Lightbridge compression/bit rate ?

[Ale Reynoso]

Hi:
We took our Inspire to a test to find out how it performed as a live feed to an OB truck. We made it via an HDMI-SDI converter an tried sending 1080 50i and 720 50P to the truck. The engineers in charge were amazed about the stability and kind of shots that could be achieved, but said that the signal was "unacceptable" to broadcast live. They said they usually work with a bitrate of 1 to 1.5 Mb/s in wireless videolinks, and the Inspire 2 was "clearly under 0.5 Mb/s"...
Anyone has a clue regarding bitrates, compression and how to improve it? the "broadcast" mode was enabled. You could see some kind of "refresh" of the video signal every two seconds as a vertical scan from top to bottom that gave some weird aspect to the images. We tried a couple of connection alternatives, even switched converters, but never looked better.
Best regards

 

[Jason Woodcock]

Hi Ale what inspire are you using? Have you looked at Terradek we use the VidiU pro and no issues to date

 

[AMGPilot]

Lightbridge is a very low data rate low latency transmission, it's not really optimized for quality.

 

[Thatius Dudeson]

Lightbridge is a very low data rate low latency transmission, it's not really optimized for quality.

That would defeat the entire purpose of the system and you're the first person to say that... even the person above you says they have no issues with the correct adapters.

Sounds like there's codec mismatch between the Inspire and the broadcast hardware.

 

[Raphael Dahan]

Hi Ale what inspire are you using? Have you looked at Terradek we use the VidiU pro and no issues to date

Jason, are you satisfied of the Vidiu performance?
What setting do you use with that box?
Thanks in advance

 

[Ale Reynoso]

Hi Jason:
we´re using the Inspire 2 with the latest firmware. We are intending to use lightbridge integrated system. How do you use the Teradek in the Inspire anyway? there are not video outputs nor power connections to power it. It seems that the system is unusable for live broadcast (at least with a decent quality). If the system is designed that way, I think there is no way of improving data rates.​

 

[AMGPilot]

That would defeat the entire purpose of the system and you're the first person to say that... even the person above you says they have no issues with the correct adapters.

Sounds like there's codec mismatch between the Inspire and the broadcast hardware.

Ummm no such thing as a codec mismatch. In order for the Inspire to have a stable signal over long range they need to do one of the following, Have a high power transmitter on the aircraft (Which they don't) or reduce the data rate with compression and limited color space (8 or 6 bit on the color space) That's why they are slinging a 720p signal not a 4K. 4K to look acceptable (i.e. Youtube) needs 25Mbps the Cinema DNG output from the X5S is 4Gbps the ProRes is 1.3Gbps and the H.264/265 is 100Mbps. all of that is internal. The internal data rate for 1080 is 60Mbps a 1:1 down sample to 720p will net you a 26Mbps data rate. now if you go by Youtubes recommendations that 26Mbps rate has to be 5Mbps. the Lightbridge is probably doing a 5:1 compression (Which would be a normal compression rate for a transmitter) and that should be 1Mbps. Add a poor signal, some RF interference and add error correcting and you get to .5Mbps the equivalent data rate of 360P. Half 720p's recommend data rate. The "Vertical scan" comment is the clue that they had clean signal issues and the transmitter was working hard to keep the connection

 

[Ale Reynoso]

We had the "vertical scan" artifact even with the bird landed close to the receiver... Something wrong that could be cleared?
Not a single logical response from DJI representatives yet.

 

[NickU]

The vertical scan/refresh effect is also noticeable on the light bridge transmission proxy that the aircraft records on its sd card, so it's probably not being caused by poor transmission, but by something in the compression/downsampling. There's a helluva lot of work going on in the cinecore with at least two video streams being recorded simultaneously, and three if your recording to the SSD too, along with the light bridge feed and the fpv cam feed!

You can pull the files from the card and take a look - they're under a hidden folder called \misc\thm\100\ etc. If the light bridge quality is set to 1080 in the options then the file is recorded at 1080 too. When I played around with the broadcast settings a month or so back, they didn't seem to affect this file in any way as far as I can recall.

 

[Thatius Dudeson]

Ummm no such thing as a codec mismatch. In order for the Inspire to have a stable signal over long range they need to do one of the following, Have a high power transmitter on the aircraft (Which they don't) or reduce the data rate with compression and limited color space (8 or 6 bit on the color space) That's why they are slinging a 720p signal not a 4K. 4K to look acceptable (i.e. Youtube) needs 25Mbps the Cinema DNG output from the X5S is 4Gbps the ProRes is 1.3Gbps and the H.264/265 is 100Mbps. all of that is internal. The internal data rate for 1080 is 60Mbps a 1:1 down sample to 720p will net you a 26Mbps data rate. now if you go by Youtubes recommendations that 26Mbps rate has to be 5Mbps. the Lightbridge is probably doing a 5:1 compression (Which would be a normal compression rate for a transmitter) and that should be 1Mbps. Add a poor signal, some RF interference and add error correcting and you get to .5Mbps the equivalent data rate of 360P. Half 720p's recommend data rate. The "Vertical scan" comment is the clue that they had clean signal issues and the transmitter was working hard to keep the connection

We are talking broadcast here.... go back to youtube tutorials with that...

His tech guy could totally have the input settings out of whack, this isn't your desktop computer.

 

[AMGPilot]

We are talking broadcast here.... go back to youtube tutorials with that...

His tech guy could totally have the input settings out of whack, this isn't your desktop computer.

Actually you need to go back to your YouTube tutorials. There is no such thing as a "codec mismatch" with a live truck in broadcast I've been in the film/television and broadcast industry longer than you've been alive. A 720P HDMI output is going to be just that a 720P signal

 

[Thatius Dudeson]

Actually you need to go back to your YouTube tutorials. There is no such thing as a "codec mismatch" with a live truck in broadcast I've been in the film/television and broadcast industry longer than you've been alive. A 720P HDMI output is going to be just that a 720P signal

Call it whatever you want in your part of the world, but I use this feature all the time, no issues.

You can absolutely have your input settings different from output from the RC, give me a break.

 

[AMGPilot]

Call it whatever you want in your part of the world, but I use this feature all the time, no issues.

You can absolutely have your input settings different from output from the RC, give me a break.

Codec Means COMpression/DECompression and it only applies to recoding the image to media not transporting the signal to a OB truck. Yes a truck can input multiple broadcast legal resolutions But the truck doesn't define the data rate coming from the input. That data rate is defined by the input source.

You seriously don't know what you are talking about

 

[elmago75]

hey lets try to get a solution on this!! I´ve make the test in my home and its true!
A fucking vertical scan/refresh, that make my INSPIRE 2 totally
useless for broadcast live use.
That is a DJI selling points of this equipment, the big possibility of live broadcast in 1080p, 50fps or 720p, 60fps for professional porpouse . In fact DJI announces that. SO??
I´m just expecting to see a feed that seems aceptable in 720, but the poor bitrate make an awful image whit a gross horizontal line refreshing the image. No matter what the distance between the bird and control are, no matter what channel, frequency or transmission quality (less than 8mbps is horrible ) at 720 or 1080.
ALWAYS THE SAME VERTICAL SCAN/REFRESH at same period of time.
That´s not aceptable for an equipment that is on top of the products that DJI sells for filmmakers !!

 

[Raphael Dahan]

hey lets try to get a solution on this!! I´ve make the test in my home and its true!
A fucking vertical scan/refresh, that make my INSPIRE 2 totally
useless for broadcast live use.
That is a DJI selling points of this equipment, the big possibility of live broadcast in 1080p, 50fps or 720p, 60fps for professional porpouse . In fact DJI announces that. SO??
I´m just expecting to see a feed that seems aceptable in 720, but the poor bitrate make an awful image whit a gross horizontal line refreshing the image. No matter what the distance between the bird and control are, no matter what channel, frequency or transmission quality (less than 8mbps is horrible ) at 720 or 1080.
ALWAYS THE SAME VERTICAL SCAN/REFRESH at same period of time.
That´s not aceptable for an equipment that is on top of the products that DJI sells for filmmakers !!

Elma go hi, I tried to get an answer from Jason up there, he told that he is using the Terradek vidiuo pro, without any issues, I'm waiting his answer, if its real, the problems are solved ? Think so.

 

[Ale Reynoso]

Jason answer involves using extra equipment. But we don´t want to.
Mago, wich settings did you find regarding quality other than set to "broadcast"?

 

[Peter Jones]

Most likely frame rate mismatch between the truck and the HDMI o/p of the controller.

I had similar issues on the the I1 which only output 720P60 when the truck was using the more common (for broadcast) 720P59.94.

I ended up using a cross convertor/scaler to adapt the frame rate.
This is the unit I used. A-Neuvideo ANI-HPNH HDMI to HDMI Converter/Scaler.

The Teradek products mentioned will accept both 60 and 59.94 frame rates.

It's confusing but often when "60" is quoted it's often actually 59.94.

60 is a computer frame rate. 59.94 is a TV frame rate.

 

[Ale Reynoso]

We tried 1080i (50) and 720P (50). We checked the signal output in a TVLogic monitor and stated which signal was the remote sending, and it reflected the setting we were outputting (i.e. the display said 720 25P when outputting that and so on). The truck was a PAL country based, so there is not something like 49.98. We will keep tryig
Thanks!

 

[Ale Reynoso]

But Peter, was your issue this "refresh", vertical san artifact?

 

[AMGPilot]

can you shoot a video of the issue?