PXW X70 - 4K @ 50p & 120 mbs

[Mike Tew]

New X70 4K user
I have changed a X70 4K file from 25p & 60 mbs to 50p & 120 mbs

How - just used transcode in Sony Catalyst Browse
recoded to AVC/AAC (*mp4) internet 1920 x 1080 50p -
it worked, so then
recoded to AVC/AAC (*mp4) internet 3840 x 2160 50p -


I can count 50 frames for each second in my video.
Catalyst Browse data for the file show 50p & 120 mbs.

Sony Vegas project properties shows at 50p, - & I can count 50 frames per second - and plays file.

I plan to film juvenile Ospreys helicoptering over their nest [ first attempts at flight ] in 4K,
then crop to 1080p to get a closer image, but wanted 50p to show a smooth flying action.

Audio sounds OK - I can use the original tract if needed.

Hope to post test video's on You tube later this week

Could this file be transcoded up to 100p - 200p -400p - 800p -1600p -3200p
[ I am thinking slow motion playback ]

[Paul Hardy]

Sorry Mike, I don't want to put a dampener on your 'success', but what you have may be a 50fps file but it will NOT have 50 discreet frames, it will still only be 25fps, and each frame will appear twice.

Sorry to be the bearer of bad news!

[Paul Hardy]

Originally Posted by Mike Tew

I plan to film juvenile Ospreys helicoptering over their nest [ first attempts at flight ] in 4K,
then crop to 1080p to get a closer image, but wanted 50p to show a smooth flying action.

Thinking about it - if you're going to crop in to 1080p anyway, you might as well film at true 1080p50 & use the clear image zoom function - that way you'll still be zoomed further in & will have a true 50p recording for your slo-mo!!!

[Atticus Lake]

Originally Posted by Paul Hardy

Sorry Mike, I don't want to put a dampener on your 'success', but what you have may be a 50fps file but it will NOT have 50 discreet frames, it will still only be 25fps, and each frame will appear twice.

Totally true -- and in the same vein, increasing the bit rate from 60 to 120 won't give you any more information, you're just adding padding, in effect. It's like recording in HD and then upscaling to 4K -- sure, you get a 4K file at the end, but there isn't any more information; you're just duplicating pixels (or at best doing a crude interpolation). There's no technology in the world that can re-create information which has been lost.

Having said that, for slo-mo, you might find Twixtor helpful. It does very sophisticated motion analysis to create in-between frames in a moving image, so increasing the effective frame rate. It's not perfect -- it can't possibly be -- and you will see some warping, which increases if you go above 200% or 400% of the original frame rate. But still, it can be useful.

[Tom Grushka]

Unfortunately, it's true, and a simple experiment would confirm what Paul and Atticus are saying.

1. Find a low quality video on YouTube that seems to run at about 15 fps.
2. Copy the URL, go to www.savefrom.net, paste the link, and download the video.
3. Create a 50p HD timeline. Import downloaded YouTube video into timeline.
4. Render out to a 50p HD ProRes 4444 file.
5. Open and view the ProRes file, compare with the original, and notice absolutely no improvement in quality (and maybe even a slight loss in quality) and no new frames (even though 50p, it will still appear to run at about 15 fps or whatever the original was).
6. Pause and frame advance through the video. Notice the "missing" intermediate frames are just duplicate frames.

Or, for example:

1. Pick a number such as 1938592834.
2. Round ("compress") the number to the nearest ten-thousand: 1938590000.
3. Give the "compressed" number to a friend.
4. Ask the friend to guess the last four digits of the original number (....2834), without providing any hints!
5. Do this about a million times... well, maybe not!

That's an over-simplification of what's happening with lossy video compression in codecs such as AVCHD and XAVC. :)

[Mike Tew]

Hi, Tom, Atticus & Paul

Thanks you for your input, I now understand my trans-coding to 50p.
I will leave it up to someone at Sony to achieve an improved 4K for the X70.