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Why would I want to use 24p mode on my camera?

Today, many video cameras provide a “24p” mode for recording video at 24 frames per second.

The default or normal mode of most video cameras is “60i” which is 60 half frames per second. Many cameras also now feature a “30p” mode or 30 frames per second.

Why all these choices?

See below – 60i is an old technology that we still use for historical reasons.

If you are making your video for online distribution, you definitely want to choose 30p or 24p mode. These record in “progressive” (like a digital still camera rather than the funky interlaced 60i mode) which is also compatible with computer displays.

Consequently, if you want to output to the web or to a computer, you will want to use 30p or 24p “progressive” modes to avoid the “interlace jagged edges” of 60i. (It is possible to de-interlace video too – but that is for another day.)

So why 24p?

Some people like that it looks like 24 fps film. I like it for a much different reason: better low light performance and better compressibility for the online world.

When you shoot at 60i, you’ll typically use a shutter speed of 1/60th of a second. When you shoot at 30p, you’ll likely use either 1/60th or 1/30th of a second.

At 24p, you’ll likely use either 1/48th or 1/24th of a second.

1/24th of a second lets in 20% more light than 1/30th of a second and more than twice as much light as 1/60th of a second.

Consequently, 24p has some what better low light performance – that is, the camera will add less video amplification, which adds a bit of noise or graininess to the images. Shooting in 24p means cleaner, less grainy images – compared to higher shutter speeds.

Another advantage is editing and compressing for the web.  A video clip recorded at 24p has 20% fewer frames than one recorded at 30p – so it takes less time. And there are situations where I’ve recorded a live event that I turn around and post online as fast as possible.

Another issue is compression. For a given video streaming data rate, say 1 Mbps, 24 fps will will compress a bit better than 30 fps. But do realize it is not a straight forward “definitely better” as MPEG4 compression depends heavily on the nature of the content of the frame.

Editing 24p

Unfortunately, this may require an advanced or professional editing package. I can’t help you there very much, but I did write some info about doing this on a Mac. (I also do some editing on Windows but have not tried this there.) Some additional information is also here.

Cameras, Techniques

Recording direct to disk from a Firewire equipped camcorder

There are mini-disk products that you can connect directly to your Firewire equipped camcorder to record direct to disk. But then tend to range in price from about $600 to $1800 depending on used vs new, capacity and vendor.

An alternative is to record direct to your notebook computer.

If you have a Macbook or Macbook Pro, a very easy way to record direct to disk is to connect the Firewire output of your camcorder to the notebook computer and then run iMovie and import from the camera.

The camera should be in its “camera” mode but does not need to be recording to tape. Whatever the camera sees will be recorded direct to disk.

This works with my Canon HV30 in HD mode and I’ve done it using both iMovie 8 and the older iMovie HD (version 6) connected to a Macbook.

On Windows, there are several software utilities available that will enable you to do the same thing. While I am typing this on a Windows desktop, I do not have a Windows notebook on which to test this out!

The main advantage to doing this is to overcome the occasional tape dropout problem that tends to plague HDV format.By recording direct to your notebook computer disk, who cares about tape dropouts! (Caution – you may want to use a longer Firewire cable to keep the notebook away from your camera mic, especially if the fan kicks on to keep the CPU cool. Not all cameras have sufficient drive signal to use a longer cable, though. So be sure to test out your configuration first!)

On SD recordings, a video dropout typically lost a single 1/30th of a second frame. If you even noticed, you could always copy an adjacent frame and no one would notice.

With HDV you can lose up to 1/2 second per dropout – and I guarantee, everyone will notice!

Two other steps to avoiding dropouts are to clean your video heads in the camera every 5 to 10 hours of recording – I use a Canon cleaning tape for about 10 seconds but I’m told most any cleaning tape is fine. The other important step is tape quality – I used to use TDK tape all the time on my SD camera with excellent results – but the SD tapes always had dropouts when recording HDV on standard TDK tape.

I switched to Panasonic AMQ (HDVM63AMQ) tapes and have now recorded probably 75 hours with excellent results on that tape. I buy mine from TapeStockOnline.com. They have consistently quick order fulfillment and decent prices. If you are used to buying standard miniDV tapes at the local discount store  you’ll find that high quality tapes for HDV are more expensive – currently $5.25 in a minimum order of 10 units.

There are other brands that cost both more or less than these but I’m sticking with what has worked well for me. Hopefully this note provides some idea for you to try if you are plagued by video dropouts!

Editing, Techniques

Why does my 30p video show up as 60i?

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I’ve seen some confusion on the online forums regarding shooting in 30p (or 24p) and then importing into a video editor.

Why does my 30p video show up as 60i in <name your editor>?

In an interleaved 60i video (normal old fashioned video), the image is scanned 60 times per second, producing one half frame at each scan (say the odd scan lines, followed by the even scan lines in the next half frame). Because movement can occur between the two half frames, you some times see interlaced jagged edges.

A better way is to take 30 still pictures per second of the entire image.

When your camera records at 30p video, it takes a single image – but splits it into two half frames and stuffs those into two 60i half frames (without any jaggies since its splitting one image in to two pieces whereas 60i creates one image from two separate pieces taken 1/60th of a second apart).

Consequently, a 30p video is stored as a 60i video. And two consecutive half frames, put together, become 30p. Your video software can’t tell the difference between between 60i and 30p.

So why do we have these strange 60i half frames? Historic reasons. The earliest TVs were not able to scan the full image top to bottom before the next image would arrive. The solution then was to draw only half the lines in each interval. Thanks to the persistence of the phosphor image of old TVs, the first lines remained glowing while the TV then scanned the alternate lines.

No one would design a TV like that today – but we’ve lived with it for many decades and it is still supported for compatibility reasons.

I can import 24p video into iMovie (or other editor) but it plays weird – why?

This depends on the camera. But it is common to store the 24p image in half frames, similar to 30p. But since 24 does not evenly divide into 60, the sequence of half frames is a little different.

In 30p, the sequence is basically 2:2:2:2:2:2 and so on where the 2 signifies 2 half frames.

In 24p, the video may be stored in various combinations such as:

2:3:3:2 or 2:3:2:3

In this way, the 24p mode uses up more half frames – consider 2 half frames and then 3 half frames. This slows down the video frames to match the 60i storage of the tape. Consequently, 24p gets mapped into a funky sequence of half frames on the 60i tape.

To a program like iMovie, this 24p footage looks just like 60i. But unfortunately, iMovie (And many other video editors) have no way of knowing that it is not really 60i footage with some frames appearing 3 times. So play back and edits produce strange artifacts.

If you want to convert this to proper 24p footage and then edit in an editor that supports 24 frames per second see these instructions.

Online

Youtube adds 1080p capability

HD videos uploaded in 1920 x 1080/p will – probably – be transcoded by Youtube into 1080p videos. This represents an upgrade from Youtube’s 1280 x 720p maximum HD resolution.  (“Probably” because Youtube says not all videos will be converted just yet.)

The 1080p videos, however, are useless for most computer displays as few have 1920 x 1080 sized displays. The main advantage, probably, is that in a near future world, we will be watching streaming videos over the Internet – on our real HDTVs, arriving via a set top box.

Worse, you’ll need a very fast processor to watch the new 1080/p HD videos. I can’t watch them on a 3.2 Ghz Windows OS computer – and I can watch them on my quad core Mac Pro only if I wait for the video to download entirely, first. The problem is the video stutters badly as the processor cannot keep up with the Flash video decoding.

Recommendation: Upload the HD video but don’t select the HD option during play back.  It looks like the new “normal” is 1280 x 720 – so you don’t need to select HD.

Online

youtube Failed (upload aborted)

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uploading Failed upload aborted – YouTube Help.

Just an FYI – this is happening to me, also. It has been impossible to upload videos to YouTube the past couple of days. Actually, I can upload short videos, say 30 seconds long – YouTube gives an error but processes the video anyway. Longer videos, such as 5 minutes, always fail. I suspect this is due to YouTube’s new 1080p upgrade not working.

Nothing changed on my end – or for the many others experiencing this problem. Today is Saturday, November 21, 2009 for reference.

There is a work around, apparently: Use the multi-video or bulk video upload option. This does work for me and others.

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