FS5 - R U shooting 25/30p or 50/60p?

[Nigel Davey]

I was wondering what folks are mostly shooting in on their FS5's and why? Being in PAL land thus far I've mostly been using XAVC HD 1080/50p 50mbps. But maybe I'm doing myself a diservice in terms of the extra processing needed in Premiere (compared to 25p) and the extra storage.

On a connected note, would it be worth transcoding into Prores before editing in Premiere to take the strain off of the CPU re XAVC-L? I tend to use quite a few filters/plugins for grading like Magic Bullet Looks, Neat Video, etc.

[Rajiv Attingal]

To my knowledge 25p and 50p records at the same bit rate. 50p increases temporal resolution i.e. smooth motion (no judder) in panning shots, as smooth as 50i. both records at same data rate (Mbps). Could be more compressed. So storage requirement is same.

[Dave Sperling]

Are you shooting for yourself or for clients? I pretty much try to shoot in whatever format my clients will be finishing to -- which means 90% of the time it's either 30p or 24p. If you think you may want to slow any of the footage down it's worth shooting at the higher frame rate to have the extra frames to work with.

In terms of the transcoding question -- your edit system/workflow is the deciding factor. If you find that the XAVC-L brings your system to its knees then by all means transcode. But if you are fine staying with the original camera format then my suggestion would be not to spend all that transcoding time. Remember, each transcoding process can create artifacts (no matter how slight). I'm assuming it's probably unlikely that you will be outputting to XAVC-L -- so eventually your edit system will be transcoding to your output format.

Do a real-world style test edit and see how your system reacts -- then you won't be surprised. But also test your transcode times for a full card of data! I have one client who wants not only my original camera footage but a prores copy as well before we leave location. Needless to say we're always waiting for that part to finish after we've packed all the gear!

[Chad Johnson]

I shoot everything in 30p unless I am going for slow motion, in which case I'll shoot 60p or 240p. I personally am not a fan of 24p, as I don't like the motion artifacts, and really 30p looks the same, but you can pan without judder. Shooting in 60p and editing in 6op results in a glassy look similar to video tape. Not filmic at all. Maybe if you are doing fast paced sports 60p is appropriate. Much of what I shoot ends up on TV (commercials), so 30p is right for that. In PAL land I would stick with 25p unless you plan on slowing down the footage, or if the client specifically asks for something different.

Also at 50p the appropriate shutter speed is 100, so you are robbing yourself of a lot of light. At 25p the shutter should be 50, and you will get away using less gain/ISO for a cleaner image, not to mention that every frame has more bits (2 times as much).

[Nigel Davey]

Thanks chaps. Useful feedback. I'll try my next small project/interview in 25p and see how that turns out. Chad why would I lose the extra 2 bits at 50p? Isn't it also 10 bit in XAVC HD?

[Chad Johnson]

What I meant was that if you shoot at 50fps at say 50mbps, you are getting half as many mbps per frame as if you shoot at 25fps at 50mbps. Does that make sense?

[Noa Put]

at 50fps at say 50mbps, you are getting half as many mbps per frame as if you shoot at 25fps at 50mbps.

That doesn't sound right, you are basically saying that 50p would then only be 25mbs, the data rate remains the same if you shoot 25p or 50p, only with 50p you get twice as much frames as in 25p.

[Christopher Young]

Noa. I think what Chad is getting at is that in XAVX-L you have 50Mbps of data per frame at 25p or 50p. In the case of 25fps that means you have 2Mbps data space for each frame. if you now record 50p with the same data rate, in this case 50Mbps you only have 1Mbps per frame as there are now twice as many frames to record using the same 50Mbps data rate.

For example a 64GB card in XAVC-L at 1080 50p gives you 143 minutes of data storage. 1080 25p still gives you only 143 minutes. With 50p being twice as many frames as 25p to be able to maintain the same data packing density the 50p should really be recorded at 100Mbps.

Likewise if you switch to XAVC-L 720 50p you still have 143 minutes on a 64GB card. If fixed at 50Mbps the difference here though is that the 720 50p has a much more efficient less compressed packing density than either of the 1080 flavors. At 1920 x 1080 in square pixels the pixels per frame storage requirement is 2,073,600 pixels per frame whereas at 1280 x 720 the pixel count is less than half at 921,600 per frame.

The way I understand it the math for HD is as follows

1920 x 1080 @ 50p = 103,680,000 pixels to store in 50Mbp of storage
1920 x 1080 @ 25p = 51,845,000 " " " " " " "
1280 x 720 @ 50p = 46,080,000 " " " " " " "
1280 x 720 @ 25p = 23.040,000 " " " " " " "

For the lowest compression and the best handling of very complex fast changing data 1280 x 720 is more efficient than either of the 1080 formats by a factor of x 2.
The above of course does not take into account other factors such as 4:2:0 vs 4:2:2 and 8-bit vs 10-bit encoding depths. Factors that again can have more or less impact on storage efficiencies depending on the codec and bit rates in question.

It's a different story if you look at Sony's XAVC-I implementation because if you go from 25p to 50p the data rate increases by a factor of x 2. In 1080 HD it goes from 111Mbps to 222Mbps.

Sony FS7 FAQ - Frequently Asked Questions

The fact that Sony, unlike any other manufacturer in H.264 Long GOP codecs, uses real time Dual Pass VBR in both its L and I frame variants and it's that which enables such good quality at these lower rates which is quite some achievement. We live in amazing times.

Chris Young
CYV Productions
Sydney

[Noa Put]

It's nice to know the mathematics behind it but what would be more interesting would be what it does matter in real life shooting. On my camera's I don't see any difference between shooting 25p or 50p when I visually compare the footage and by that I don't mean pixel peeping but to look at it from a normal viewing distance, the main difference I see is when I start to pan.

Nigel wanted to know if XAVC HD 1080/50p 50mbps vs XAVC HD 1080/25p 50mbps would make much difference in post, I think it's more important to realize what the consequences are when you shoot in 25p if you want to slow down the footage in post or if you shoot fast action scenes where faster panning is involved. That should be the main concern, not if 25p or 50p would make a big difference when stressed in post because my personal experience is that it doesn't but that is on a faster desktop machine and might be different on a slow laptop.

[Chad Johnson]

50mbps. That's 50mb per second no matter what the frame rate is. So shoving more frames into that second results in each frame having less resolution. Less resolution may not show much if you don't grade your footage, but push it a little and it breaks down. Not to mention you lose the amount of light hitting the sensor. But mainly, it just looks like video tape - all glassy. Nobody likes that look. You may as well shoot at 60i if you are trying to look like video tape.

[Noa Put]

Nobody likes that look

Well, about 100 clients I delivered to the last years would disagree on that statement. :)

So shoving more frames into that second results in each frame having less resolution

Can you show that in a few framegrabs that 50p results in less resolution compared to 25p? I"m not seeing it.

Not to mention you lose the amount of light hitting the sensor

I shoot at 50p at 1/50 shutter all the time so there is no loss in sensitivity compared to 25p, it looks exactly the same to me.

[Chad Johnson]

Did your clients ask for 60p footage? If they did, than that's what they want and 60p is appropriate. In my experience most clients don't know what's going on enough to discern between a filmic look of 30p vs a video tape look of 60p. That doesn't mean I shouldn't use my expertise to choose the appropriate settings.

I'm not going to do your research for you to prove what should be evident concerning bitrates and frame rates. Hey if you're happy with your methods, rock on. I'm just trying to encourage you to choose a frame rate for a reason rather than out of habit.

For one more example, our 100mbps 4k footage looks OK, but really the actual image is close to the quality of AVCHD. AVCHD is 28mbps at 1080p. Multiply that by 4 for UHD and you get a bitrate of 112mbps. To have the same quality (relatively) as the 50mbps 1080p30, the UHD would need to be 200mbps, like on the GH4.

It's just math. I'm not expressing an opinion here.

[Noa Put]

Here Chad, below video is a mixture of 1080p 50fps 28mbs avchd and 50mbs ipb mov and 100mbs 4K 25fps.

since you claim that 50fps looks like video and since there are plenty of shots in there that are either at 25fps and 50fps it should be easy for you to see the difference, no? Also, because math is all saying, could you also pick out a shot which is at 28mbs vs the 50mbs codec?

Vimeo

[Chad Johnson]

One more thought:

What is your timeline set to? If you shoot at 50p, but your timeline is at 25p, then the exported footage is going to look like you shot it at 25p, only the image quality takes a hit. In my example of 60p footage looking like video tape, that's only if your timeline and export settings are also 60p.

[Chad Johnson]

Here is a video that is both shot and delivered at 60p. Notice the glassiness?

Olympus PEN-F Sample Video - 1080/60p SuperFine Quality - YouTube

Look at the playback settings in the lower right of the video.