Data Rate of 'slow mo' with EX

[GuyB]

Perhaps someone can help me get this right. On other forums I have seen people claim that when recording for slo mo (aka over cranking) on the EX1 the data rate is higher than 35Mbps.

Now as far as I understand our EX1s can't really overcrank 1080 as they can't exceed 30fps recording. They only way to get some form of overcranking is if you choose to capture at say 30p and edit to a slower frame rate format such as 24p or 25p (which may be technically overcranking but it is very limited), or if you accept working in 720 when you can record up to 60p but of course at lower resolution (is there much difference in recording 720 60p or doing a 50% slow mo on 1080 60i?) But its not like we are capturing up to 120fps. This stuff certainly isn't why I bought my EX1.

Ok, so back to the start, excluding SP, all of the recording formats on the EX1 are 35Mbps arn't they? There isn't any burst frame frate recording etc No slo mo setting which records at higher data rate for some reason.

Cheers

Guy

[Barry_Green]

I'm pretty sure I tested this, and the EX1, when using S&Q mode in 720/24P and setting the frame rate to 60fps, will actually create a data stream about 90mbps.

If you put it in 720/60P it'll be 35mbps, but if you use 24P @ 60fps it'll instead take up 90mbps.

I'm sure some EX1 owners will be along to verify or correct this, but I think I remember it properly.

[GuyB]

OK, so perhaps what it is doing is taking each 24 frames and recording them in 35Mbp so each 60 frames arn't recorded in 35Mbits (as it would normally be in 720 60p), but (60/24)*35 Mb.

That would increase the data rate yet maintain the same data compression when playing back in slo mo.

Anyone else able to add some insight to this?

Cheers

Guy

[matthew77]

You are both correct. When overcranked or undercranked, the camera maintains its data rate per second of screen time, rather than record time.

So 24p screen time overcranked to 60p will record at 35Mbps x 2.5 or 87.5 Mbps (give or take).

When over undercranking it's also worth noting that the time code maintains a base of the preset screen frame rate (24p for example) and the timecode moves faster or slower depending on the over/undercrank setting.

[RDykmans]

Is there a way (in FCP) to get overcranked footage to play at normal speed without the software doing the frame interpolation? In other words convert 24p/60 or 30p/60 to 60p? I tried dropping it on a 60p timeline and telling FCP not to change the seq settings but it's still playing back in slomo.

[basspig]

matthew77 is correct about the data rate.
Since 720p/60 is recorded at 35mb/s the data rate per frame is lower than if you use S&Q recording at 60/24. I believe that I am seeing a slight perceptable difference in quality between 720p 30 and 720p 60, but I need to set up a scientific test to achieve certainty.

I made the realization that the data rate was higher in overcrank at the fireworks, when I ran out of 16GB SxS space on a 20-minute fireworks display. That got me curious enough to analyze what was happening during recording.

Now we see another reason for the performance of SxS media--it actually gets written to a lot faster than 35mb/s sometimes. And anyway, that's said to be an average data rate. Who knows.. the peak could be almost double that with fast moving images.

[GuyB]

It also makes sense that the new 60GB HDD can't support slo mo as well as it can't handle the sustained higher data rates like SxS can.

[basspig]

Plus there's no output from FireWire during S&Q mode.

[janusz]

apart from the data rate, is the EX's over/undercrank footage comparable in look to the HVX's very effective variable frame rate footage?

[matthew77]

It's as good or better.