OK, in light of Sony confirming no loss of quality in 50P, I've been thinking about shooting in it all the time. But here are some of my thoughts over a workflow that I'd welcome feedback on.

When editing in Premiere CC and using a FS5 XAVC HD 50P clip to automatically create a sequence, Premiere always generates a 'AVCHD 1080P square pixel' sequence with (unsurprisingly) 50 frames per second. If I do the same with 25P footage Premiere generates a 'Arri Cinema' sequence with 25 frames per second. After doing various tests relating to render and export times the bottom line is 50P is more CPU intensive than 25P, by about (again no surprise) 50%. Initially I wondered if the type of sequence (i.e. AVCHD vs Arri) had any bearing on results re the sequence codecs, but I don't think it does since you can go into the sequence settings and turn an Arri 25fps sequence into a 50fps and all of my test results will then pretty much match their AVCHD equivalents.

So my conclusion here is 50P requires approx. twice as much CPU time as 25P regardless of the sequence codec (at least between Premiere's auto choices for XAVC HD).

So then I started to wonder if Premiere can retain access to all of the 50P frames on a 25P sequence in much the same way you can scale up a 4K clip (and use the resolution above 1080) on a 1080 sequence in Premiere? Alternatively does it throw away every other frame on a 25P sequence and you can't get it back without generating a 50P sequence?

If the former is true you would be able to edit most of your 50P footage on a 25P sequence (avoiding heavy CPU usage) and then for those odd clips where you want to slomo them (to 50%) Premiere would still have access to all 50 frames of the 'original' clip and thus can stretch them on your 25P sequence producing smooth 50% playback.

Unfortunately my edit PC is away for repair and so I can't test this until it comes back. But maybe someone else can?

If the former is true you would be able to edit most of your 50P footage on a 25P sequence (avoiding heavy CPU usage) and then for those odd clips where you want to slomo them (to 50%) Premiere would still have access to all 50 frames of the 'original' clip and thus can stretch them on your 25P sequence producing smooth 50% playback.

I always edit 50p footage in a 25p timeline in Edius and slowing down the footage 50% gives smooth motion, this should also apply for Premiere.

This is how Sony responded:

"That way of explaining would be correct in an Intra codec. However, since you record in XAVC Long GOP, there is no such "double quality" in a 25p frame compared to a 50p frame"


OK, in light of Sony confirming no loss of quality in 50P, I've been thinking about shooting in it all the time.

This may just be semantics, but I'm not sure that the Sony statement says 'No Quality Loss' -- I would interpret it to mean 'minimal quality loss for most shots.'

I think the 'double quality' reference really goes back to arguments about the original Panasonic Varicam 100mbps recording system (which here in the States recorded at 60 fps intra) -- where you were essentially throwing away 50% of your frames at 30p, or 60% of your frames at 24p -- and thus your effective usable compression at 24p was actually 40mbps, not 100mbps.

I'd be careful about inferring that you aren't losing any quality at 50p or 60p -- since as mentioned elsewhere in the thread Long-GOP is most efficient when there is minimal change between frames, but the flip side of this statement is that when there is significant change between frames the Long-GOP is not as efficient.

As a side note -- one of my clients has a bunch of XDcam disc cameras which they have standardized for many years at 25mbps (SP) compression. (It's a well known syndicated tv show that airs both in the US and internationally, and they generate more than 250 hours of programs a year). For them the quality difference between the 25mbps Long-GOP and higher bit rates was considered minimal when compared to their savings in discs and data storage. That was their decision, based on their needs and perceptions. Meanwhile, for any of my other clients, 35mbps (XDcam 4:2:0 HQ) would be the absolute minimum data rate they would accept, with many requiring 4:2:2.

So -- I'd still recommend doing your own tests to determine whether the higher frame rate is better for you -- based on what you'll be shooting and where it's being seen... I just can't construe the Sony statement as meaning 'Absolutely no potential quality loss' at the lower effective bit rate.

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I'd be careful about inferring that you aren't losing any quality at 50p or 60p -- since as mentioned elsewhere in the thread Long-GOP is most efficient when there is minimal change between frames, but the flip side of this statement is that when there is significant change between frames the Long-GOP is not as efficient.

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FS5 is all LongGOP so there are less incremental data needs when recording 60P than at 30P. But there are twice as many data points. At 100Mbps I doubt there is much difference but suspect that 60P is still less and consequently a better choice. This is just an argument for LongGOP it definitely does not apply for iFrame codecs where there is twice the difference. If you follow your argument it is 30P that will have the quality loss ?

Ron Evans

FS5 is all LongGOP so there are less incremental data needs when recording 60P than at 30P. But there are twice as many data points. At 100Mbps I doubt there is much difference but suspect that 60P is still less and consequently a better choice. This is just an argument for LongGOP it definitely does not apply for iFrame codecs where there is twice the difference. If you follow your argument it is 30P that will have the quality loss ?
Ron Evans

I'm going on the assumption that the length (in frames) of each long-gop sequence will be the same no matter what the frame rate -- hence when shooting at 60p you will be recording twice as many 'GOPs' as at 30p in the same length of time. But recording bit rates will be based not on number of frames but on time. My guess is that the codec would be pushed harder when shooting motion-intensive subjects with plenty of change every frame, no matter what the frame rate (sports action, waves breaking, sparklers, corn flakes pouring, pans of large groups doing calisthenics, etc) at 60p than at 30p if recording at the same bit rate -- since there would be significant changes in every frame, and you are still utilizing less data per GOP sequence at 60p than at 30p, since you have twice as many GOP sequences. So no... I would expect the 30p to look marginally better, depending on subject...

Thus my suggestion to test with the type of footage you will be shooting.

I guess my point is that at the rates we are taking about the motion changes at 60P is a lot less than at 30P so although there will be more of them each change is a lot less load on the encoder than the changes at 30P for the fast action you mention where there will be also judder involved in any camera movement at 30P. If you were talking about lower data rates there may be a difference but at 50Mbps I doubt anyone will see a difference. Clearly there is a data rate at which the encoder just cannot manage to encode. However we are talking about 50Mbps not the lower limit. The data rate differences at AVCHD for 30P and 60p may give some indication of these lower limits. 24Mbps for 30P( or 60i same sampling rate as 60P but half frames ) and 28Mbps for 60P. So to make up the full frames( 60i to 60P ) requires another 4Mbps for AVCHD. Both 24Mbps and 28Mbps are max levels too not the average. XAVC-S is more efficient and at 50Mbps.

Ron Evans

I export my videos in 25p as well to vimeo and the noise you see in my videos on vimeo are there in the native files, it's because I"m not shooting with a c100 or a7sII. :)



I shoot at 50fps at 1/50 shutter so the same amount of light comes in but with extra benefits, there is no light loss in this case and again, show me one shot in above video where shooting at 50fps and 1/50shutter would somehow be worse then 25fps and 1/50shutter because there are plenty of shots like that.




I never change framerates on the same camera at a wedding unless I absolutely have to, it only makes my job more difficult for no reason or benefit. If I would forget to change the framerate I might regret it later on if I want to slow footage down and it was shot at 25fps.

so shooting 25P 1/50 or 50P 1/50 has the same amount of light hitting the sensor?

Yes of course. The shutter is staying open for 1/50 of a second for each time the camera records a frame. It is how long the shutter is open governs how much light falls on the sensor not how often. Just with 50P you have the option to use it at 50P for smooth motion or on a 25P time line for slower frame rate motion.

I thought (wrong) that 25P or 50P also affected the light fall on the sensor. Thx for the answer Ron!