How to deal with 50p footage

[Dave Baker]

OK, so I have a camcorder that will shoot 50p footage, not so unusual I guess, but how do I deal with it when I have shot it? I have no specific use for 50p footage as it is, it needs to be 25p for me to view it.

As I understand it, if I shoot 50p and convert it to 25p, either for editing or during rendering, I am throwing away half the bit rate, which suggests shooting 25p would be better in the first place. Is there a way to convert 50p to 25p without bit rate loss, that I have not yet found?

Currently I shoot 25p, which means I have 50p available as overcrank for slomo and I can use 50i for fast motion. I am reasonably happy with that, but this is a question that has been bothering me for a while.

Dave

[Rainer Listing]

If it's any comfort to you, apart from slo-mo I haven't found a use for 50p either. For normal motion, I think you're better off shooting 25p for the web, 50i for disc for smoother motion. Shooting 50p and displaying 25p, any editing software I know you lose half the frames and end up with around half the bitrate, don't know there's any way around that.

[Dave Baker]

Thanks Rainer.

I started off with this camcorder shooting 50p @ 35mbps because people were raving about the image quality of 50p footage. How they were viewing it I don't know, but I wasn't so happy with it after the initial euphoria of playing with my new toy. After a bit of testing I came to the conclusion that I preferred 25p @ 24mbps. On my cam, 35mbps HAS to be 50p.

Naturally I want to get the best out of it, so I thought I would ask if I am missing a trick. Now I know I am not the only one who has no use for 50p as a standard shooting option and I am not missing some process I haven't heard of, I feel happier.

Dave

[Mark Whittle]

What NLE are you editing on, Dave?

What types of things do you shoot, and what are you outputting to?

For example, if I'm shooting a talking head for web delivery, I'll shoot 25p.

If I'm shooting the outdoor photo shoot part of a wedding, I'll shoot 50p. (Weddings end up on Blu-ray 1080i25). This gives me the option to slo-mo 50% with all the frames intact when I open the 50p clips in a 1080i sequence. Otherwise it plays back smoothly at normal speed (Premiere CC in my case), much smoother than 25p.

For the wedding speeches I switch to 25p to get a little more light in with a 50 shutter. I'm an old-school ex broadcast man so I am very used to the interlaced look, so 25 or 24p can look a little jerky to me. There is no 25p blu-ray @ 1080 so its either 24p or 25i for that output.

If you're doing all web stuff, avoid interlaced altogether.

[Dave Baker]

I shoot an eclectic mix ranging from landscapes and wildlife to aircraft by way of steam trains, ancient monuments etc. etc.

I edit in Kdenlive and output .mp4 which I put on either hard drives or USB sticks and if posting on the web, some I reduce to 720p for Vimeo, others I upload as is to Dailymotion. I have been transcoding to DNxHD 10-bit 4:2:2 for editing but, having just discovered a flaw in my method of archiving footage, something which, embarrassingly, I should have checked a long while ago, I have just changed to proxy editing. I am finding some unexpected changes which I think are for the better.

I prefer to shoot progressive, I have yet to shoot an event that needed interlaced. I mean, if I'm panning to track an aircraft passing fairly low at, say, 400mph, who the heck is going to notice any skew in the background? And would they care anyway?

Dave

[Rainer Listing]

Originally Posted by Mark Whittle

50p ....much smoother than 25p

(when rendered to 25p.)

Hi Mark, I keep hearing this, but watch and pixel peep as I might for the same shutter speed, I can't see it. Nor can I work out any reason why this might be. Do you know? I mainly use Vegas Pro 12.

[Mark Whittle]

Hmm, for some reason my last post didn't appear. Maybe because I sent it from the mobile.
I was responding to Dave's comments about skew in the background. I am not sure what you mean, Dave. It is about capturing more frames per second for smoother motion. Interlacing is effectively more frames per second, as each field is from an earlier point in time than the next.

I use Premiere CC and Avid MC. Our Avid is a few versions behind so everything has to be conformed to 25i , but in Premiere I put it directly onto a 1080i25 sequence and it plays back smoothly at normal speed. This means Pemiere is turning every frame into fields (25i = 50 fields). Yet if I want slo-mo I just make the clip 50% in the sequence and I get beautiful smooth slow motion. 25p looks OK until there is panning or rapid movement, then you get the staccato jerky look that I don't like (30 year habit of editing interlaced stuff).

50p looks great because although it gets turned into interlaced on the timeline, the two fields of each frame are identical, i.e., no temporal difference.

With Avid it has to be conformed as 1080i so the slo-mo benefits are gone. Not sure how Vegas or other NLEs handle it but if they are latest versions they should deal with it properly.

Rainer - I'm not sure what you mean - pixel peep? What are you expecting to see?

I should emphasise that my needs are for Blu-ray output, which requires either 1080p24 or 1080i25. There is no 25p @ 1080 for Blu-ray. If you're only outputting for the web or computer monitors, avoid interlaced formats. They can't display them properly.

[Dave Baker]

Hi Mark,

By "skew" I was referring to the rolling shutter effect, I was pointing out that I have yet to find a need to shoot interlaced and that I understand faster frame or field rates make motion appear smoother. I was also (somewhat obliquely I admit) suggesting that if the subject is well framed and sharp, the viewer should have no need to look at the background, whether it is skewed or not. Also with the shutter at 1/50th, 25p makes the object appear to be travelling faster. But that's going off at a tangent.

Maybe I should qualify my original question thus: The maximum bit rate this camcorder gives is 35mbps, but it will only shoot 50p at that rate. The best rate for 25p is 24mbps. We all know that a higher bit rate means less compression, therefore higher visual quality, ergo it is better to shoot at 35mbps than 24mbps. If I shoot at 35mbps, I have 50p footage I don't necessarily need.

Now, unless I am misunderstanding this, if I convert 50p to 25p for editing, I am throwing away half the bit rate i.e. effectively shooting 25p at 17.5mbps. I have to say that 25p shot at 24mbps looks better to my eye than 50p reduced to 25p. So what I am asking is, is there a way to losslessly convert 50p to 25p so I finish up with 25p at 35mbps that I don't know about. If there isn't I can live with it but if there is, I'd like to know.

Apologies if the original question was not clear enough and thanks for helping.

Dave

[Noa Put]

unless I am misunderstanding this, if I convert 50p to 25p for editing, I am throwing away half the bit rate i.e. effectively shooting 25p at 17.5mbps.

I"m sure this can't be right, the lower bitrate you shoot at the more artifacts will start to appear especially when there is a lot of motion. But when you shoot at the highest possible bitrate in 50p and edit it on a 25p timeline this only has an impact on the number of frames per second, not the bitrate, that will remain the same based on what bitrate you choose when you render the file.

[Mark Whittle]

Hi Dave,

The rolling shutter issue has nothing to do with frame rate as far as I know. I agree about the background.
I tend to shoot with a shutter at twice the frame rate to emulate the 180 degree look we're used to.

I wouldn't worry so much about the numbers and pixel peeping and a lot of stuff you read about online. Trust your eyes and go with what you like. The bit rate issue is kind of the same thing. Who cares? My camera shoots at 50 Mbps or 72 Mbps. Most people agree that the 50 Mbps looks better in this case because the implementation is more efficient (IBP vs all I frames) so bit rate isn't everything.

Your camera (a Sony I'm guessing?) needs 35Mbps to record 50p as there are twice as many frames per second to encode.

You're not throwing away bit rate; you're "throwing away" half the frames, similar to converting a stereo file to mono: you lose half the information but the bit rate & resolution of the file remains. Some NLEs handle this better than others. I don't have any experience with your NLE so can't help there.

I'm not an expert on this stuff, just been doing it a long time, and as soon as any maths is involved I turn into a total dunce :) But I agree with Noa here. Until you render to another format it is still what it was when you shot it. I thought you said you transcode to DNxHD. Your original bit rate will increase to whatever flavour of DNxHD you choose.

[Dave Baker]

Originally Posted by Noa Put

But when you shoot at the highest possible bitrate in 50p and edit it on a 25p timeline this only has an impact on the number of frames per second, not the bitrate, that will remain the same based on what bitrate you choose when you render the file.

And from Mark -
"You're not throwing away bit rate; you're "throwing away" half the frames, similar to converting a stereo file to mono: you lose half the information but the bit rate & resolution of the file remains."
That about covers it! I wondered if this was the case, but did not want to jump to any conclusions.

I still think 25p at 24mbps looks better than 50p reduced to 25p though, which one reason I asked.

No Mark, the camera happens to be a Canon.

I had been transcoding to DNxHD until a few days ago, putting either 50p in and getting 25p out or lately, 25p in and out. I tried setting DNxHD for 50p out to compare, but 50p at around 260mbps just choked everything and rendered footage was jerky on playback. I consider that the reduction in DNxHD from 50 to 25fps may be the problem and I need a different way, which is another reason I asked. (50p rendered from the original .mp4 files plays back perfectly well and looks better). It's not that DNxHD reduced footage is bad, it's not, but I know I can do better.

I changed to proxy editing a few days ago. I tried it some years ago in Vegas and didn't like it, but in Kdenlive it works well for me and I am getting better results.

Thanks for your help.

Dave

[Mark Whittle]

Yes I get better looking motion in Premiere than our transcoded DNxHD in the Avid. It just looks jerky somehow. Not very technical I know but it just doesn't look right.

Wow 260 Mbps. A bit of overkill? What's wrong with 36 or even 120? You're just filling up your drives for no gain. Do you have a fast RAID array? If you are playing out from a single drive at this rate that could explain your playback issues. Your system can't keep up and is possibly dropping frames.

I know nothing of Kdenlive so can't comment on its abilities but being open source it is possible it is behind a bit with modern H.264 based codecs.

[Dave Baker]

Originally Posted by Mark Whittle

Wow 260 Mbps. A bit of overkill? What's wrong with 36 or even 120? You're just filling up your drives for no gain.

It may not be the exact figure, but it was around there. DNxHD has specific bit rates for specific encoding options e.g. 1080p 25fps can be either 120 or 185mbps, 30p is 145 or 220. Change the bit rate from those and it simply will not work. When I was changing the script to obtain 50fps, I started at 185mbps and slowly increased it until I found a rate that worked.

Out of interest, I did a comparison a while ago between a NeoScene encoded Cineform file and a DNxHD encode of the same, the DNxHD encoded file was substantially bigger than the Cineform file.

Because Kdenlive is Open Source, if the codecs are available and you know how (I have hardly scratched the surface), it can be made to do almost anything. For example in the Rendering box, the command line for the selected output type can be shown and can be changed to suit yourself, then saved as a template if desired. If wanting to edit 4K, it's easy to write a new project profile to suit. Taking it a stage further, anyone can download the source code and modify it as they see fit. I wouldn't like to say whether it is behind or ahead, but everything is available for it to be fully up-to-date.

I've been playing around with some 50p footage without DNxHD and it looks better, it has more "polish". Now to figure out which way to go with it.

Dave

[Noa Put]

Don't think there are many users here that edit on Linux with Kdenlive, I just edit 50p in Edius, throw the native files on a 25p timeline and render out to either a mp4 file as HD master of for the web or a hqavi file to either go to a blu-ray or dvd and it all looks good to me. Have you tried editing in lightworks?

[Dave Baker]

Hi Noa,

I asked if anyone here was editing on the Linux platform, the only replies (2) were asking about Lightworks. Why? As far as I can see, the Lightworks port to Linux is a fairly crippled version and that doesn't interest me one bit.

I tried the most promising of the available Linux NLEs and settled on Kdenlive before the Linux version of Lightworks appeared. I used to edit in Sony Vegas until I finally came over to Linux to stay and I have to say, I prefer Kdenlive, which does everything I have asked of it so far.

Thanks for your help.

Dave