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ADV7403 ADV7842 and ADV7850 chips

I am about to start a composite and s-video signal digitization project. Before i get started i need to establish which of your chips to use. I may as well start with what ever your current chip is as I may have been reading old internet webpages.

I have been looking keenly at your ADV7403 chip. Can you tell me whether this has been updated by your ADV7842 and ADV7850 chips and are there even any later chips than these? I could have easily missed something on your website.

Outputs required are digital(s-pdif)  for PC card capture and HDMI for the TV.  I will also require the 3D comb filter and TBC facilities mentioned for these chips in your datasheets. I will also require stereo inputs for the HDMI TV output.



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  • FormerMember
in reply to RagTag +1 verified

Audio CODECs can be found here

CODECs come with output DACs but you don't have to connect or use them them.  The key you are looking for is I2S bus…

  • FormerMember
    0 FormerMember

The ADV7842 has an input HDMI port and the ADV7850 has both input and output HDMI ports.  The analog sections are very similar. Both have 3D comb and TBC.  TBC was used to correct issues with old VCRs so I'd be surprised if you need it for modern systems.

The ADV7403 does not handle HDMI directly.  It only has a digital input port, not HDMI decoding.

If you need HDIM input and output plus analog decoding plus audio insertion I'd look at the ADV7850 single chip solution.  The ADV7842 is great where you need HDMI input and analog decoding feeding an FPGA or a ADV7511.  Note  these chip only handle HDMI 2.0 spec.  Do you need to handle HDMI 2.1?

Also keep in mind you will need to be an HDMI and HDCP adopter to use these chips with HDCP keys.

If you can include a list of supported inputs and outputs with formats required we can point you to a possible solution. 

  • Thank you very much for your informative reply. What i need to do first is to get the chips sorted out.

    input signals

    I have 2 input analogue Video signals to process:-

         1) composite (CVBS) from a laserdisc player
           1.1) Hence the need for an excellent comb filter to split this composite signal into its S-Video Y & C signals.

         2) S-video signal from VHS players
            2.1) And from the Lasedisc Y&C signal just mentioned
            2.2) VHS players - Hence the need for a TBC.

    Output signals

     I need 2 output signals:-

         1) Digital output signal for input into a computer PC capture card.
         2) HDMI output signal for input into a TV
            2.1) This will also need stereo input sockets to take the audio signal from the 2 input sources above.  

    What Chips do i need?

    How does the above translate into chips? And this is where i need your help. Can you sort me out here.    

    first possibility. Have 2 seperate chips in use on 2 seperate boards:-

         1) ADV7842 to take the input sources listed above and create a digital output signal for input into a computer PC card .
         2) ADV7850 to take the input sources listed above and create an HDMI signal for input into a TV.

    second possibility. Have 2 connected chips available:-

         1) ADV7842 to take the input sources listed above and create a digital output  for input to a PC card and ADV7511
         2) ADV7511 to take the digital output from the ADV7842
            2.1) to create the HDMI output signal for input into a TV.       

    I have a problem with the ADV7511 - its datasheet does not show an HDMI output connection. Can you update me on this.

    HDMI 2.0 will do the job very nicely.

    Hope the above makes sense. If i have anything wrong then please correct me on it.


  • FormerMember
    0 FormerMember in reply to RagTag

    Your option 2 is the way to go, ADV7842 -> ADV7511, Digital capture.

    Digital capture card is not very clear, does it capture CMOS digital bus or something else.  Normally PC capture cards have analog or HDMI inputs, not a digital bus.  Need a bit more architectural information here.

    The EVAL-ADV7842-7511 show you how to implement that solution.  Check out these links

    They'll show you how to get started with the ADV7842-7511 .

    You will also need an audio to I2S converter to inject the audio into the ADV7511 I2S port.

    The ADV7511 has a TMDS output which is the HDMI output.  Check the reference schematic to see how it's done.

    The ADV7842 also has an HDMI input which you could use as a normal input port, maybe as a test input from a PC.

    Other chips like the ADV7181D will decode your sources but don't have the TBC feature.

  • Thank you very much for the reply which has given me  a lot to digest. There are some areas i didn't know existed.  

    Thanks for raisng the PC card question.  I need to look further into the PC capture card end of the business. This is not something i have done as yet, I

    just assumed that there would be PC Card that takes digital input. Whether I expected your digitizer chip  to combine the audio signal  into the digital

    signal or Whether i was expecting th PC card to take the audio signal, digitise it and mix it with the digital signal, i just don't know at this stage.  I

    know i have in mind that the PC card would capture RAW video footage into a .DV file, ie no codecs at this stage. I know this would produce large files, but

    modern PCs should easily cope with this. Maybe i have a lot to learn. As for audio, i would like to be able to capture, whatever the method, at 96htz/24bit

    at least.  

    In the meantime can you answer a question on TBCs. This time about the ADV7842 TBC as TBCs are important for VHS cassette playback.

    Does the ADV7852 TBC function as as internal or external TBC?

    On VHS players the internal TBC cleans up TV display artefacts, all squiggles and other aberrations that often show on the TV.

    The external TBC is purely for the PC Capture card and is neccessary to replace  the current timestamps on the analogue signal with precise timestamps required by the PC capture card  and also to release the signal at an even rate for the PC capture card. Without an external TBC the PC capture card may very well fail to capture the video.

    These are my interpretations of the large quantity of notes I have on TBCs, i hope my interpretations are correct.

    Full frame TBCs are better than line ones.  

    My own tests have shown however, that with the  VHS internal TBC switched on, that LCD TV picture quality is pleasantly improved with an external TBC between the VHS player and LCD TV.  That is, the LCD TV likes a decent, well sorted signal.  



  • FormerMember
    0 FormerMember in reply to RagTag

    1) ADV7842 and ADV7850 have internal TBC and use external SDRAM for temporary frame storage.

    2) TVs and HDMI sinks like stable time based video.  VCR has some time jitter in the frame rate.  TBCs (Time Base Correction) captures the input, stores it in the SDRAM frame buffer and outputs at a stable frame rate.  Full frame TCBs are better.

    3) I don't know of any digital bus PC capture cards.  All I've seen have analog or HDMI inputs.  (Capturing a  video digital bus over a cable would be painful.)

    4) Another option is run every thing through the 7842 so the TBC can be used then have 2 ADV7511s, one going to the TV and the other going to the PC capture card.

    5) My next suggestion is draw up a simple diagram showing the video and audio signal flow paths.  From this you can determine the chips to use and define various use cases.

    Right now it seems to make more sense to run everything into the ADV7842, let it do the TBC, then have 2 ADV7511's, one sent to the PC, the other goes to the TV directly.

    Of course audio would need to buffered and split the same way.

    When you get to this point you can get an EVAL-ADV7842-7511P board to test things out.  Only ~$200.

  • It sounds like the TBC on the ADV7842 is acting like an external TBC and correcting the timestamps (ie jitter) rather than acting like  the internal TBCs on VHS players such as the American Panasonic AG-1970 and AG-1980 VHS players which correct the picture.

    One last question on the ADV7842 TBC.  How does the ADV7842 TBC operate:-

    1) does use an input a digital signal that it performs corrections on? Does it output a digital signal?

    2) or does it work in the more traditional VHS TBC sense of converting the Analogue signal  to a digital signal, performing the corrections on the digital signal and then converting the corrected digital signal back to an analogue signal for output (A-D-A).

    CVBS(composite) input signal on the ADV7842 -  are the 2D and 3D comb filters applied to this signal before or after the signal is digitised?.

    After what you have said i think I am really going to have to look into PC capture cards. It could alter what i am thinking about entirely.

    I like what you say about the price of the evaluation board.   

  • FormerMember
    0 FormerMember in reply to RagTag

    I might not understand your definition of internal and external.  It really doesn't matter as long as you get the results you are looking for.

    Check out the detailed functional block diagram.  The ADV7842 digitizes the analog input, runs it through a series of  processing modules and outputs digital data.  These modules include 3D comb and TBC.  It uses the external SDRAM for frame and line storage for the TBC and 3D comb functions.

    The ADV7842 has two video path depending on the input.  The SDP handles CVBS video while the CP handles other higher formats, normally progressive.

  • I think my questions are to getting to detailed so lets get back to the evalution board.

    I am just trying to get some idea of how the ADV7842 works and the order of processing. Things are not so visible on a chip as they are with hardware.  

    hope these questions are a lot easier. I have 10 questions, here is the first 5 and then maybe down to biz:-

        1) When an S-video signal is input into the evaluation board are the comb filters used?

        2) can the TBC be turned of if required/ preferred.
        3)  How ar the settings changed. All the setting and controls eg output bit rate selection, 4.2.2 or 4.4.4, appear to be controlled by jumper switches. Can these be bypassed/ overidden  by switches on the box containing the evaluation board to give easier selection facilities or does the lid have to come off the box to change the jumper switches.

        4) MAcrovision 1,2 and 3, CGMSa - is there any contact points to which LED lights can be attached, to show which level of macrovision is present, if any.

        5) PAL/ NTSC/Secam - is there any contact points to attach LED lights to show which of these formats is in use.

  • Lets try and clear up interenal and external, we both have different meanings for these words.  Nothing for you to answer here

    Internal and external TBCs are both associated with VHS players and perform different functions but to do their correction they both convert the analogue (composite or s-video) from analogue too digital and then back to to analogue (A-D-A). Corrections are carried out on the intermediate digital signal. If both of these types of TBCs are in the system then thats 2 lots of conversions.  Both the A->D and the D->A conversations cause some loss to the picture quality  and the internal TBC is often accused of softening the TV picture.  

    INternal TBC
    An internal TBC comes as part of the VHS player, that is, it is part of, and internal to, the product. Hence "internal". There is a switch on the control panel to turn it on or off as required. It was also associated with a DNR which might have its own switch or is combined with the TBC. As i stated the  purpose of the internal TBC was to clean  up the analogue signal  of artefacts caused by the vhs player and or the vhs cassette before it was transmitted to the TV.

    External tbc.
    The external TBC is a seperate item to the VHS player and sold seperately.  It is outside the VHS player, hence "external". Analogue video cables from the VHS player  are routed to it and its ouput analogue video cables are routed to a PC capture card. Its sole purpose is to tidy up the analogue signal (composite and s-video) to remove jitter and produce a nice even signal for input PC capture cards are that are more demanding on the presision of the signal than a TV is.

    Note that the DNR mentioned may also perform its own A-D-A conversion sequence on the analogue signal.

    These A-D-A conversions suited the equipment of 20 years ago but now are just archaic. Once the signal is in the digital domain is should just stay there, thats my opinion. Modern equipment can cope with it and each conversion creates some loss to the picture quality.

    What i was trying to find out was how much the ADV7842 TBC can dispense with these conversions and the  A-D-A sequence of conversions, and whether it just takes a digital signal produced elswhere in the ADV7842, corrects it, and outputs the digital signal for processing elsewhere on the ADV7842. That is, its dispensed with the now uneccessary D->A conversion and subsequent A->D by the LCD TV which should help TV picture quality.   

    From what you have said the ADV7842 TBC performs the functions of, in the sense that i am using the word "external",  an external TBC. That is, it cleans up the  overall signal for  the PC capture card but does not clean up the sqiggles and other artefacts that can appear on a TV.  This means that the  VHS players internal TBC ( + DNR) will still have to used to do this job.  

    I am beginning to sound like an expert which i am not.

    OK, enough of that and on with the biz    

  • FormerMember
    0 FormerMember in reply to RagTag

    As you stated, every A-D and D-A introduces a bit of loss.  The fewer domain conversions you have the better off you are.

    The first thing the ADV7842 does to analog inputs is digitize them with a 12-bit ADC.  From that point onward all processing is done int 12-bits in the digital domain. The  processing modules are basically all in series with each module having a bypass path so each module can be included/excluded into the path as needed.  This includes the comb filters, TBC, peaking, color space conversion, output format, de-interlacing....

    Please look at the detailed feature diagram in the data sheet

    From your explanation the ADV7842 TBC would be an external TBC to the VCR and the final TBC in the system.

    All these controls are controlled by register accessed over an I2C interface.  We provide scripts for various input/output formats configurations.  AvesBlue is a tool to access the evaluation board over a serial port, displays all the registers and allows you to run scripts and toggle the control registers.  Download it and try it out.  You can use the NULL driver to see the windows in action if you don't have an eval board.

    Note the EVAL-ADV7842-7511P has two modes of operation, one where AvesBlue and scripts control everything and one where the embedded code in the BlackFin controls chip configuration as inputs and outputs are plugged in/out.

    The ADV7842 does detect macrovision.

    I hope this answers some of your questions

  • Reply
    • FormerMember
      0 FormerMember
    in reply to RagTag

    As you stated, every A-D and D-A introduces a bit of loss.  The fewer domain conversions you have the better off you are.

    The first thing the ADV7842 does to analog inputs is digitize them with a 12-bit ADC.  From that point onward all processing is done int 12-bits in the digital domain. The  processing modules are basically all in series with each module having a bypass path so each module can be included/excluded into the path as needed.  This includes the comb filters, TBC, peaking, color space conversion, output format, de-interlacing....

    Please look at the detailed feature diagram in the data sheet

    From your explanation the ADV7842 TBC would be an external TBC to the VCR and the final TBC in the system.

    All these controls are controlled by register accessed over an I2C interface.  We provide scripts for various input/output formats configurations.  AvesBlue is a tool to access the evaluation board over a serial port, displays all the registers and allows you to run scripts and toggle the control registers.  Download it and try it out.  You can use the NULL driver to see the windows in action if you don't have an eval board.

    Note the EVAL-ADV7842-7511P has two modes of operation, one where AvesBlue and scripts control everything and one where the embedded code in the BlackFin controls chip configuration as inputs and outputs are plugged in/out.

    The ADV7842 does detect macrovision.

    I hope this answers some of your questions

    Children in reply to RagTag

    6) The ADC sampling rate matches the input format rate.  For example if the input is CVBS then the sampling rate will be 27MHz.  If it's 1080p60, then it's 148.5MHz

    7) The ADV7842 is only designed for one specific DDR, K4H561638J.  Bandwidth through the memory is not an issue since it's only used for CVBS video streams. It's a 256Mb, part

    8) It's U22 in the picture.  Implementation is shown on the schematic

    9) Yes, you will need an analog to I2S converter connected to the ADV7511.  One of ADI's main product lines are audio encoders/decoders.  I am not as familiar with ADI audio lineup but when the time comes we can definitely help you here.  I've used the ADAU1761 on my last design and it worked well.

    10) If you look at page 8 on the schematic you will see the I2S bus connecting to the ADV7511.  These pins come out to the header J4

    As far as indicator lights go, When the ADV7842 powers up it must configured by a uProcessor.  On the eval board we use a BF524.  Almost any uProcessor can be used as long as it can drive the I2C bus and has enough memory to hold scripts.  The uProcessor can monitor 7842 registers and set indicators as needed.

    With the eval-adv7842-7511p, AvesBlue has a probe function that can simulate indicators you are looking for.

    Hope this helps

  • You have brought my attention to the fact that I really need to get to grips with the computer capture end of the conversion system.  

    I do want to capture raw video footage from composite and s-video input.   

    Can the ADV7842 (by itself - no ADV7511 connected)  be switched between  "12-bit 4:4:4 and 10-/8-bit 4:2:2 DDR pixel output" just as the ADV7403 can?.

    I would really like to capture video at 12bit 4.4.4 on the computer. The method of capture on the computer has to be sorted out as yet.


  • FormerMember
    0 FormerMember in reply to RagTag

    The ADV7842 can easily switch between output formats.  In UG-214, user guide check output appendix D.

    I suggest staying with SDR formats.  The pixel rate is the same between DDR and SDR, it's just that the LLC is running at 1/2 the pixel rate.  DDR is harder to capture and intended mostly for FPGA interfaces which have hardware specific DDR receivers.

    As far as ranking pixel bus formats from best to worst it goes

    4:4:4 -> 4:2:2 -> 4:2:0

    4:4:4 needs 3 8/10/12 bit busses

    4:2:2 needs 2 8/10/12 bit busses

    4:2:2 extrapolates color data between pixels so you lose some of the original data.  Compression technique to lower data rate/bus widths.

    As far as bus widths

    3 x 8 bits provide ~16 million colors

    3 x 10 bits provide ~1 billion colors

    3 x 12 bits provide ~69 billion colors

    As far as color space goes RGB is better then YCbCr regardless of bus width.

    I've seen some studies that show humans can only differentiate up to ~10 million colors. I've never understood why we need more then 24 bit color.  Personal opinion.  (Is it a marketing plus to say 'we do deep color')  The only reason I can think of to use deep color is that any artifacts created by post processing is covered up in the lowest bits and won't be seen by the eye.  There's also a spec for 48-bit color.

    I'd like to know why your product needs deep color.  What do you gain from it?

    The HDMI (ADV7511) can carry all the formats mentioned above up to 4:4:4 36 bit bus.

    As you sort through all your video issues may I suggest the video bible I use, Video Demystified.  Available as   pdf or paper book from amazon.  

    I hope this helps,  any more question I'll be here

  • Are you saying that the evaluation board can send a 12 bit (or is it 36 bit) 4.4.4 RGB video signal at maximum sampling rate (27mhz you said for Composite, s-video) through the ADV7511 hdmi output connection to the computer? This should not involve any codecs or compression as  i do not want any. This would provide a means to an end as it would solve my PC capture card  requirement as recent investigations have, as you said, shown most capture cards these days have and HDMI connections, they do not have the old analogue connections or even digital connections. Providing the capture card does not mess with the signal and just allows the signal to be written asit  is to a disk drive file that would keep me happy. That would take care of the hard work. Does this require the use of HDCP keys? Hopefully not, but HDCP keys will still be necessary TV output. I do not want to burden the process with license protection.  

    I have looked into PC software for capturing the digital signal to the computer and so far Cyberlink Power Director and NCHsoftware sound promising. What do you use?.

    As for deep colour i have not even considered that.

    My intention is to lay down binary ones and zeroes as good as they can be from the input sources and take it from there. Cleanup and editting processes will  follow. I don't see that reducing the amount of chroma with 4.2.2 is necessary with the power of computers these days. And why loose data on capture? That  can be done later if necessary.  But its nice as a lower spec option if i choose to use it. So 4.4.4 (RGB) for capture.  

    For  computer capture I had been thinking along the lines of using the ADV7842 outputs somehow, converting them to a .DV-dif file/signal somehow and sending  them to the PC  using A USB connection??? This is all speculative of course. Software on the PC would then capture this signal and write it to disk.   

    Can you clarify what you said about DDR as this has thrown me somewhat. Where does it fit into what has been said?

    Thanks for the mention of the book. I may read it but i have the feeling that it is one of those items that will take me too deeply into the theory of the  conversion subject which i see as cables, and electronics at the moment.


  • FormerMember
    0 FormerMember in reply to RagTag

    1) About HDCP keys.  You are only require to handle HDCP keys if the source requires them.  DVRs and set top boxes implement HDCP because their video sources require the license for copy protection.  HDCP only works over HDMI connections.  Analog sources don't have any HDCP so no need to worry about them.  The ADV7842KBCZ-5P has no keys so its not a problem, can't break the copy right infrigement..  

    2) I don't use PC capture cards.  I use HDMI analyzers to capture images and a lot more information.  Many of the current capture cards are USB dongles connected over USB 3.  They come with analog or HDMI inputs.  The old fashion capture card that plugs directly into the PC backplane bus are not that common anymore.  Regardless these dongles load the video stream into main memory as a raw file or probably a converted file like DV.  The software packages you mentioned either taps directly into the stream or works with saved files.  They are basically video editors.

    3) All the 7842 can do is convert the video input (either HDMI or analog) into a 24-bit stream.  How it gets into the PC is another matter.  This is what the video to USB dongles do.  So are you designing a USB dongle?

    4) 12-bits per color plane is deep color,  RGB444 would have 3 color planes making a 36-bit bus.

    5) Somewhere above you said you wanted to use 24-bit DDR.  I was just saying SDR is easier to work with.

    6) The first several chapters of the book will give you information on exactly what color space are and what 444,422 mean and how to work with BT601 and BT656.  BT601 and BT656 are an 8-bit bus format for CVBS formats.

    Going back to the start of this thread you were looking to use the 7842 for it's TBC and 3D comb features for VCR outputs and now wanting this stream in RGB444 format.  The real issue is how are you going to get the RGB444 stream into the PC for editing by those software tools.  I don't know of any RGB444 to USB bridge implements.

    It could be done but probably needs FPGA solutions the plug directly into the PCI bus of the PC or as a dongle adapter running over USB.  That's lots of work unless you can find something off the shelf.

    It might help if you drew up a diagram of where you want the video stream to flow and in what format. Include lots of details that we can throw darts at.

    If I were to do this I'd build my system like this

    analog inputs -->

        ADV7842 for TBC and 3D comb, 36 bit digital output -->

            ADV7511 to convert to a HDMI stream -->

                HDMI to USB dongle -->

                    Video editing software.

  • USB Dongle - No, i am not building a USB dongle. Thats way out of my league. So can the ADV7511 HDMI output be used to transfer an output signal to a PC capture card? There are still quite a few PC PCIe Capture cards out there with HDMI input connections. Black Magic are still making them.  As i said, that  would solve my capture problem.  I am just trying to go with whats available on the markets.   

    HDCP keys - do i still need a 7511  with HDCP keys to display the now converted composite and s-video input signals on an lCD/ LED TV?

    Capture software - the packages mentioned have capture facilities which are required for eg webcams and hopefully PC capture cards. I need to investigate  these packages more.  If they will capture without applying codecs or compression then that is what i want.  
    DDR - Does DDR refer to double data rate  or the DDR memory on board the 7842/7511 evaluation board? If the 12 bit colour plane  you mention is SDR then that  is what i want, not DDR.  I am still not sure what DDR means here.

    CVBS and S-video capture - can the 7842 convert these inputs to 36 bit RGB 4.4.4 digital output or is the conversion limited to 8 bit.

    Workflow - more or less the same as what you laid out
        analog inputs -->

        ADV7842 for TBC and 3D comb, 36 bit  RGB 4.4.4 digital output -->

            ADV7511 to convert to a HDMI stream -->

                HDMI  to
                    1)  PC capture card -->

                    Video capturing software.
                    2) LCD/LED TV

    WIll the ADV7511 output the full 36 bit RGB 4.4.4 digital stream as is, or will it convert or compress it in some way?  Does converting to an HDMI stream involve compression?  

    Will the  36 bit RGB 4.4.4 digital stream display, via an HDMI cable,  on an LCD/LED TV?    


    Perhaps i am over egging the pudding. I usually do. All that is required is to write the 36 bit RGB 4.4.4 digital stream to a USB stick. How about using the USB port on your evaluation board? Favourite for the USB drive would be a 1TB PCIe drive card, M.2,  in a USB/ PCIe caddy, both are are available on Amazon. The Caddy has a PCIe to USB bridge at USB 3.2 gen 2 whatever it is, anyway, 10 Gb/s, far faster than any USB stick. So thats the terrific speed of a first class USB connection, the blazing speed of of a PCIe drive  plus the capacity of the PCIe drive, 1TB!  That would really do the job! Then, after capture,  simply transfer the PCIe drive and caddy to a USB port on the computer for further processing. PC capture card dispensed with!  Evaluation board now purely for TV display!   

    Hope thas useful  

  • FormerMember
    0 FormerMember in reply to RagTag

    1) The ADV7511 outputs HDMI so it will work with either PC capture cards or TV's

    2) You do not need HDCP keys to output to TVs.  HDCP keys are only requested from TVs if the source requests them and analog sources will never request them.  So no key problems.  The ADV7511 comes with keys but since the 7511 is only a transmitter, the powers to be don't care if you transmit encrypted or plaintext.  You can turn it on and off as needed.  Now the powers to be do care about receivers with keys since with them you can violate copyright rules.  Bottom line is TVs don't care, they'll display plaintext video just fine.

    3) DDR == Dual Data Rate, SDR == Single Data Rate.  Basically SDR present new data on only a rising or falling clock edge while DDR presents new data on both clock edges.

    4) Capture cards can replace the dongle.  I just though a dongle would be more more convenient then opening up a PC to install a PCI card.  (Hard to do on a laptop also)

    5) Basically the ADV7511 is just a parallel to serial converter.  For video streams compression only occurs when you do 444 to 422 conversion, the pixel colors are compressed from 8 bytes down to 4 bytes.  This conversion can be disabled.

    6) RGB444 over HDMI will display on TVs.  

    7) The USB port on the eval is a control port only and has been deprecated.  Now we only recommend using the serial port for control.  (Software issues).  It cannot carry video.

    8) BIG IDEA.  The hard part is writing a 36 bit stream to a memory card.  This is what the capture cards/dongle do.  Remember video is a continuous data stream while USB to memory transfers are block transfers.  How do you convert a continuous streams into block transfers.

    I think I addressed most of the questions.  

  • AnNother great answer. It's all coming together at last! It looks like i can get everything i want out of your evaluation board.

    I think thats about all on the video side.

    I wish to start a new series of AUDIO Q/A as this video one is getting long 

    Big idea  - take 2

    I appreciate what you said about writing a 36 bit stream program but applications like nchsoftware and Cyberlink Power Director do it so the question is how. The real problem here is not to let the writing to disk of the recorded input stream  interrupt the recording of the input stream so the write to disk function would have  to be a lot faster than the recording of the input stream.

    This takes me back to my programming days where, when running the programs i had written, they would be given a number of input buffers by the OS which would be filled and controlled by the OS.  As you said, this is a block driven process. The applications i mentioned must be using a similar technique of having a number  of input buffers which the application will have  to empty a lot faster than the input stream can fill them up.

    How could this be done?

    This is a conceptual solution.

    Lets start with the USB PCIe caddy i mentioned at 10Gb/s with a USB 3.2 gen 2 (or whtever it is) on the PCB  that can write at something approaching 10Gb/s.         

    The program to record and write the input stream:-

        1) has, lets says, 6 buffers at, lets say, 32KB.

        2) the buffers are in ram (the evaluation board DDR chip or an upgraded or dedicated  memory chip)

        3) When  a 32KB buffer is full the program moves onto the next buffer and the full buffer is written to disk (the PCIe drive i have just mentioned). Each full buffer has now become a "block"
        4) The  32KB of a full buffer could be written to PCie disk all at once or, if such a large write to PCIe would interupt the recording of the input stream, at smaller amounts, lets say 4KB, that could make use of microsecond gaps when the input stream is not being recorded to a buffer.

        5) the program cycles around these 6 buffers sequentially.

        6) Making sure the buffers are empty before they are required again is the clever bit.  
    An alternative is to write the input stream straight to PCIe card which would save a lot of messing around with buffers and memory and, providing the write  to PCIe is faster than the rate at which the input stream is arriving, would be a very neat solution.

    How about a Thunderbolt 4 connection straight to a PCIe card, ie miss out USB altogether!  

    Whats recorded on the PCIe card is a single file, lets say 300GB of yuk.

    On completion of the recording the PCIe caddy is transferred to a computer where there is a program that can format the 300GB of yuk into a raw file of, lets say, 80 byte dif blocks (80bytes seems a bit small to me).  The point about the raw file is that it can now be be editted by an appliction that can process raw files.

    This is not a bad system with all parts of the process, capture ->  format -> edit, split up into separate jobs. The capture part, which is the difficult and partly unknown part of the process, has been well and truly isolated from the rest which can now proceed at a more leisurely speed.  

    OK, its a thought

  • FormerMember
    0 FormerMember in reply to RagTag

    All PC capture cards (let's use pexhdcap60l2 as an example) will have some sort of frame buffers that they ping-pong back and forth to capture video streams using an ASIC or FPGA.   Then it normally compresses the video stream into H264 format and then sends the packets over the PCIe interface to the main memory.

    I believe H264 can be set as lossless.  Compression still happens, you just don't lose any raw data.  Once in main memory you can decompress it back to RGB.  I just don't know of any video RGB file formats.  The video editors only work with files in main memory, not directly with the capture card.  It may look like editors work directly with the capture card however the the video is just moved in smaller blocks then an entire file.  (Something similar to pipes)

    video --> capture --> compression(H264) --> PCIe --> main memory --> video editor

    You can't sent video directly to main memory over PCIe.  PCIe is a bus and must be shared so PCIe packets must be created and sent only when the bus is free.  This is what the PCI interfaces do.

    Thunderbolt is similar to USB except its specs include video transmission.  All video is packetized. (Uses the same USB-C connector)

    On another note, originally we started with digitizing S-Video VCR outputs.  The S-video output my only use an 8-bit DAC.  You don't need 12-bit of data to capture an 8-bit source.  Nothing is gained by the extra 4-bits, it's just noise at best.

    If you want to start talking about audio then please start another thread, this one is kind of long already and really dedicated to video.