Videomaker – Learn video production and editing, camera reviews › Forums › Technique › Miscellaneous Techniques › Problem importing Hi-8 tape with Digital 8 Camcorder
- July 16, 2008 at 11:49 AM #37311nate3poParticipant
I’m going to leave certain details out of my story for the sake of keeping it short. Feel free to ask questions if you need me to fill something in. I have videos on 8mm and Hi-8 tapes that a I import via firewire from a Digital 8 camcorder. For those who don’t know you can import analog video recorded on 8mm and Hi-8 with certain digital 8 cameras through firewire and it will automatically convert it to a DV file on your computer. I’m in the US so my video is NTSC. Now we know that NTSC interlaced video displays the lower field and then the upper field. So if we numbered each field with field 1, field 2, field 3, field 4 and so on then the odd number would refer to the lower field and the even number to the upper field. Field 1 and field 2 would combine to make frame 1. So here’s my problem. Sometimes the video caputure seemed to combine the ending field of one scene with the beginning field of the next scene into one frame. But this did not always happen when capturing the same piece of video. I couldn’t understand why sometimes I had this problem and sometimes I didn’t, I decided to compare the problem clips with the none problem clips by analyzing each field in an editing program. I figured out a way to isolate each field so that the field that I did not want to see was replaced with black. If you want to know how I did this then ask. Anyway, what I discovered was that the difference between the two videos was that the fields were some one reversed. Lower field had been caputred as upper field and upper field capture as lower field. So essentially the video should have been captured as Frame 1 [field 1(lower) field 2(upper)], Frame 2 [field 3(lower) field 4 (upper)] was actually captured as Frame 1[field 2(lower) field 3(upper)], Frame 2[field 4(lower), field 5(upper)]. It was like some how the first lower field was lost so the computer took the second upper field and recorded it as if it were the first lower field. I hope this is making sense so far. I don’t always explains things well.
Before anyone says that it might have to do with the settings in my capture program, I should remind you that no settings were change between the correct recording the and problem recordings. In anycase, the first thing I want to know is if anyone has ever encountered this problem when try to capture 8mm tapes to a DV file by using a Digital 8 camcorder. I’m fairly certain that I have accurately determined the nature of the problem but have to admit it sounds slightly weird that an upper field could be confused with a lower field and vice versa by a camcorder.
I have noticed that this problem often occurs when I recorded the video with the following mistakes. Sometimes you want review what you’ve recorded, but before the days of the “end search” button you tried to reposition the tape back the right place manually. Of course what happens i that you don’t necessarily position the tape at the right point and you get part of the tape with no signal on it. I find that recordings that a preceded by this area of tape with no signal, I end up with the problem outlined above.
But I think I’ve found a fix for files captured with this problem. Adobe Premiere Pro has two functions called reverse field dominance and interlace consecutive frames. I discovered that when you reverse field dominance and render the file then take the rendered file and interlace consecutive frames you fix the problem. You just end up losing the first frame of the recording.
Diagram: each number represents the field number. Each column represents a frame and
2 4 6
1 3 5
Problem file (noticed how field one is missing and now field two takes field one’s place and field three takes field two’s place and so on)
3 5 7
2 4 6
Reverse field dominance the problem file(remember with NTSC video the lower field is place first, so even though the fields that should be lower are lower and the fields that should be upper are upper, they will play in the wrong sequence :3,2,5,4,7,6
2 4 6
3 5 7
Interlace consecutive frames for the file that has undergone reverse field dominance
4 6 8
3 5 7
What interlace consecutive frames did was take the upper field from each frame and shift them back so that they combined with the lower field of the previous frame.
- July 17, 2008 at 12:17 AM #165287AnonymousInactive
I think you answered your own question, you just didn’t know it.
First off, let’s discuss the linear recording. Before DV, in order to edit video from a given point, you had to have 3-5 seconds of stable video in front of the edit point. I can’t tell you how many times I had to tell my students they simply had to have the 3-5 second pre-roll before any video edit could be made. The pre-roll enabled the deck to reach the correct speed and synch fields so the system could write the new analogue signal to tape. Since we don’t edit from the tape anymore, we have to capture or digitize the signal. While most folks are unaware of it, digital tapes must also have a pre-roll before recording can start (so the tape can reach the proper speed.) And part of the pre-roll activity is to synch to the signal on tape.
Now when you use the Digital8 deck to read an analogue signal from tape, the deck itself recognizes the signal as analogue and switches to that mode. But when you hit that blank spot, the deck isn’t sure what to expect next. So it rolls along and hits the start of your new recording. It has to confirm it is still in analogue mode and start converting the signal. And that takes a little time. And it sounds like it is taking around 1/60 of a second to do that. So the signal doesn’t start converting until the second 1/60 of a second.
I bet you have already figured out that the 1/60 of a second delay corresponds to the missing field. The easy way to work around this problem is to slowly scan the tape till you have gone about one half a second into the new recording. Pause it, then start your capture. That should let the deck synch to the analogue signal and eliminate the problem.
I’m not exactly sure that answers your question. If it didn’t try rephrasing & adding to this posting.
Good luck & happy shooting.
- February 10, 2009 at 1:17 AM #165288AnonymousInactive
I remember having this problem years ago. I was using my Sony Digital 8 to import analog 8 into my computer. The rendered DVD were all “jerky”. I finally found out that analog was Upper field first and Digital 8 was lower field first. I was able to set it to render correctly in Sony Vegas Movie Studio by keeping that in mind. I just did an import of an analog tape from another camcorder (8mm) and it was fine with the lower field first….no clue why?
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