images.

With 24p, situation is a bit more complicated. In order to spread 24 progressive frames into 60 interlaced fields, a process called 'telecine' is used. The 24p footage is again broken up into two fields (odd and even lines), and is re-inserted into 60i by following the pattern 2-3-2-3-2-3 etc. Here is a representation of how it looks. Let's say that individual progressive frames are A B C D E F etc. When they are broken up, they become individual fields A1 A2 B1 B2 C1 C2 D1 D2, etc. The resulting 60i stream also contains individual fields. The 2-3 interlacing goes like this:

A1 A2 B1 B2 B1 C2 C1 D2 D1 D2 E1 E2 F1 F2 F1 G2 etc.

In other words, it goes AA BBB CC DDD EE FFF, but uses odd or even halves of each progressive frame in alternating succession. When this stream is played back, it will be the smoothest approximation of 24p within a 60i stream.

The problem with this is, if we use some de-interlacer, without regard to this 2:3 telecine break-up, it will just fuse two neighbouring fields into a single frame. This will look bad, because every few frames, we'll get two fields that are NOT from the same original progressive image (in example above, B1 C2, then C1 D2, then F1 G2, etc). This is why smart deinterlacer must be used, which will analyse this 60i stream, detect which fields are from the same frame and fuse them together, discarding duplicate fields.

So, why does Canon (and others) do this 2:3 telecine song-and-dance? The only reason seems to be so that you could connect that camcorder to your old-fashioned, analogue Standard-Def TV (via that analogue composite yellow-white-red RCA connector) and play it back correctly. HDTVs don't need 60i stream; they can display 24p, 30p, 60p and any other frame rate perfectly fine.

Now, what does this all mean for you? Well, if you are making videos for YouTube, you definitely want to upload a truly progressive frame rate (with 24 or 30 pure, uninterlaced, non-telecined frames), since they don't do interlaced. Therefore, your best bet for YouTube will be to shoot the true 24p framerate (and not the other one, encoded inside 60i stream). I have also uploaded videos shot in 30p but encoded as 60i, and YouTube deinterlaced them correctly, without any artifacts. However, 24p in 60i was deinterlaced poorly, which tells me that YouTube's deinterlacer doesn't recognise telecine (2:3 cadence). For DVDs, Blu-Ray discs, AVCHD discs an YouTube, it is best to use 24p or 30p. The only time you may want to shoot, edit and deliver in 60i is when you are shooting fast action (sports, racing, etc), and want to get fastest possible motion. And even then, you'd only do it if you're planning to deliver that video on standard DVD or Blu-ray (or AVCHD disc). YouTube will deinterlace that true 60i video, and it will look blurry played back in 30p.

I hope this helps.

[Daniel Webb]

when sony vegas makes me save my avchd edits that were shot in 24p to 29.970 am I losing any quality or will there be any negative effect on the footage? For some reason if I insist on keeping the format as avchd then it insists that the footage either be 25fps or 29.970

[Predrag Vasic]

If that original 24p footage was a pure 24p (i.e. without any duplicate fields), and the Vegas project timeline was also 24p, then Vegas should definitely allow you to export your project as 24p AVCHD. If it doesn't let you do that, this is telling me that your 24p footage was the other 24p type, that encodes inside 60i, and was actually brought into Vegas in its 60i interlaced form, with those duplicate "pull-down" fields, and Vegas is treating it as if it were ordinary 60i material. If this material is then edited on a 60i (or worse, 30p, or 29.97) timeline, Vegas simply won't know that the original frames were captured at 24p and then chopped up, interlaced and pull-down inserted to fit into 60i. Instead, Vegas will just combine neighbouring pairs of fields to make up 30p (or 29.97). Without properly removing duplicate fields, this would result in really, really bad video, especially where there is motion, because almost ever other frame will contain two halves (two fields) that were originally parts of different frames.

Editing 24p captured inside 60i stream is a bit of a pain if you don't have tools that will let you remove that pulldown from the 60i stream and convert that original footage into true, pure, actual 24p. Since your HF-S200 has that other, pure 24p mode, if you like the 24p framerate, you should shoot in that mode and edit in Vegas on a 24p timeline.

[Daniel Webb]

the cam I have has two different 24p modes: pf24 and f24. From what I understand the pf24 encodes inside 60i or whatnot and the f24 is a new feature just released this year that allows for recording in true 24p

[Richard Grebby]

24f seems very jerky when recording in camera, is this usual?