30p or 60i?

enespacio wrote on 1/19/2010, 7:18 AM
The manual for my Canon HFS100 states the following, "capture video in 30p (30 progressive frames, recorded to 60i). That statement alone is confusing. I generally film at the 30p setting, When I use vegas "Match Media Settings" in project properties, it picks: HD 1080-60i (1920x1080, 29.970 fps) and Upper field first.

So should I keep these settings as is, or change the field order to progressive? I mostly render out to .mp4 for use on Vimeo.

Comments

Jay Gladwell wrote on 1/19/2010, 7:21 AM

For online video, you should use progressive.

musicvid10 wrote on 1/19/2010, 7:28 AM
See what MediaInfo reports. Vegas occasionally guesses wrong, but your render settings determine the output.
farss wrote on 1/19/2010, 7:30 AM
Change the media properties to Progressive, do the same for your project settings.
The problem seems to arise because there's no way to flag some media types as progressive, only upper or lower field first.

Bob.
enespacio wrote on 1/19/2010, 8:59 AM
I downloaded and ran MediaInfo on a typical video that I filmed at 30p and got these results. This seems to be the same as what vegas recognized, Either Bob is right and this media isn't being flagged as progressive, or the HFS100 is outputting 30p as 60i.

ID : 0
Complete name : E:\Mts files\TKD\forms website\00028.MTS
Format : BDAV
Format/Info : Blu-ray Video
File size : 124 MiB
Duration : 44s 10ms
Overall bit rate : 23.6 Mbps
Maximum Overall bit rate : 24.0 Mbps

Video
ID : 4113 (0x1011)
Menu ID : 1 (0x1)
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.0
Format settings, CABAC : Yes
Format settings, ReFrames : 2 frames
Duration : 43s 910ms
Bit rate : 22.4 Mbps
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate : 29.970 fps
Resolution : 8 bits
Colorimetry : 4:2:0
Scan type : Interlaced
Scan order : Top Field First
Bits/(Pixel*Frame) : 0.360
Stream size : 117 MiB (95%)

Audio
ID : 4352 (0x1100)
Menu ID : 1 (0x1)
Format : AC-3
Format/Info : Audio Coding 3
Duration : 44s 32ms
Bit rate mode : Constant
Bit rate : 256 Kbps
Channel(s) : 2 channels
Channel positions : L R
Sampling rate : 48.0 KHz
Video delay : -66ms
Stream size : 1.34 MiB (1%)
musicvid10 wrote on 1/19/2010, 9:03 AM
I'm betting your software captured 30p but didn't change the flags. Following Bob's advice seems the most logical starting point.
TheHappyFriar wrote on 1/19/2010, 9:42 AM
easiest way to tell is to get a horizontal motion scene, preview good/full & see if you get interlace lines.
Andy_L wrote on 1/19/2010, 12:10 PM
My understanding is that the Vixias are not recording progressively. The 30p setting is a software setting for outputing a "progressive" signal to your TV. Everything is recorded as 60i. Some have suggested that the sensor is recording a progressive frame, but that specialized software/techniques are required to rebuild it from the 60i file.
enespacio wrote on 1/19/2010, 12:35 PM
Andy, it appears that you are correct. I just found this statement in a review of my camera.

"There's one caveat though, and that's the fact that the Vixia HF S100 does not truly record native 24 and 30 frames per second video because those modes are purely fancy simulated filters. Furthermore, the Vixia HF S100's 60i mode means that frames are interlaced. What's happening here is that the camcorder is recording 30 frames of horizontal lines in one configuration and 30 frames of horizontal lines in a secondary configuration. This happens every other frame so when played back, the frames appear to blend together."

Now I wonder whether or not I should start filming in 60i instead. I shoot a lot of martial arts videos, where the pace is very fast.

James
Laurence wrote on 1/19/2010, 12:52 PM
I usually shoot 30p, but still choose 60i for fast motion like sports. For a martial arts video I would choose 60i. Not only will the motion look better, but you'll be able to do good looking slow motion.
John_Cline wrote on 1/19/2010, 12:57 PM
If you're shooting fast motion, 60i has twice the temporal resolution of 30p. For that matter, you can easily generate a real 960x540 60p video from 60i HDV or AVCHD without any tricks or interpolation.
farss wrote on 1/19/2010, 1:19 PM
You need to understand the difference between what the camera shoots and what it records.

Many cameras shoot 30p but record it as 60i. Technically what they're recording is 30PsF60 i.e. 30 Progressive (frames) Segmented (into) Fields 60 (per second).

When you combine them back into frames there will be no interlace artifacts and as noted previously this is easily checked. 30PsF60 does not have the temporal resolution of 60i.

Many reviewers state that 30PsF60 is not "true" progressive and they are WRONG. If a camera is shooting 30p then it takes 30 pictures per second. If it's shooting 60i then it has to take 60 pictures per second. They might only scan every even or odd line, that's the traditional way it's done or they could still scan the whole sensor and discard every second line. I wouldn't be surprised if many of the cameras that do shoot progressive do this. Either way it doesn't matter.

Bob.
enespacio wrote on 1/19/2010, 2:03 PM
Bob, I was beginning to think that the 30p setting in my camera might just be a gimmick, but now I fully understand the concept. I should confess that I did have to read your explanation 3 times before it sank in. You should submit that explanation to wikipedia.

Do you also agree with some of the other's here that prefer shooting 60i for fast motion? If I'm reading your explanation properly, you are agreeing with John that 60i has better temporal resolution.
John_Cline wrote on 1/19/2010, 3:47 PM
There is no agreeing necessary, 60i has twice the temporal resolution of 30p. This is an absolute fact. 60i has 59.94 individual images per second, 30p has 29.97.
enespacio wrote on 1/19/2010, 9:06 PM
John, Thanks for the clarification. Additionally, I would really like to know what project settings I should use to generate a real 60p video from my 60i AVCHD? Do you lower the resolution to 960x540 in the project settings, or not until rendering?
James
Laurence wrote on 1/20/2010, 7:42 AM
Quite often 30p is flagged as 60i. That is because 30p played back as 60i looks the same as 30p played back as 30p. If you buy a DVD of the show "Friends" for instance, the footage is 30p (shot on film by the way), but the DVD player will be told to play it back in 60i mode. Looks the same either way so it doesn't matter.

That isn't to say that there isn't a difference between 30p and 60i however. In 30p all the lines in a frame were captured at once every 30th of a second. In 60i, even and odd fields are captured alternately every sixtieth of a second.

On most HDV cameras, the actual sensors are 960x540 and the three RGB color sensors are offset a little to give you a resolution across of 1440 instead of 960. The up and down resolution is still only 540. Putting such a camera in progressive mode really doesn't get you any more vertical resolution. You still only have the 540 lines of the sensor. On such a camera (a Z1 for instance), shooting 30p is sort of pointless.

The HVR Z7 uses three 960x1080 pixel sensors which are offset in such a way as to give 1440x1080 in the 34p and 30p modes. In this case 30p does give you a higher resolution image and is worth using.

30 frames per second is not anywhere near fast enough for fast motion though. For sports I still like the 60i mode.

Because the sensors in 60i HDV are functioning at 960x540, it is possible to extract a very nice 960x540x30p with square pixels. That is a wonderful mode for Internet broadcast, and in fact the format the iMovie is pushing right now. You loose the temporal resolution, but if you are starting with 60i HDV, you can render out a really good looking 960x540x30p with great looking slow motion in places that kicks butt for sports footage.
Laurence wrote on 1/20/2010, 8:02 AM
Just one last thing:

The highest resolution you can get on a Vimeo Pro account without paying for the plays is 855x480x30p. This looks wonderful (like a DVD), doesn't require a huge amount of bandwidth or a fast playback computer, and renders very nicely from a 60i HDV project. It is my main delivery resolution these days.
Andy_L wrote on 1/20/2010, 10:24 AM
Bob,

Have you found a way to import the 60i stream from a Vixia camera and convert it to 30p in Vegas to confirm the sensor was actually recording a progressive frame?

Even if the Vixias are recording a progressive frame split into separate fields, if there's no easy way to blend the fields back together, it's hard for me to call these progressive cameras.
TheHappyFriar wrote on 1/20/2010, 10:54 AM
There is no agreeing necessary, 60i has twice the temporal resolution of 30p. This is an absolute fact. 60i has 59.94 individual images per second, 30p has 29.97.
I did some quick math.
30p = 30 fps @ 720x480 (NTSC).
60i = 30fps @ 720x240 & another 30fps @ 720x240 (NTSC).

30p = 10,368,000 pixels displayed per second
60i = 5,184,000 + 5,184,000 = 10,368,000 pixels displayed per second.

So the resolution is exactly the same, just one has 2x as many frames @ 1/2 the resolution. :)

Useless data to me but useful to someone!
johnmeyer wrote on 1/20/2010, 11:37 AM
So the resolution is exactly the same, just one has 2x as many frames @ 1/2 the resolution. :)A slight clarification is necessary..

First, 60i and 30p have the same number of frames: nominally 30 frames per second.

Second, there is a difference between fields and frames, and it is what happens with the fields that defines the difference between 60i and 30p.

So, the correct way to describe the difference is that both 60i and 30p have the same number of frames AND the same number of fields. However, in 60i video each field (there are two interleaved fields in every frame) represents a different moment in time, whereas both fields in a 30p frame are taken at the exact same moment in time.

Thus, 60i has double the temporal information compared to 30p, and therefore looks more fluid and more "immediate." By contrast, 30p -- and 24p is even more so -- looks "removed" in time and "less real." This in no way says that one is better than the other, but merely that they impart a totally different feel to the video. When people say that interlaced video is horrible or that 24p, 25p, 30p, 50i, or 60i is somehow better or worse than some other cadence, that statement is just plain wrong. Each one is different but, as grade school teachers like to say, each is special in its own way.

And, just to be complete, in the original NTSC and PAL implementations of analog 60i and 50i video, every single line in each field represented a different moment in time, and in fact, each "point" along each scan line was taken at a different moment in time, so the temporal resolution, in some sense, actually approached infinity. The current "rolling shutter" implementations, to some degree, take us back in time to that way of capturing video.

farss wrote on 1/20/2010, 11:59 AM
"Even if the Vixias are recording a progressive frame split into separate fields, if there's no easy way to blend the fields back together, it's hard for me to call these progressive cameras."

If you're talking about 30PsF60 I cannot think of anything easier to do!

Change media properties to Field Order None (Progressive), put it onto a Progressive timeline, that's it, job done.

Bob.
Andy_L wrote on 1/20/2010, 12:55 PM
Amazing! I just confirmed an HF200 records a progressive frame on the P30 setting using your method. My opinion of this little camera has just skyrocketed. Thanks Bob!

Andy

**EDIT** I take it back. I just compared a more motion-intense video, and the Vixia's "progressive" scan is showing interlace artifacts--lots of them. :(
amendegw wrote on 1/20/2010, 1:37 PM
I'm confused. The OP wants to render mp4 to Vimeo (30p, I assume). Is he better off shooting in Canon's faux 30p or 60i? And what would one expect the difference to be in the rendered 30p mp4?

...Jerry

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Andy_L wrote on 1/20/2010, 5:18 PM
The difference is big. If you shoot 60i, you have to convert that into a 30p mp4 for YouTube/Vimeo, which means Vegas throws away one field per frame and interpolates that field into a whole (new) frame. You're not exactly losing one half your vertical resolution (1080 lines down to 540) because Bayer interpolation isn't that bad, but you are absolutely losing resolution in the process.

farss wrote on 1/20/2010, 6:07 PM
You can use Mike Crash's Smart De-Interlacer.
That way you have maximum temporal resolution for places where you can use it and still get progressive for the web.


Bob.