One Summer Evening with the FS700

[Alister Chapman]

You might be right Noah. I'll check again when I have a camera at the end of the week.

[Cees van Kempen]

Originally Posted by Alister Chapman

Yes, that is correct. It would be the equivalent of 120fps with a 180 degree shutter or 1/240 shutter.

I suppose this means that it would be possible to schoot 240fps with nanoflash and other devices, if Sony would include the option to write the files at a speed of 30fps instead of 60fps? Any chance that this might happen?

Is it by the way confirmed that the output over sdi is before compression?

[Arnt Mollan]

My guess is that the speed/loop recording is done after video is coded to avchd, to use less memory. If so, that means we could not record slowmo to extern recorder through the SDI port. Only to intern memory. No better quality.
Isn't it also so, if 1080p50 is recorded at 28 mbs, and put on a 25/24p timeline, we use only half the pictures, and the effective mbs would be around the half? Thats 14 mps! The same happens if we stretch the footage to 25/24p.
If used from camera, or from a TV/PC that can play back 50 or 60 frames it can look fine.
But my delivery is mostly broadcast, and DVD projects at 25p. The footage from my nx70 recorded at 1080p50 looks worse than footage recorded at 25p. But I have not measured the bitrate.
Or am I thinking wrong here?

[Cees van Kempen]

Arnt, Alister Chapman proved already that the FS700 sends the slomo over sdi to external recorders. The Gemini takes full advantage of the 240fps and the nanoflash only half. See his explanation before in this thread. He supposed in other threads that is is before compression, I am looking for confirmation of that.

[Frank Glencairn]

Yeah, AVCHD compression takes place in the moment the buffer writes to the card.
But the 8bit 4:2:2 signal is active at the SDi and HDMI ports at the same time.

It would take a hell of computing power to apply compression at 240 FPS.

Frank

[Matt Davis]

Here's a controversial sideways thought about that.

1080p50 material at 28 mb - I don't think, because of the way that H.264 and AVCHD work, we can do a straight halving. The extra bitrate can be spent on looking at the (less) difference between frames. There are also 'jumps' in MPEG2 recording, in that the difference between 25 mbit and 35 mbit was quite extraordinary (thinking of XDCAM here).

Best PAL SD comes from 720p50 (or 720p25 if you don't want interlace). I've stuck with this since getting an EX1, and BBC has published guidelines, test results and the like. You'll have to blur 1080p before downscaling to reduce the amount of detail to avoid aliasing. You'd certainly avoid shooting 1080i for SD, as you'd have to de-interlace (thus reducing resolution by 25%) before scaling, and then you'd loose the temporal information OR you'd use fields as frames and find that 540 lines is less than 576, and accept the lumpy scaling UP.

The AVCHD codec implementation in the FS100 and FS700 is really good. Very good indeed. I would pitch it against XDCAM-EX 35mbits and expect it to look wonderful. Only the usual 'Compression Nightmare' suspects will degrade it: scenes with lots of movement throughout the screen - full screen water, a viewfinder full of leaves in the wind, certain types of sports shot.

Various testers have looked at the FS700 SSM and all agree that in order to perform this magic at that money, the SSM modes will have to include a little aliasing just to read off the frame data quick enough. This will happen and can be outputted to a 4:2:2 device like the Gemini, but the sole act of the expediated sensor read will have done the damage. Want more? Want better? Get a Phantom or an Epic. :)

[Cees van Kempen]

Originally Posted by Alister Chapman

It's going to have to be 50 or 60p. Not many will want to wait 80-90 seconds before being able to shoot another shot. The Gemini and Hyperdeck Shuttle 2 can do it. My full review is online now A Second Look at the Sony NEX-FS700. | XDCAM-USER.COM

Alister, are you sure the Hyperdeck shuttle 2 can do it? When looking at the specs I only see a normal HD-SDI input, not 3G. Don't you mean the Hyperdeck Studio?

[Tim Polster]

For thought comparison, how much better do you think the FS-700 slow-mo is than using Twixtor with 60p material? Or is it?

Workflow, shooting and image quality?

Thanks for your input.

[Noa Put]

Without having a fx700 I would say it will be MUCH better, all twixtor slowed down 50 or 60p footage I have seen produces some weird morphing artefacts that you won't get with the fs700.

[Noah Yuan-Vogel]

Twixtor'ed 60p:
Pro: Looks pretty good if you're shooting subjects that are interacting with low/no-detail backgrounds, allows simulation of very high overcranking
Con: Edge artifacting in most normal situations with significant motion, long render times, lots of time and tweaking required for each shot for optimal results which is still always inferior to real overcranked footage

FS700
Pro: No interpolated edge artifacts, no extra hours of plugin tweaking and rendering to get an inferior result, can playback on set to see and evaluate footage
Con: Costs more than twixtor, burst time limits


There is no replacement for actually shooting high framerates.

[David Heath]

Originally Posted by Matt Davis

Here's a controversial sideways thought about that.

1080p50 material at 28 mb - I don't think, because of the way that H.264 and AVCHD work, we can do a straight halving. The extra bitrate can be spent on looking at the (less) difference between frames.

Not controversial at all! And not just to do with H264 and AVC-HD. It's highly likely that with 1080p/25 and 1080p/50 the time difference between I frames is the same (1/2 second?) and hence the same difference between them because of movement.It follows that for 1080p/25 the GOP length is 12, for 1080p/50 it will be double that.

Since I frames need a lot more bits than difference frames, it's then easy to see that doubling the basic frame rate won't need anything like a doubling of bitrate. Practically, there's a lot more to it than that - the content differences between successive difference frames will be less (only 1/50sec apart, rather than 1/25 sec) so the coded size of each can be smaller with 50p than 25p. That will help compensate for the greater number of them.

There are also 'jumps' in MPEG2 recording, in that the difference between 25 mbit and 35 mbit was quite extraordinary (thinking of XDCAM here).

Again, not unique to MPEG2. You need a certain minimum bitrate to get anything worthwhile at all, any increase then gets applied just to reducing deficiencies - and if they weren't that bad in the first place......

It's part and parcel of the same argumentabout the oft (mis)quoted statement about H264 offering half the bitrate of MPG2 for equivalent quality. It's true - but only at quite low bitrates. The H264 "tricks" do improve on areas where low bitrate MPEG2 shows problems. But improve the MPEG2 bitrate and there's less problems for H264 tricks to work on!

Hence H264 has big advantages or broadcast transmission and web video - less point for camera acquisition where bitrate is less of an issue.

[Alister Chapman]

Originally Posted by Cees van Kempen

Alister, are you sure the Hyperdeck shuttle 2 can do it? When looking at the specs I only see a normal HD-SDI input, not 3G. Don't you mean the Hyperdeck Studio?

You are correct Cees. The Shuttle 2 cannot do it. In BMD's press release they say it can, when in fact it can't.

[Noah Yuan-Vogel]

To be clear, though, it sounds like we could record 240fps and still get 120fps frame decimated footage out to a non-3g recorder like the hyperdeck shuttle 2 or other device? This would be done by setting our recording format to 30p (since 60p requires 3g) and when writing out the buffer every other frame is still played out of hdmi/hd-sdi. Can someone confirm this?

[Chris Medico]

As soon as my camera arrives I will test this idea.

[Tim Polster]

Thanks for your input on Twixtor. Just wondering how the time limit on the FS-700 slo-mo works into a workflow with such a short burst. Making a clear choice between slo-mo or live might be difficult.