Receiving ISS Ham TV

[Phil M0DNY]

Dave and I spent some time today looking at the Video from HAMTV, attempting to get an idea of what video aspect ratio to expect from the Camera.

I've got some information collected here: philcrump.co.uk/ISS_HAMTV

In Summary: We think the camera may be 16:9, transmitted as squashed 4:3 (720x540), with incorrect 3:2 (720x480) description in the TS headers.

Phil M0DNY

[F6DZP]

Hello,

We think the camera may be 16:9

Sure, the DV camera is in 16:9 mode.

with incorrect 3:2 (720x480) description in the TS headers

No: 720x480 is the correct description for 16:9 D1 standard

The TS transmitted by HamTV is in 16:9 format NTSC_D1 = 720x480.

720x480 is the D1 picture size that gives a DV camera set in 16:9 _ NTSC
720x480 is the D1 picture size that gives a DV camera set in 4:3_ NTSC

720x576 is the D1 picture size that gives a DV camera set in 16:9 _PAL
720x576 is the D1 picture size that gives a DV camera set in 16:9 _ PAL

The camera onboard ISS gives a composite NTSC 16:9 signal
.
In the D1 standard "Video world" we don't have "square" pixels like in the computer world.

720 pixels are digitized for each line in both modes and the choice of 4:3 or 16:9 gives us the way we must show the picture.
( if you look at the DV encoded file from a DV camera you will see 720x480 pictures encoded with a Mjpeg codec . If you change the 4:3 mode in 16:9 mode, you will see the same amount of "rectangle" pixels by line : always 720!
This is only the "length" of the rectangle that changes)

So when we want to display a 720x480 Mpeg2_16:9 encoded signal, we show on a computer (= "square" pixels) 854 pixels by line.

The Minimod Mpeg2 encoder inside Hamvideo is set in D1_NTSC format, so it gives us 720x480 pictures digitized from a 16:9 NTSC analog signal with 480 lines
BUT THE 16:9 flag has not been set!

HamTV TS format analyze.jpg (88.27 KiB) Viewed 7822 times

You can see that we stay with the 4:3 display format. So, by default, VLC and other rendering systems will show us a 4:3 picture if we don't force them to the 16:9 display format.

HamTV TS video and audio format given by VLC.jpg (122.98 KiB) Viewed 7822 times

In ISS mode, Tutioune knows that we are in 16:9 display format, so shows us 854x480 pictures as it must do. ( EDIT : NO, using today version Minitioune shows a 3:4 picture inside a 16:9 black rectangle, see the explanation in my next post)

When a video is digitized, we cannot know the format of a picture by looking only the number of pixels by line and the number of lines.
a 480x480 encoded picture can be a square, a 4:3 rectangle, a 16:9 rectangle or anything else....

The video of Koichi Wakata I have recorded and put on Youtube is shown in 16:9 format.
https://www.youtube.com/watch?v=EpFzbKvK1pk
You can see the difference with the same video shown in 4:3 format
https://www.youtube.com/watch?v=61GTGTOa8AE

Jean-Pierre F6DZP

[Phil M0DNY]

Ok, the non-square pixels do help a lot! I've done some more reading..

At the Transmitter:

The 16:9 camera signal has been squashed into NTSC_DV, at 720x480. This is subtly resized from NTSC_D1, which is 720x486, for Digital capture (so that the pixel dimensions are divisible by 16).

At the Receiver:

NTSC_DV & NTSC_D1 pixels have an aspect ratio (PAR) of ~0.91 (width/height, making the pixel tall and thin). So for accurate display on a square pixel monitor we can upsample the height (or downsample the width), for a resolution of 720x540 for 4:3. (or 640x480 for downsampling)

Which would be stretched back to 940x540, (or 854x480) to restore the 16:9 of the camera! (Edit: Or of course, stretch, then downsample..)

Got it now... although I still don't understand why the blue line on the blank HAMTV transmission is displaced into the left of the image compared to the unstretched TS played in VLC?

Edit 15:18: Corrected maths on aspect ratios.

[F6DZP]

Hello,

I still don't understand why the blue line on the blank HAMTV transmission is displaced into the left of the image compared to the unstretched TS played in VLC?

I have spent more time to understand what happens:

- the camera is set in 19:9 format and we use the composite output.
- the Mpeg2 encoder digitize and encode a 720x480 picture size video, but the 4:3 aspect ratio is indicated in the TS
- STB or PC using software will want to display in 4:3 format

In Tutioune/Minitioune I force the display to be in 16:9 (854x480 or 960x540), BUT the Microsoft renderer continue to display a 4:3 format inside a 16:9 picture, so we have a 4:3 video with 2 black vertical zones at each side and the left black zone has a vertical blue line that show the separation.

It was difficult to really understand what happened, because HamTV has no camera plugged, so no signal to digitize.

Last year when we have made the test receiving HamTV, Tutioune was used only for receiving/measuring, correcting and recording the TS. The renderer used was VLC (receiving the TS via UDP) set in 16:9 format with Vcam set in 16:9 format(854x480) and FMLE set in 16:9 format 854x480 for streaming to the BATC server.

So, we have never yet used Tutioune/minitioune for rendering. It is only with the last version of Tutioune/minitioune that I try to render the video inside Tutioune/minitioune, but had only black picture from blank transmission.

Yes I have seen early that I had this blue line in Tutioune/Minitioune display, but knowing that there was no signal given to the mpeg2 encoder, supposed it was a strange data/noise? taken by the mpeg2 encoder that has nothing to digitize, and without any true video to look at, it was not easy to find what exactly happened.

So today, if we want to display a good 16:9 picture, we have always the solution to use VLC forced in 16:9 format.

I will work on that immediately to find a solution for rendering a good 16:9 aspect ratio inside Tutioune/Minitioune.
I apologize for that inconvenient in Tutioune/Minitioune display and I will fix that as soon as possible.

Jean-Pierre F6DZP

[F6DZP]

Hello,

I have now a new version of Minitioune that can allow to change the aspect ratio from 4:3 to 16:9.

Minitioune v0.3b
If you want to test it, send me a mail.

I will put it for download today.

Jean-Pierre F6DZP

[F6DZP]

The new Minitioune version is available for download.
http://www.vivadatv.org/viewtopic.php?f=60&t=452

You will have now the 16:9 video with the good Aspect Ratio.

The mpeg2 video is coded with a 720x480 definition, as it is defined being 4:3 format, the decoder gives a 720x480 video to the Renderer set for 720x540 forced in 16:9 format , as it is in reality a 16:9 video, photo in Minitioune are taken with the 960x540 definition and video in Minitioune can be set to 629x354 or 1024x576 or more, depending of the zoom setup..

Jean-Pierre

[G4EWJ]

For the last few days, I've been getting 'Goonhilly Dishcam offline' on the ARISS dashboard. If I refresh Chrome, I see the dish briefly before getting the message again. It seems to be an up to date frame, as the dish is moving as I expect. This also happens with Explorer. I'm using W7-64.

It's happened a little on Chrome for Android, but it's fine at the moment.

Brian

[G8PUO]

Best wishes to the team at Sandringham School, the stream is looking good from https://principia.ariss.org/Live/ and excellent dash https://principia.ariss.org/dashboard/.

Well done to all involved and look forward to the ISS pass.

[Phil M0DNY]

For the last few days, I've been getting 'Goonhilly Dishcam offline' on the ARISS dashboard. If I refresh Chrome, I see the dish briefly before getting the message again. It seems to be an up to date frame, as the dish is moving as I expect. This also happens with Explorer. I'm using W7-64.

Hi Brian,

The brief image of the dish is a glitch that happens as the page loads - it then switches to the offline holder if the loaded image is more than 10s old (indicating the live upload has failed).

If you could catch me on skype when it happens again (phildcrump) - that'd be very useful. I monitor it myself a lot but different OS/browser combinations can highlight issues.

I've got a fix for the startup glitch, it'll be up once I've finished working through clear-up from yesterday.

Phil

[G8PUO]

Well done on the dash, super work!