Capturing RGB output from DVD/VCR combo

[Hackerpcs]

Is the capture card set to SECAM or PAL on the MESECAM image?

The default from the card, PAL_B

Does the color on the MESECAM capture look better if the capture card is set to SECAM (or MESECAM or similar if there is an option for it)? Setting the capture card SECAM should be the right option for capturing MESECAM unless the tape is actually PAL wrongly recorded in MESECAM mode which can happen.

PAL_B setting on capture card:


SECAM_B setting on capture card, no MESECAM option:


No difference

[nogginvid]

Couple of points here :

1. MESECAM is purely a VHS recording system not a broadcasting format. MESECAM (ME = Middle East ISTR) and French SECAM VHS VCRs will record and replay the same SECAM composite signals (they may have different tuners as they were sold in different markets). The difference between MESECAM and French SECAM VHS was purely to do with how the VHS VCR recorded the colour signal on the tape (MESECAM used a system similar to that used in PAL VCRs - which made multi standard VCRs that did PAL and MESECAM cheaper and easier, whereas French SECAM VCRs used FM division).

As a result there is no MESECAM capture format on capture cards - it's purely related to VHS VCRs as an 'on tape' format.

The composite output of a French SECAM VHS VCR and an MESECAM VHS VCR will be the same - composite SECAM. SECAM_B vs SECAM_G vs SECAM_L only really make sense at the RF tuner level - there is only one (*) flavour of SECAM at the composite level.

2. S-video doesn't really exist for SECAM ISTR - when S-VHS VCRs arrived they were standardised around using NTSC chroma in 525 (so there was no PAL-M S-video for Brazil) and PAL 4.43 in 625 (So there was no PAL-N or SECAM) on tape and on the S-video output connectors. As a result SECAM chroma is transcoded to PAL chroma for S-VHS recording, and the output of the S-Video VCR is usually PAL (not SECAM - unless there is a composite transcoder option to transcode back to SECAM). I don't think there was ever a formalised S-video standard that used SECAM chroma on the C-pins.

This means - I think - that S-VHS recordings made from SECAM composite sources are actually PAL (not French SECAM or MESECAM) on the tape.

3. Also some capture cards will auto-detect the chroma format - so will switch between PAL and SECAM decoding automatically if they detect a PAL or SECAM source (it depends on the composite / S-video decoder chipset being used and how its configured)


(*) SECAM actually did change formats slightly in the 80s in France in some cases. Originally SECAM used Vertical Blanking signals (the famous 'bottles') to synchronise the SECAM colour carriers in receivers, but this was changed to a line-based burst system (like PAL and NTSC) in the 80s in many cases, so that more of the blanking interval could be used for data like teletext and encryption data for scrambled channels etc.

[DB83]

^^ TBH I am having some difficulty in accepting everything you write.


We can all agree that Mesecam is not a broadcasting standard but a means of recording a Secam signal to VHS.


In the perfect world one would simply acquire a vcr capable of recording pure Secam signals. But the world is not, and has never been, perfect. So the Mesecam format was, if I read correctly, devised to record to tape but more closely to PAL than pure (French) Secam. Aka Secam_L.


Secam_B (as in Greece) is not Secam_L (as in France). Yet I have not found a source that distinguishes between the two. But they must be different else why have different names.


If the recording on the tape was pure Secam the OP could choose Secam_L as the source and have colour. I guess he tried and got B&W.


So Secam_B at capture level really is the same as choosing most of the PAL variants B/I/G. They are all the same since at the capture point there is no distinction. As he found out in the above samples. Much like I can choose PAL B/I/G and still see the same results for a PAL tape.


None of which answers the OP's Q.


But I think he is chasing his own tail here. Many believe that capturing pure uncompressed is the same 4:4:4 i.e. the same as pure RGB. I beg to differ. You are merely throwing bitrate at a subject with no ultimate visual rewards since your compressed/lossless capture is converted to RGB at the point of display regardless.

[nogginvid]

^^ TBH I am having some difficulty in accepting everything you write.

OK - I'm a former broadcast engineer - so have a bit of experience in this stuff. I've also done some develoment work with capture cards (albeit in a slightly unusual context)

We can all agree that Mesecam is not a broadcasting standard but a means of recording a Secam signal to VHS.

Yes - MESECAM is a SECAM VHS VCR recording method, as distinct to the system used in France to record SECAM on VHS. It uses heterodyning of the chroma subcarrier(s) like PAL and NTSC VHS does, whereas the French approach divides the SECAM FM subcarriers (unlike PAL and NTSC which uses QAM, SECAM uses FM) by 4 (I think) to create the colour under subcarrier.

This means the tapes recorded by the VCRs are different - but if you are using CVBS baseband (not modulated RF) as your input and output formats - the input and output formats will be the same - SECAM. At the baseband level (i.e. what you have on a SCART socket or an RCA phono) they are essentially identical.

In the perfect world one would simply acquire a vcr capable of recording pure Secam signals. But the world is not, and has never been, perfect. So the Mesecam format was, if I read correctly, devised to record to tape but more closely to PAL than pure (French) Secam. Aka Secam_L.

SECAM L is only relevant to SECAM when you are talking about the RF domain - SECAM L means RF System L carrying SECAM colour video (i.e. how the signal is broadcast / received by an antenna). It's relevant if your capture card has a built in RF tuner (just as things like NICAM are - and why PAL I and PAL BG, and SECAM BG are offered as different formats)

System L was only used in France (SECAM L added the colour to System L) - it uses positive video modulation and AM for the sound subcarrier at 6.5MHz offset.

SECAM B/G used the same RF system (System B or G) as PAL B/G and uses negative modulation and FM for the sound subcarrier at 5MHz offset.

The only difference between SECAM B/G and SECAM L is at the RF broadcast level - i.e. if you're using a capture card for RF reception (i.e. an RF / antenna output from a VCR)

If you are capturing baseband - i.e. SCART or RCA Phono - the signals are identical - and are also identical whether the VCR used MESECAM or the French SECAM VHS recording system.

Secam_B (as in Greece) is not Secam_L (as in France). Yet I have not found a source that distinguishes between the two. But they must be different else why have different names.

The only difference will be at the RF tuner level. SECAM B and G use RF System B and G, SECAM L uses RF System L.

If you feed baseband (via SCART or Phono) then they are identical.

If the recording on the tape was pure Secam the OP could choose Secam_L as the source and have colour. I guess he tried and got B&W.

IF the recording on tape is French SECAM and played back on a French SECAM deck then yes the output will be the same if the recording on tape is MESECAM and played back on an MESECAM deck AND captured at baseband.

If you play an MESECAM tape on a French VCR, or a French tape on an MESECAM VCR you get B&W.

What can be confusing is that you can - on some capture cards - get colour pictures for SECAM when you capture PAL or PAL when you capture SECAM - bceause the chroma decoder can run in auto mode. HOWEVER you still have a B/G, I, L option for the RF tuner bit - and these are often prefixed with PAL or SECAM...

[DB83]

^^ So what you are saying is if the OP recorded the tapes on scart/composite input MESECAM does not enter in to the mix since the recording is effectively SECAM.


But surely if that was so he could select SECAM on his vcr, as in Reply #20, and see colour. But that is not the case.


So one must assume that the recording input was at RF level and the tape holds MESECAM - much closer to PAL than SECAM. Then your last line also does not ring true. And it is the vcr that converts the output to PAL not to SECAM.

[oln]

Huh? Not sure what you mean?

He gets proper color from the LG when he selects MESECAM for the MESECAM tape, and for the PAL tape, PAL gives correct color, which makes sense. It also looks like the capture card is able to automatically switch between PAL and SECAM as noted. (B/G, I, L isn't relevant as noted, since OP is not capturing over the RF out, which would just give worse quality anyhow, so no point in doing that.)

It seems the LG can play back both PAL, MESECAM and french SECAM tapes, while the SVHS deck does not support either SECAM version. (Both probably also has NTSC on PAL TV playback but that's not relevant here.) There is no conversion to PAL going on on either (There are as noted some SVHS decks with SECAM<->PAL transcoders but neither of these VCRs have that.).

I echo my earlier suggestion of getting one of the noted dvd-recorder models to put in between VCR and capture card if OP wants to improve the quality from the LG, as those can stabilize wiggle and jitter and prevent the capture card from having to drop frames and cause audio desync etc, and may be able to decode the color a bit cleaner too. I'm 99% sure neither of these VCRs have RGB output for the VCR side as that would be very unusual, and the service manual for the LG didn't indicate any conversion circuitry. (Getting a SVHS VCR with MESECAM is of course also an option but as far as I know there are only a handful of rare models where the TBC and DNR stuff functions work with SECAM of any form.)

[nogginvid]

^^ So what you are saying is if the OP recorded the tapes on scart/composite input MESECAM does not enter in to the mix since the recording is effectively SECAM.

No - I'm saying the reverse of this. I'm saying that the only difference between MESECAM and the SECAM used in France is on the VHS tape and in the VCR itself. MESECAM is purely a function of VHS VCRs and VHS tapes. It's just how the two different VHS formats that can record SECAM record the SAME SECAM signal onto tape and replay it.

MESECAM was really designed (after French SECAM VHS had already been designed) to allow for PAL/SECAM VHS VCRs to be made more cheaply (this is useful in areas where you would expect to receive and watch PAL and SECAM) - as MESECAM allows the circuits used for PAL colour-under heterodyning to be used for SECAM heterodyning. French SECAM VHS recording requires a totally different technique which doesn't allow the same circuits to be used for PAL and SECAM recording - so PAL/French SECAM VHS multi standard decks required additional SECAM-only circuits (which added cost in the early days). In some VHS VCRs French SECAM recording/replay was on a separate little daughter board that was only installed in French VHS VCR variants ISTR.

Later VCRs will have been available that supported PAL, French SECAM and MESECAM VHS recording and replay once the circuit costs reduced.

An MESECAM VHS tape played back on an MESECAM VHS VCR will output SECAM via SCART/CVBS phono, a French SECAM VCR tape played back on a French SECAM VHS VCR will output the same SECAM format via SCART/CVBS phono.

SECAM L vs SECAM B/G is purely a function at the RF modulator and RF tuner level.

Because French VHS VCRs used French SECAM VHS recording on tape they will have SECAM L modulators and tuners (so will tune and output SECAM L - positive modulation, 6.5MHz AM audio) via their antenna RF sockets. SECAM B/G MESECAM VHS VCRs will have used MESECAM VHS recording and will have SECAM B/G modulators and tuners (so will tune and output SECAM B/G - negative modulation, 5MHz FM audio) via their antenna RF sockets. (A lot of MESECAM VHS VCRs will also have recorded and replayed PAL B/G and recorded this on VHS as PAL - which will replay on any PAL B/G, PAL I, or PAL D/K VHS VCR as 50Hz PAL recording is always the same on VHS)

So one must assume that the recording input was at RF level and the tape holds MESECAM - much closer to PAL than SECAM. Then your last line also does not ring true. And it is the vcr that converts the output to PAL not to SECAM.

Some VCRs may have had MESECAM->PAL transcoders in them to allow an MESECAM tape to be replayed and displayed on a PAL-only TV (this may be a menu setting).

Also - as I've said earlier - AIUI some capture cards will auto switch colour standard in some modes. My guess is that PAL B/G and SECAM B/G capture modes are effectively identical - and enable auto switching on the capture card, but SECAM L capture mode may force SECAM (as there is no PAL L format in use anywhere).

[oln]

MESECAM and NTSC Playback started getting integrated into VCR Video ICs in the late 90s from what I've seen. For example the Sanyo LA71750EM used in a lot of the late-model 20x0s VCRs like the LG here, integrating Y and C processing for PAL, MESECAM, NTSC 4.43, PAL60, Head amp, delay lines, linear audio and some input switching all in one IC (there is also a multi-system variant with NTSC 3.58 support that has the same pinout). The equivialent NTSC variant is simpler as it only does NTSC. Don't think french SECAM ever was put in them as standard, but when you look at service manuals on e.g the LG the PCB is designed so that there is a spot for a SECAM IC to be put in for models sold in markets where it had some use, and the video IC can be switched via serial control to send the head amp signal out to the SECAM IC for processing.