720/60p with 1/30 for 30p

Ben_B

Ben_B

Veteran
I had a quick question. I remember that there had been talk about using 720/60p at 1/30th of a second...this will result in doubled frames and basically 30p in a 60p stream. I am shooting some students talking about themselves in a classroom setting and have to make DVDs for each one of them of each of them. Because this is for DVD, and because I want to save time by avoiding pulldown removal, I am thinking of shooting using 720/60p...but I want the 30p look. I am confident I can manage my lighting conditions properly at 1/30th of a second and am not worried about motion blur, I have used it before at 24p and like it. Also, I like that shooting 30p in AVCHD will save me some space on the card so I will have to change them less (vs 60p AVCHD [because the 1/30th will actually save space due to the compression, anyone who has ever shot slow shutter on the GH1 knows the thing will roll FOREVER, in this case, twice as long] and of course vs motion jpeg)

Anyway, getting to the point: does anyone see any problems with editing frame-doubled 60p in a 60p timeline for a 30p look AND burning it to DVD, without doing any modifications to the footage other than normal conversion to an I-frame codec. Barry? Thanks!
 
Barry_Green said:
Why not just use the MJPG mode? It's already 720/30p...
Click to expand...

Because it only holds like 8 minutes on my 4Gb cards, less with the hack. In theory the 720/60p mode at 1/30th will do 50 (post firmware hack.) 720/60 at other shutter speeds will do 24.

I will shoot some tests tomorrow, I think I can probably get the stuff to be 30p in post anyway, whether I shoot 1/30th or not...I could just drop it in a 30p timeline! Yes?
 
I suppose this will come down to what your tests give you, but I do remember that discussions about dropping the shutter created some weird framerates within the stream, like 20p!?

This might have been PAL cameras shooting at 1/30 and lower, but I can't be sure.
 
In my tests at 1/60 and 1/125 I managed to get a card speed error with some crazy motion, which shouldn't be a problem for this, but I'd prefer to shoot 1/30th if this works out even though I think any can be converted to 30p, just because I don't want to risk the error popping up. Can't get it to pop at all in 1080/24p. C settings, Class 4 San Disk Ultra II cards.
 
Ok tests completed:

720/60p with 1/30 indeed creates a 30p look in a 60p timeline with doubled frames. It also has lots of motion blur, but of course gets you a stop more light. If dropped into a 30p timeline every other frame gets dropped and it is normal 30p. I cannot get a card speed write error with these settings, likely because it's actually encoding half the data of 60p. Similarly this will give me the maximum recording time on the card.

720/60p at 1/60th is normal smooth 60p. If dropped into a 30p timeline every other frame gets dropped and it looks like normal native 30p with a 1/60th shutter....so nice, in fact better than the 1/30th of a second for things with lots of motion as it has less crazy motion blur. However, it is a stop slower than 1/30th of a second, and I managed to get card speed write error with it if I moved the camera around a ton on a wide, stopped down lens, in a high detail environment. Likely not a concern with the shoot I will be doing, but still a risk with the cards I am using in an environment where I can't just do another take. It also will give me half the recording time on the card of 1/30th.

Conclusion:
I think I will end up shooting at 1/30th of a second. It will give me more light which is good when shooting indoors with the kit lens. It will give me twice the capacity on my card. I don't have much motion so the blur shouldn't be distracting. There is no risk of card speed error.
 
for what it's worth, i've been shooting native 24p with the C hack settings to sandisk ultra II class 4 sdhc cards without a single write error. doesn't make any sense, but...
 
bewillia said:
for what it's worth, i've been shooting native 24p with the C hack settings to sandisk ultra II class 4 sdhc cards without a single write error. doesn't make any sense, but...
Click to expand...

Oh I have been as well, 1080/24p is about the same amount of data per second as 720/60p, but since 60p has more frames it might have something to do with the way the buffer is set up...it has only happened in 60p with me, and it doesn't happen at 1/30th (cause it's encoding less.)
 
Ben, you can also drop AVCHD framerate to 29.97 fps by using AVCHD FPS patch under "Patches for end users". This should further reduce card space consumption by not creating duplicate frames.
 
svecher said:
Ben, you can also drop AVCHD framerate to 29.97 fps by using AVCHD FPS patch under "Patches for end users". This should further reduce card space consumption by not creating duplicate frames.
Click to expand...

The duplicate frames shouldn't take up much space on the card assuming they're P frames, which they are, no way I'm gonna get too I frames in a row with this GOP...but it would save me some space when I transcode, but that's sort of a non issue. Thanks though, I like having flexibility away from the computer to do 60 or 30. In any case, I managed to shoot the whole first day on one 4gb card, around 50 minutes of shooting or so (on a plain whiteboard background.)
 
You must log in or register to reply here.
Back
Top