How and why are dropped frames "bad"?

[plehoediv]

Hi,

I read the thread on why you might get dropped frames when capturing. However, it did not mention why dropped frames are an issue, and from what I read on here, they are. But why? I always figured that if the video and audio are on the same track, they are on the same frame, right? So, if they are, you would also lose the audio, together with the video, thus not having any sync issues at the end.
As a matter of fact. I notice ZERO sync issues with as many as 12 frames dropped, on a 3h tape. And let me tell you, I am super sensitive to video/audio sync issues.

Thanks.

EDIT: I forgot to mention that most of the the dropped frames occur when the tape "transitions" from one recording to another. I am not sure how to call it, but you know what I mean. When one recording ends, then there is static, and then there is another recording following.

P.S. Just for fun I asked ChatGPT, "Are video and audio recorded separately on a vhs tape? And here is the answer:

On a VHS (Video Home System) tape, the video and audio are not recorded separately. Instead, they are recorded together on the same tape in an analog format. The VHS format combines both the video and audio signals onto a single magnetic tape.

When you play a VHS tape, the tape passes over a rotating video head and an audio head. The video head reads the video signal from the tape, which consists of a series of horizontal lines that form the moving images. The audio head reads the audio signal, which corresponds to the sound associated with the video.

During the recording process, the video and audio signals are captured simultaneously by the recording device, such as a VCR (Video Cassette Recorder). The signals are then encoded and recorded onto the VHS tape as a single composite signal.

When you play back the VHS tape, the video and audio signals are read from the tape together and sent to your television or audio system for decoding and playback. The television or VCR separates the video and audio signals and processes them accordingly to display the video and play the audio.

[davexnet]

Well the HiFi audio and video are recorded by two separate heads on the drum, so in that sense it's separate.

When a frame is dropped it causes the previous frame to be repeated, leading to a visible stutter when the file is played back

[Skiller]

Dropped and/or inserted frames (not the same thing, btw.) indicate there is a problem, unless the number is very, very low. (I would ignore anything below 10 drops/inserts per hour of capture.)
It may indicate the sychronization pulses of the incoming analog video signal are too wonky to digitize a frame properly, or there may be an issue on the PC side of things, while writing the data to the HDD (interfering background tasks for example). And, of course, they may indicate audio sync issues.

Audio and video are handled independently inside the VCR, although the VCR cannot affect sync because it simply has no means of doing so.

[plehoediv]

Well the HiFi audio and video are recorded by two separate heads on the drum, so in that sense it's separate.

When a frame is dropped it causes the previous frame to be repeated, leading to a visible stutter when the file is played back

I am not going to argue with you if it is separate or not, because I am not an expert, and I can only go by what I read. However, I still don't see why a repeated frame would be an issue? Fine, you see a stutter for a split second (25th of a second, in my case, I guess) but who cares, if anyone even notices. Besides, if the dropped frame is repeated by the previous one, why would there be a sync issue?

And like I said, I have no sync issues after 25 dropped frames and 3h later. Explain that.

Thanks.

[plehoediv]

Dropped and/or inserted frames (not the same thing, btw.) indicate there is a problem, unless the number is very, very low. (I would ignore anything below 10 drops/inserts per hour of capture.)

Glad to hear that because my "OCD" (not official, ha ha) is making me re-capture tapes that have 1 or 2 dropped frames over the span of 3hours.

It may indicate the sychronization pulses of the incoming analog video signal are too wonky to digitize a frame properly,

That could be the problem. From what I remember, I had ZERO dropped frames when using my Panasonic EX95V. Now I am using my Blaupunkt RTV936 and I have dropped frames. That sucks because the EX95V had tracking issues. So it seemed.

or there may be an issue on the PC side of things, while writing the data to the HDD (interfering background tasks for example). And, of course, they may indicate audio sync issues.

I did not change anything on my PC so I think it must be the RTV936 that is doing this!?

Audio and video are handled independently inside the VCR, although the VCR cannot affect sync because it simply has no means of doing so.

Ok. Thanks.

[davexnet]

Dropped frames don't cause a sync problems because a duplicate is inserted, thus sync is maintained

[dellsam34]

Unless the settings call for it, You can mess up the capture software setting to not insert frames in case they are missing, therfore there will be audio drift, For the OP's case I would say a combination of wrong capture software settings and lack of signal stabilization by a way of TBC.

[plehoediv]

Dropped frames don't cause a sync problems because a duplicate is inserted, thus sync is maintained

Not only does it make sense, but I can literally see no sync issues. . So, in other words: If a "stutter" doesn't bother you, or you don't even see it (the stutter), dropped frames are not an issue. Right?
See, originally, I thought they (dropped frames) would "shift" something around and cause an issue, somewhere, down the line, like the Butterfly effect. I mean, if something is dropped, something else has to give, right? But I guess that is not the case since the frame is simply "replaced".

BAM! Thanks. No need for me to re-capture 10 tapes again because here and there is a frame missing.

[plehoediv]

Unless the settings call for it, You can mess up the capture software setting to not insert frames in case they are missing, therfore there will be audio drift, For the OP's case I would say a combination of wrong capture software settings and lack of signal stabilization by a way of TBC.

I use Scenalyzer and from what I remember, I did not change any settings. The signal goes from my VCR (no TBC) to my Camcorder TRV820e with TBC and from there to my PC. But again, if I have no sync issues, I have no issues, other than dropped frames, which are not an issue. .

Thanks.

P.S. I am glad this turns out to not be an issue because I wanted to get my good old Dell PowerEdge T620 Server going again, so I can, yet again, capture all tapes that had dropped frames. Turns out I screwed up the order of my 6 hard drives AND I have memory issues... glad I do not have to fix that because I have no idea how to setup RAID, ha ha.

[dellsam34]

I though you are capturing analog signal and have sync issues, So you're just ingesting the converted signal to DV into computer, So what's your problem then?
That VCR explanation you were given is wrong, or at least it was dumbed down to a point it became wrong, Audio and video are two separate things before entering the VCR, when they are recorded on tape and when they are played back from tape, and when going in to TV on a separate cables and processed on different circuit boards, the only relationship between audio and video is just timing. On broadcast TV in the other hand it's a different strory but that is unrelated to VCR.

[lollo]

I use Scenalyzer and from what I remember, I did not change any settings. The signal goes from my VCR (no TBC) to my Camcorder TRV820e with TBC and from there to my PC.

If you use a DV Converter to digitize the analog signal, the "classic" definition of inserted/dropped frames does not apply, and you have little control of what happens during the Analog to DV conversion.

The digital signal captured may show dropped frames while the stream is transferred to the PC via SCLive, which may happen for reasons related to the DV converter and/or the PC. They are somehow different from the inserted/dropped frames inherent to the Analog to Digital conversion. A check with AVPS DV Analyzer on the captured DV file is useful to check potential issues.

[plehoediv]

I though you are capturing analog signal and have sync issues, So you're just ingesting the converted signal to DV into computer, So what's your problem then?

I am not sure if I have a problem, that's why I am here to find out. VCR to Camcorder to PC. Scenalyzer shows dropped frames. I have no sync issues. Those are the facts. Question: Do I need to be worried about the dropped frame for whatever reason???

That VCR explanation you were given is wrong, or at least it was dumbed down to a point it became wrong, Audio and video are two separate things before entering the VCR, when they are recorded on tape and when they are played back from tape, and when going in to TV on a separate cables and processed on different circuit boards, the only relationship between audio and video is just timing. On broadcast TV in the other hand it's a different strory but that is unrelated to VCR.

Good to know.

[plehoediv]

I use Scenalyzer and from what I remember, I did not change any settings. The signal goes from my VCR (no TBC) to my Camcorder TRV820e with TBC and from there to my PC.

If you use a DV Converter to digitize the analog signal, the "classic" definition of inserted/dropped frames does not apply, and you have little control of what happens during the Analog to DV conversion.

Just to be sure: The conversion happens in the Camcorder, right? Has to be, because the signal going to the PC is via Firewire and that is digital.

The digital signal captured may show dropped frames while the stream is transferred to the PC via SCLive, which may happen for reasons related to the DV converter and/or the PC. They are somehow different from the inserted/dropped frames inherent to the Analog to Digital conversion

.

I don't get that. Can you please "dumb" it down a bit for me?

A check with AVPS DV Analyzer on the captured DV file is useful to check potential issues.

Ok, now you are throwing the word "issues" around, without really saying what makes what an issue!?

Thanks.

[lollo]

Just to be sure: The conversion happens in the Camcorder, right? Has to be, because the signal going to the PC is via Firewire and that is digital.

Yes, the Camcorder digitize the audio/video stream and compress it with DV codec. The digital signal is then transferred to the PC via firewire connection.

I don't get that. Can you please "dumb" it down a bit for me?

Because what said above, SClive will check the incoming digital stream while creating the dv avi file on the PC. If something is not correct (time code, frames, packets, ...) it will report so.
The digital stream is created in real time by the Camera reading the analog a/v inputs, and the transferred to the PC. It may happen that a problem arise in the player, in the Camera or in the PC, leading to dropped frames. The last concerns interfering CPU tasks, I/O activity, background processes, as already noted by Skiller.

Ok, now you are throwing the word "issues" around, without really saying what makes what an issue!?

When transferring a DV stream from tape to PC (or when converting an analog a/v to DV and then transferring it to PC) you look for dropped frames, frames with video error concealment and frame with DV timecode incoherency.

Here an example of a report from DV Analizer on one of my transfer with SCLive:

DV Analyzer v.1.4.0 by AudioVisual Preservation Solutions, Inc. http://www.avpreserve.com

C:\Sony DCR-PC6E\DV01\scene'20020102 16.31.58.avi

Frame Count: 11136

Frame count with video error concealment: 551 frames 
Total video error concealment:    172797 errors (  172797 "A" errors)
Frame count with DV timecode incoherency: 1 frames 

Absolute time	DV timecode range        	Recorded date/time range                         	Frame range
00:00:00.000	00:55:10:16 - 01:02:36:01	2002-01-02 16:31:58     - 2002-01-02 16:39:23    	       0 -    11135

Percent of frames with Error: 4.95%
Percent of frames with Error (including Arbitrary bit inconsistency): 4.95%
Percent of frames with Video Error Concealment: 4.95%
Percent of frames with Timecode Incoherency: 0.01%

[plehoediv]

Just to be sure: The conversion happens in the Camcorder, right? Has to be, because the signal going to the PC is via Firewire and that is digital.

Yes, the Camcorder digitize the audio/video stream and compress it with DV codec. The digital signal is then transferred to the PC via firewire connection.

Copy that.

I don't get that. Can you please "dumb" it down a bit for me?

Because what said above, SClive will check the incoming digital stream while creating the dv avi file on the PC. If something is not correct (time code, frames, packets, ...) it will report so.

That makes sense.

The digital stream is created in real time by the Camera reading the analog a/v inputs, and the transferred to the PC. It may happen that a problem arise in the player, in the Camera or in the PC, leading to dropped frames. The last concerns interfering CPU tasks, I/O activity, background processes, as already noted by Skiller.

Makes sense.

Ok, now you are throwing the word "issues" around, without really saying what makes what an issue!?

...you look for dropped frames, frames with video error concealment and frame with DV timecode incoherency.

But why? That is the part I don't get. What is that info going to do for me? In my case, I had as many as 20+ dropped frames (mostly 2-7), but no sync issue at the end of a 3h video. So why would I care? Unless someone tells me that the dropped frames are going to be an issue later down the road. Like when converting the footage to another codec, or when color grading, or when applying noise reduction, or editing. You know what I mean.

Here an example of a report from DV Analizer on one of my transfer with SCLive:

I will take a look. Thanks.

So, the bottom line is I now know why I might have dropped frames and how to find them, but I still don't know if it really is an issue. Are my dropped frames going to cause an issue when working on the footage later on, using other software?

Thanks.

[plehoediv]

EDIT: The point I was trying to make is kind of like having a dent in your car. That dent is there, you can see it, it will make the car less valuable, but it will NOT drive any different than without the dent, so it does not matter for the purpose of driving. Same with the dropped frames. There are there, I know why there are there, but I still don't know if there really make a difference when working with the footage later. Because as of now, just looking at the footage, I see no difference.

Thanks.

[lollo]

While inserted frames are there to compensate a hole and to keep a/v in synche, dropped frames are more critical, because a lot of them may cause aynsh a/v. That's why for analog capture of problematic tapes we recommend an external TBC. If you have < 5 frames not consecutive or in proximity of the same place there should be no issues. If more, check a/v synch at the end of the capture.

P.S. from a collector point of view, fom me having a dropped frame in a video is like having a comic book without a page (exaggeration); for your purposes, you can live with that

[plehoediv]

While inserted frames are there to compensate a hole and to keep a/v in synche, dropped frames are more critical, because a lot of them may cause aynsh a/v.

I understand. Luckily, I have no sync issues, but I am going to check what the default setting is on Scenalyzer. Inserting frames or not.

That's why for analog capture of problematic tapes we recommend an external TBC.

My TRV820E has TBC. I think it is "good enough" of a TBC for what I am doing. I also have a ES15 and EH55.

If you have < 5 frames not consecutive or in proximity of the same place there should be no issues. If more, check a/v synch at the end of the capture.

Scenalyzer has this feature where you can press N on your keyboard, and it will go the the next "error/dropped frame". Whenever I do that, I notice that 90% of all dropped frames are in the middle of transitions. You know, when one "tape" ends and another one begins, and it makes the tape have all that "static" or "streaks"...

P.S. from a collector point of view, fom me having a dropped frame in a video is like having a comic book without a page (exaggeration); for your purposes, you can live with that

LOL, I know what you mean. See, the problem is that I can start going down the rabbit hole deeper, and deeper, and deeper. It never ends. I have to be careful to not overdo it, because that is what I do. I actually got my PowerEdge T620 Server going again. Dual XEON E5-2697 V2, 64GB RAM and a 780Ti. 2 x SSD for OS and 4 x HDD for Data. I got a Firewire card in the mail the other day and I am going to install it today. Just to see if it is my old Laptop that is not able to capture fine, or if it is the VCR...

Thanks bro!

[lollo]

My TRV820E has TBC. I think it is "good enough" of a TBC for what I am doing. I also have a ES15 and EH55.

Generally we speak about (line)TBC for a TBC inside a VCR or a Camcorder, acting intra-frame and (frame)TBC for an external TBC acting inter-frame with higher buffering capabilities.

ES15 and EH55 are somehow in the middle. Sometimes they are good enough to stabilize a bad signal, sometimes a (frame)TBC is really needed. If in use, disable the (line)TBC of the Camcorder.

Now Bwaak will arrive and ask for an exact technical definition better than what I wrote

Whenever I do that, I notice that 90% of all dropped frames are in the middle of transitions. You know, when one "tape" ends and another one begins, and it makes the tape have all that "static" or "streaks"...

That's normal, no problem at all.

See, the problem is that I can start going down the rabbit hole deeper, and deeper, and deeper. It never ends.

Just capture the tape with dropped frames twice: if they are at the same instant in time, stop. Otherwise merge the "good" segments (DV is a intraframe only compressor).

[dellsam34]

LOL, I know what you mean. See, the problem is that I can start going down the rabbit hole deeper, and deeper, and deeper. It never ends. I have to be careful to not overdo it, because that is what I do.

In most cases DV is not a rabbit hole for the average user as long as you use type II with locked audio, It becomes a rabbit hole when you start nit picking, that's why a project like DV rescue came to life, but that's for serious archivists and mainly focuses on digital tapes, Analog tapes are better captured without involving a DV codec but that has it's own set of issues.

[plehoediv]

[QUOTE=lollo;2691622]

Generally we speak about (line)TBC for a TBC inside a VCR or a Camcorder, acting intra-frame and (frame)TBC for an external TBC acting inter-frame with higher buffering capabilities.

Copy that.

ES15 and EH55 are somehow in the middle. Sometimes they are good enough to stabilize a bad signal, sometimes a (frame)TBC is really needed. If in use, disable the (line)TBC of the Camcorder.

See, this is what I mean by going down the rabbit hole, because the last time I used both (EH55 and Camcorder) the TBC on the CC was turned on! Now you are telling me it should've been turned off. Now I got to redo the whole thing again, ha ha.

Now Bwaak will arrive and ask for an exact technical definition better than what I wrote

So what.

Whenever I do that, I notice that 90% of all dropped frames are in the middle of transitions. You know, when one "tape" ends and another one begins, and it makes the tape have all that "static" or "streaks"...

That's normal, no problem at all.

I wish I would have known earlier how to check for errors in Scenalyzer, so I could've seen where the dropped frames were. That way I would've realize they are very very often in those transitions and thus ignored them!

Just capture the tape with dropped frames twice: if they are at the same instant in time, stop. Otherwise merge the "good" segments (DV is a intraframe only compressor).

Thats the plan. When I see the dropped frame is at let's say 01:34:25, I cut the footage with Shutter Encoder right before the dropped frame and then start the tape right before that time and see if it drops again.

Anyhow, from what I can tell, dropped frames are not an issue. At least not in my case and I should stop f-ing around and just get the whole thing done.

Thanks.

[plehoediv]

[QUOTE=dellsam34;2691630]

In most cases DV is not a rabbit hole for the average user as long as you use type II with locked audio,

Everything with me is a rabbit hole. Unfortunately. I don't even know that type II with locked audio is?

It becomes a rabbit hole when you start nit picking,

Again, I do that with everything.

that's why a project like DV rescue came to life, but that's for serious archivists and mainly focuses on digital tapes,

What is that? A website?

Analog tapes are better captured without involving a DV codec but that has it's own set of issues.

What do you mean? Like with a USB Video Grabber or Capture Card?

Thanks.

[lollo]

What do you mean? Like with a USB Video Grabber or Capture Card?

Analog should be captured at YUV 4:2:2 lossless, with one of the recommended capture cards.

With the DV route, assuming the quality of the A/D conversion of the DV converter is equivalent to that of the capture card, you introduce a degradation because the DV compression (DV codec uses intraframe DCT, sensitive to VHS noise) and the chroma subsampling to 4:2:0 (PAL) or 4:1:1 (NTSC).

The difference in term of quality is minimal (but present). Search the forum for comparisons between analog lossless captures versus analog DV captures. Some example here:
https://forum.videohelp.com/threads/360804-DV-vs-lossless-capture-of-VHS

However, if a restoration is planned, a lossless capture is more appropriate and effective.

that's why a project like DV rescue came to life, but that's for serious archivists and mainly focuses on digital tapes,

What is that? A website?

An overview here: https://docs.google.com/presentation/d/1JFYHaKMZWHd8LFOVWmGuxdLNgFOiSXcoSxCMB-TXCvA/edit#slide=id.p

[Bwaak]

zAn overview here: https://docs.google.com/presentation/d/1JFYHaKMZWHd8LFOVWmGuxdLNgFOiSXcoSxCMB-TXCvA/edit#slide=id.p

HDV is not DV. MiniDV is just a cassette form-factor, not a subtype of DV. Maybe this slideshow would make more sense with the accompanying narration.

[lollo]

They may have done errors, but the whole concept is sound:
https://github.com/mipops/dvrescue
https://mipops.github.io/dvrescue/

[plehoediv]

What do you mean? Like with a USB Video Grabber or Capture Card?

Analog should be captured at YUV 4:2:2 lossless, with one of the recommended capture cards.

You are telling me now? LOL.

With the DV route, assuming the quality of the A/D conversion of the DV converter is equivalent to that of the capture card, you introduce a degradation because the DV compression (DV codec uses intraframe DCT, sensitive to VHS noise) and the chroma subsampling to 4:2:0 (PAL) or 4:1:1 (NTSC).

Copy that.

The difference in term of quality is minimal (but present). Search the forum for comparisons between analog lossless captures versus analog DV captures. Some example here:
https://forum.videohelp.com/threads/360804-DV-vs-lossless-capture-of-VHS

Will take a look. Thanks.

However, if a restoration is planned, a lossless capture is more appropriate and effective.

I guess I am going to "attempt" a restauration down the road. Hopefully by then AI will do it for me...

An overview here: https://docs.google.com/presentation/d/1JFYHaKMZWHd8LFOVWmGuxdLNgFOiSXcoSxCMB-TXCvA/edit#slide=id.p

Will check it out...

Thanks.

[plehoediv]

They may have done errors, but the whole concept is sound:
https://github.com/mipops/dvrescue
https://mipops.github.io/dvrescue/

Great. Thanks.