59.94fps & deinterlace conundrum with BenQ, Extron, and cheap ATSC converters

Hardware Other Hardware
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So BenQ in their infinite wisdom decided Bob deinterlace was the best method to deinterlace, when most other manufacturers decided motion adaptive deinterlace is superior and actually better, like ViewSonic. Got their EX2510 and apparently that was how they decided to do deinterlace…

The other problem is the ATSC Tuner I just got (a Proscan PAT102-B/D) has motion adaptive deinterlace, but outputs 60.00hz in 720p and 1080p instead of the industry standard 59.94hz for NTSC. This means dropped frames or mistimed frames every 60000/1001 frames or so. The rest of the time it’s perfect with frame time consistency, but because of the mismatch, it runs into this issue.

Fortunately some people have looked into the firmware for these receivers and found you can actually modify it. I just don’t have the know how to correct the 720p and 1080p modes to 59.94hz. 480i and 1080i though are proper 59.94hz.

http://www.devttys0.com/2012/08/reverse-engineering-a-dtv-converter/

But the alternative is I get a HDMI to HDMI deinterlacer like the Extron DSC HD-HD. The biggest problem is static elements in a bob deinterlace function on a high refresh rate display causes severe temporary image retention. This wasn’t a issue with lower refresh but is a HUGE issue with high refresh displays and BenQ should have had a better deinterlace like ViewSonic.

This is being stuck inbetween a rock and a hard place. Pull the firmware and modifying the Proscan firmware through UART or a BIOS chip clip? (would fix 720p channels and skip a interlacing step) Or get the Extron scaler which is overkill for a $30 converter box, and would effectively deinterlace a 720p signal twice? (no station in 720p where I live is native 720p, they are all deinterlaced from 1080i)

Not many people pay attention to 59.94 vs 60.00. Also, Linux can’t even detect the 120.00hz mode on this monitor, (only the 119.88hz mode) but Windows can!

Side note, the upcoming Retrotink 5X also uses bob deinterlace with 1080i so it’s no better. It would also have to go through the Extron DSC HD-HD for 1080i. OSSC Pro should support it, but it’s an arm and a leg and not released yet.

If there’s no easy solution, I have to make a video warning people not to use bob deinterlace on high refresh panels.

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Ok, this is 100% my wheelhouse, but I want to make sure I understand the issue.

You have an ATSC 1.0 tuner, that outputs 1080p @ 60, but your monitor cant take that?

3

No, the frame times are inconsistent. It will jump frames every 60000/1001 frames either forward frames or duplicating 1 or 2 frames.

4

I understand that part of the issue, I am trying to understand where/why its happening in your signal chain.

If the tuner has motion adaptive deinterlace and outputs 1080p60 to a TV or computer monitor everything should be fine. If you are trying to force the TV/Monitor to 1080p 59.94 then yes you would get a missmatch because the tuner is not producing dropframe.

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No, the Tuner is refusing to output at 59.94 in progressive no matter what destination hardware you use. It’s programmed to 60.00 for all progressive modes. This is the problem, because it will mistime every 60000/1001.

Proper tuners like Motorola Cable STBs adhere to 1080p 59.94.

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right, but if the screen its connected to accepts 60hz non-dropframe then there should be no issue. So unless the tuner is not doing a true deinterlace and is embedding the timing missmatch everything should be working.

ignore the standard for a second, and look at each handshake.

Air to Tuner 59.94 (fields, drop frame) Tuner to TV/Monitor 60 frames non-dropframe. So unless the output of the tuner is not actually 60 it should be a constant signal between tuner and TV/Monitor.

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The tuner chip on the HDMI output refresh timings end set the refresh rate to 60.00 but all broadcast is 59.94, so it’s trying to framerate scale and it’s not doing a good job when it hits time it has to drop a frame. The 1080i mode though adheres to 59.94.

This is not a issue with the monitor, it can take whatever it wants, but the tuner is being stupid in outputting 60.00 when it should be outputting 59.94. It is not an EDID issue as fixed resolution tables are baked into the firmware.

If you’re asking about how the tuner decodes 59.94 to 60.00, the hardware decoder chip was designed with 59.94 in mind, not 60.00. So the firmware was misconfigured setting the HDMI resolution table progressive output out of sync with the hardware decoder.

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So if I understand correctly, for the devices,

  • Antenna: all stations being received are 1080i
  • ATSC Tuner: Proscan PAT102-B/D
  • Monitor: BenQ EX2510

Your issue is,

Antenna → Monitor

Not possible, BenQ EX2510 only has HDMI and DisplayPort input, no builtin tuner

Antenna → ATSC Tuner → Monitor

ATSC Tuner set to output 1080i

Ugly deinterlacing — you think the monitor is using a suboptimal (Bob) method.

ATSC Tuner set to deinterlace

Good deinterlacing, but now frames are being regularly doubled/mistimed because the aerial signal (59.94 Hz) is being converted to 60 Hz.

My thoughts

A properly deinterlaced 1080i (field rate: 59.94 Hz) signal would be at 29.97 Hz (using the same bandwidth) or at 59.94 Hz (using twice the bandwidth); I have not heard of deinterlacers using the field rate as their output framerate, but I can certainly imagine it being possible.

It looks like 720p at 29.97 Hz is certainly part of the ATSC standard so I presume your ATSC Tuner would output it correctly if that was what was being received.

My guess is that the deinterlacing software/circuitry in your ATSC Tuner is to blame; maybe it only supports deinterlacing at 60 Hz field rate? Sounds as though Proscan may have cut corners somewhere.

I would return it if you can, or teardown if that is not possible and you are curious what the internals look like. If there is an FCC ID printed somewhere, you can usually look it up on its website and see pictures of the internals.

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I’m leaning towards software/firmware, as the decoder is adhering to spec, but the display output created by the SoC isn’t.

Unfortunately there is no FCC ID printed anywhere on the hardware. But if it’s using a common chip, I would like to know if a different firmware can be flashed onto it. The SoC has Thermal glue and a heatsink on it so I can’t remove it without compromising the heatsink, as I have no access to replacement thermal compound for the heatsink (not as simple as using thermal paste, this is thermal adhesive/glue)

However, there is a slight hint: CDA-MSD7802 reveals the PCB is made by Shenzhen HengKai. Proscan are not responsible for the hardware, only “slight” direction to firmware engineers for a splash screen logo.

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This is 100 percent accurate … Thank you Nyquist lol. They never will use the field rate what they can do is double the resulting rate but 2X deinterlacers are really only useful for high motion content like 120 hz lol. Everything you said is accurate

:100: percent correct. I think your diagnosis is spot on for the equipment and it doesn’t so much have to do with Bob deinterlacing

Yes exactly

Basically this

Most of this stuff is firmware anyways. Barring the hardware is fast enough which most is. Its about the firmware and the software processing and the DSP. There are so many products made in China. So much hardware that sometimes is stamped Taiwan but is shenzen and that’s simply a matter of supply chain. The magic is in the firmware

What type. Access should just be a matter of looking at its characteristics and sourcing it from Mauser or digikey. Therman adhesives are commonly used in engineering. We order them all the time.

Could you provide a link to the specification that you are mentioning and the specific parts of it you are referencing.

Also much like said above he is right ignore the spec and consider the real root source of the issue. I was reading through this and to me it seems you glossed over his break down of the issue in favor of your own? Could be wrong. Its a long thread.

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Well, I literally just found out what it was from that name alone without taking off the heatsink, It’s using a Mstar MSD7802. And it’s everywhere on the grey market on Alibaba.

Here’s a direct from Shenzhen listing of the exact same chip but sold on the grey market. Has detailed specs of the SoC and the description has my favorite furry movie out of Disney recently:

But, it looks like most of the firmware resources are in Chinese and Russian. The XDA Developers thread for Mstar only covers Android Mstar boxes. These run MIPS.

My next best option is to use an HDHomeRun and stream it to a Raspberry Pi. I don’t want to hog up a PC if I want to use a HDHomeRun setup.

For now though, unless someone that’s interested in Mstar MIPS firmware wants to chime in, I’m probably gonna get the Extron, because it’s needed to prevent image retention from bob deinterlace flickering.

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