N00b issue: video assist 4k / sony a7s

hi everyone,

bit of a potentially idiotic query, please do bear with me...

BACKGROUND:
i recently bought a BMD video assist 4k to enable the 4k capabilities of my 1st gen sony a7s.

i've managed to get this up and working and (after recovering from the shock of file size) have already started reaping the benefits of this larger source file size in editing phase. as i shoot almost exclusively in anamorphic (as a huge vintage projection lens with a vintage prime 'taking' lens), this is especially useful when needing to crop out occasional vignetting at narrow / closed down f-stops.

i have been having regular dropped frame problems despite buying 1 of the 2 recommended cards that were on this site a few months ago (transcend 64GB SDXC class 3 UHS-II), however since then i've noticed this list has been expanded and i'm now waiting on a lexar 2000X 64GB 300MB/s U3 V90 UHS-II SDXC to arrive from switzerland which i assume will address these frame drops with its faster write speed.


PROBLEM:
with the maximum fps at 4k on the a7s being 30, i now need to shoot some 60fps footage at 1080p with a view to re-interpret back down to my usual 24fps. my goal is to record this 1080p 60fps footage in ProResHQ to get the best that i can in terms of colour and depth.

my first problem (which may now be solved) was that i changed all the camera settings i thought necessary (disable 4k HDMI, retain HDMI export setting, change frame rate + using 180° shutter rule) but found that hitting 'record' on the a7s brought up an error message and failed to trigger the VA4k. someone in an FB group advised that, unlike when exporting at 4k, i would need an SD card in the a7s as well as the VA4k in order to trigger both successfully. tested this last night - all seemingly fine for triggering.

having bashed out a few short tests, in exporting the files from the VA4k card to my PC for editing i note that they've recorded instead at 30fps.

i went back to try again, this time seeing if it was a codec issue and so set to record simply in ProRes this time. same issue.

i note that the source on the VA4k screen is listed as being 1080i rather than 1080p as well, although it does seem to list correctly that it's 60fps on the screen. is this relative to the issue?

i'm almost 100% sure i'm being a total numpty here and apologies in advance for having missed something crucial and face-numbingly obvious.

cheers all!

H

Your Camera is not outputting 60 frames per second (progressive), it is outputting an interlaced (1080i) signal, so you are getting 60 fields (not frames) per second. It takes two fields to make up one frame. Interlace is how analog and early digital ca era worked to provide a signal that could be displayed on a CRT TV. So your 1080i60 signal will be a 108030p Video in a progressive time line on the NLE.

While the VA will record a 1080p60 progressive signal, your Camera will not output a 1080p60 signal. Sony and Canon crippled their lower and some mid level cameras. They want you to spend more $ to get their bigger pro cameras. The VA is only going to record the signal it receives, and only is able to convert an interlaced signal from cameras like the a7 from interlace signal (created in the ca era by using a pull down conversion) and convert it back to a progressive signal, if you have “remove pull down” selected in the menus. So a 1080i60 signal goes back to a 1080p30 signal (which it was before the pull down conversion) and then record it as 1080p30.
Cheers

Your Camera is not outputting 60 frames per second (progressive), it is outputting an interlaced (1080i) signal, so you are getting 60 fields (not frames) per second. It takes two fields to make up one frame. Interlace is how analog and early digital ca era worked to provide a signal that could be displayed on a CRT TV. So your 1080i60 signal will be a 108030p Video in a progressive time line on the NLE.

While the VA will record a 1080p60 progressive signal, your Camera will not output a 1080p60 signal. Sony and Canon crippled their lower and some mid level cameras. They want you to spend more $ to get their bigger pro cameras. The VA is only going to record the signal it receives, and only is able to convert an interlaced signal from cameras like the a7 from interlace signal (created in the ca era by using a pull down conversion) and convert it back to a progressive signal, if you have “remove pull down” selected in the menus. So a 1080i60 signal goes back to a 1080p30 signal (which it was before the pull down conversion) and then record it as 1080p30.
Cheers

damn and indeed blast.

maddening since the a7s records at 1080p60 internally just fine and it works brilliantly for slow mo.

it's moments like these that i find myself wondering after a potential hack of sorts. how annoying!

H

apologies to be difficult, but i've found this info on a page listing the full spec for the sony a7s 1st gen:

The full list of supported HDMI output signals is:

3840 x 2160 (30p/24p)
1920 x 1080 (60p/24p)
1920 x 1080 (60i), YCbCr 4:2:2 8-bit/RGB 8-bit

which suggests this could actually be a thing at 60. this is on the B&H product page.

B&H product page is not always accurate. Check your Camera Manual or the Sony site.
You have already checked the HDMI out setting, and set the camera to 1080p60, and you can check to see if the VA shows the camera is outputting a 1080i60 signal (upper left corner shows signal resolution, and frame rate). Your previous post indicated it was showing 1080i60 as the signal. Regardless of what some specification says it supposed to do, this is what the camera is actually doing.
Cheers

sincerest apologies.

you know how i was saying it was likely me being a complete plonker on a simple issue? looks like i've found it.

there's actually a sub-menu point on the a7s HDMI resolution settings that you can toggle between i and p. for some reason, mine was automatically set to i.

changed it to p, tested it out just now all seems to be working rather well.

thank you for the help by the way, denny. valuable lesson there in what interpolation does to the signal.

H

You are welcome, that is why I suggested looking at the HDMI menu and having a second go at it. Glad you got it sorted.
Cheers