720p doesn't make sense

B

blockrocker

Member
Hi!

The 720p recording option doesn't make any sense to me. Maybe someone can explain what I'm missing!

From what I understand by reading these forums, when you record 720p the bitrate is as high as with 1080p and that's because each frame gets recorded twice.

But what sense does it make to save duplicate frames? Why would anyone ever want to have each frame saved twice when it just doubles the filesize?
 
OK, bear with me here...

720pN30 records 30 unique frames per second
720p30 records 30 duplicated frames per second (for a total of 60 frames)
720p60 records 60 unique frames per second

1080p30 records 30 duplicated interlaced frames per second (giving the illusion of 30 full frames)
1080i60 records 60 interlaced frames per second

The bitrate is the same because in both 720p60 and 1080i60, a nearly identical amount of information is recorded for each frame (the full frame at 720 or interlaced frame at 1080)

The HVX does not record 1080p60

So, 720p60 makes sense for recording full-speed with an option of smooth, non-jaggy slow-motion in post, particularly for sports and so forth.
 
mcbob said:
OK, bear with me here...

720pN30 records 30 unique frames per second
720p30 records 30 duplicated frames per second (for a total of 60 frames)
720p60 records 60 unique frames per second
Click to expand...

Thanks for helping out!

Just to make sure if I understand correctly:
"720pN30 records 30 unique frames per second" So these are 30 progressive frames right?

"720p30 records 30 duplicated frames per second" Are these then interlaced frames? Or why else are you talking about a total of 60 frames? If they are interlaced, then why does it say 720p30 and not 720i60?

mcbob said:
So, 720p60 makes sense for recording full-speed with an option of smooth, non-jaggy slow-motion in post, particularly for sports and so forth.
Click to expand...

This confuses me: It says 720p30 in the camera menu, not 720p60. Why are you referring to 720p60 here?
 
I didn't know to which form of 720p you were initially referring, so I gave info for all of them.

Yes, 720pN30 records 30 progressive frames per second.
720p30 records duplicate progressive frames in a 720p60 stream.
720p is never interlaced (whether 30p, 60p, or any other flavor)

In this case, the reason a fellow would reasonably use 720p30 over 720pN30 is if they wanted to output a live feed via firewire, which is not possible with the pN framerates (as they don't reside in a TV-friendly 720p60 stream). If recording to P2 only, then 720pN30 is the most sensible option.
 
The 30p and 24p 720 recording modes (not the N modes) record in an "over-60" stream because that's the actual DVCPRO HD recording standard. It (59.94) is also the broadcast standard, so any 720/24p material you see on HDTV will be embedded in a 59.94 stream.

(This is in 60hz/NTSC territory, of course. 50hz/PAL is another story.)
 
Some prefer 720p over 60i. IN fact some networks demand 720p content.
Correction:1080i60 records 60 interlaced frames per second

That is records 60 FIELDS a second.

Under and Over cranking are only available in 720p mode.
 
It also offers longer record times per gig of memory. Even more so if you shoot in native. For long form recording, this can make your life easier.

Grant
 
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