Does transfering back to mini dv tape loose quality??

[Rudyard]

Ok I have been filming my little boy in little bits over the first 5 weeks of his life on my Sony HDR-HC3 HDV video camera.

I have taken about 35min of him before we had some friends over....a few beers, some footy and then some texas hold em poker to which we taped about 20mins of the game for some fun.

So now I have only 5mins left on my mini DV tape. And last night I took some more funny moments of my boy.

I am planning on keeping my mini DV tapes so that eventually when there is media/format affordable I can transfer my tapes in the HD i recorded them in rather than SD (for the timebeing I will put them on DVD) but I dont want to keep the poker night, it is just a bit of fun that is fine in SD, was in bad light and is not important at all.

So I want to take the poker night off, put it on DVD for us to laugh at, then take off the part of my son after the poker night but transfer it back to the miniDV tape recording over the poker night so that all my footage is in correct order and I can continue recording over until I eventually fill the tape with memories I actually want to keep.

Can I transfer back and fourth from my camera with no editing or anything just the digital data to my tape with no loss of quality (its just sending and recording 1's and 0's isnt it??)

[edDV]

If it were DV format the answer would be yes. For HDV format I'd have to say "It depends" and I'll try to find out more. Others may know.

HDV uses MPeg2. It records to tape and sends to the computer as a MPeg2 stream. Software is required to convert the stream into a file for storage on the hard disk drive. That is were loss could occur. Editing most likely will cause some loss. What software are you using to transfer data to the computer and edit?

[MOVIEGEEK]

As long as you are transfering DV-AVI there should be no loss.

[Rudyard]

I can capture with ulead video studio 9 or Vegas 4.0.
If it is better I know people with Premier Pro and can use there PC if need be.

I wont be editing at this point, I just want to transfer back to the tape for storage at original quality until high definition media and format are available (and affordable).

My PC specs if it has any bearing are:
3.0ghz intel dual core, 2gb ram, 256mb leadteck 7800 video card, 2 160gb hdd (one for capture, one for programs and editing).

[JohnnyMalaria]

The only thing that might cause problems is if your camcorder's heads start to get dirty or if the tape itself has "drop outs". The DV specification details how to hide bad data and, for the most part, you will never know that errors are being hidden.

If you were to go back and forth enough times with less-than-optimal heads, you might have issues.

Many DV camcorders will tell you, though, if the error rates are getting sufficiently high that a good head clean is needed...

(For the HDV, since it is MPEG2, you'll probably need to be very careful about where you make any cuts - ideally every "I" frame).

[gadgetguy]

Is it really worth the trouble? Tapes are cheap and you can edit out the card game later when you transfer to new media.

[Rudyard]

Sure I could keep it on there, but if it does not loose quality it really isnt any trouble.

Simply capture to PC - Export back to tape. The computer would do all the work and in just a few clicks I would have my tape ready to go.

[edDV]

Sure I could keep it on there, but if it does not loose quality it really isnt any trouble.

Simply capture to PC - Export back to tape. The computer would do all the work and in just a few clicks I would have my tape ready to go.

Go ahead and try it and see if you see any decline in quality. Your question was is there any loss and with MPeg2 that depends on how the software handles it.

Neither Ulead Video Studio 9 nor Vegas 4.0 made any claims for handling HDV losslessly. They probably handle HDV just like they do any other MPeg2 import. They decomperss it to RGB for a look and do something with it when you export. Maybe they re-export the original file, maybe they recompress. Odds are the software isn't lossless. But it may be fine for your needs.

VS10 and Vegas 6 have specific support for HDV but you need to read all their tech papers to understand how. Vegas is targeted at editing, filtering and effects so their focus is to make multigeneration and process calculation as lossless as possible using Cineform digital intermediates or "smart render" technology.

[stars]

Hi..
Isnt it possibel to cut out the unwanted parts directly form the mpg2 stream...
I dont know how the HDV mpeg2 stream works but with ordinary mpeg2 streams there is possible to
make cuts without rendering...

I use projectx to demux the video and audio and for the cutting mpeg2schnitt (which is frame accurate)..

Cuting and joining (must be same res. and audio format) without any problems...

and for the mux I think ImagoMPEG-Muxer should work or other program...

It depends on what type of audio you have in the original mpeg2 stream.

a hint....

stars....

[MOVIEGEEK]

It's best to edit in DV-AVI,MPEG-2(at ~8,000mbps) is ok but you will probably lose quality and add artifacts.

[Cornucopia]

MOVIEGEEK, the OP was talking about HDV, which is HiDef MPEG2 in a Transport Stream stored on DV tape. When you're talking about DV-AVI, it is somewhat misleading, because that would entail losing the HD quality and dropping down to SD--NOT what the OP wants to do (at least for the sections he wants to keep).

1st, you need to see if Vegas/PP2/etc can capture the MPEG2TS directly, or whether it transcodes to an Intermediate editing codec (like the Cineform).

If yes, continue on...If no, You're out of luck.

2nd, you need to see if the editing app will edit only on the I-frame (and thus avoid re-compression), or whether it recompresses the partial frame, or whether it compresses everything.

If A, continue on..If B, continue on, realizing that some frames will be compromised...If C, It's ALL going to be compromised--you'll have to decide yourself whether this is acceptable to you.

3rd, you need to see if the editing app has rollback capability for HDV (just because it can capture doesn't mean it can also do the reverse).

If so, you're ready to roll back with confidence...If not, you're out of luck.

Personally, it doesn't seem worth it. So you have to buy an additional DV tape??
You'll want to do that anyway just to test this out 1st to see if it'll work right---you surely don't want to test it out on the original without knowing, now do you?

Scott

[Rudyard]

Thanks for the reply.....it seems more complex because it is HDV (i assumed it would be the same as DV, just in HD).

Maybe it isnt worth the trouble but i may do it with another tape just for the excercise to see what happens.

Thanks everyone for their help.

[bobkart]

I am under the impression that I can transfer the contents of an HDV tape to PC, do nothing to the resulting file on the PC, and transfer it back to the camcorder (to another tape for example) with no loss of quality, i.e. bit-for-bit copies at each step. I guess this is not exactly what was originally asked (some editing was involved in that question, or at least splitting it up). But I am trying to get confirmation that there is really no loss in either direction, otherwise I'll have to revise my understanding of how this works (which I think is basically the same as with DV material).

[Rudyard]

I am under the impression that I can transfer the contents of an HDV tape to PC, do nothing to the resulting file on the PC, and transfer it back to the camcorder (to another tape for example) with no loss of quality, i.e. bit-for-bit copies at each step. I guess this is not exactly what was originally asked (some editing was involved in that question, or at least splitting it up). But I am trying to get confirmation that there is really no loss in either direction, otherwise I'll have to revise my understanding of how this works (which I think is basically the same as with DV material).

That is exactly how I thought it would be, I havent been able to test though as it seems none of my software with recognise the camera when in HDV mode and I have to change the output to convert to DV before any software with transfer it. Looks like I need to upgrade my software before I can do anything with my HDV footage (i tried it on vegas 5.0, ulead video studio 9 and on a friends Premier Pro 1.5, nothing recognises the HDV!)

[bobkart]

Apparently HDVSplit will transfer HDV files in either direction, although I've only used it to transfer from camcorder to PC.

In another Topic I asked about applications that could deal with HDV files and both Vegas and Premiere were mentioned (if I recall correctly). Also, waagg has indicated that Ulead can author the HDV files directly to an HD-DVD file structure suitable for playback on an HD-DVD Player (such as the Toshiba model whose number I forget).

[edDV]

I am under the impression that I can transfer the contents of an HDV tape to PC, do nothing to the resulting file on the PC, and transfer it back to the camcorder (to another tape for example) with no loss of quality, i.e. bit-for-bit copies at each step. I guess this is not exactly what was originally asked (some editing was involved in that question, or at least splitting it up). But I am trying to get confirmation that there is really no loss in either direction, otherwise I'll have to revise my understanding of how this works (which I think is basically the same as with DV material).

It is not like DV format. Although it is transferred in a way to make the stream look like a DV stream, the actual video and audio are a HDV MPeg2 stream with medium GOP (groups of frames) between I frames. It behaves like MPeg2 not like DV.

What part of this are you having difficulty understanding?

While it is possible to maintain the integrity of a MPeg2 stream, the software has to support that. Most editing software decompresses MPeg2 on import. So as said before, it depends on the software you use to transfer the stream to a file and then retransmit from the file as a stream back to the camcorder.

You need to start talking to Sony Support and your software company's support to get an answer to your need. I'm sure such software exists but don't assume.

Even if the MPeg2 stream does go through decompression and recompression (loss of one generation) it will most likely look fine to you. Anything you edit of filter will loose a generation as well. Smart software will minimize generation loss through the edtiting process. Non-smart software will repeat the decompression - recompression unnecessarily.

DV will hold up for seven or more generations. MPeg2 will loose quality each recompression.

[edDV]

Apparently HDVSplit will transfer HDV files in either direction, although I've only used it to transfer from camcorder to PC.

In another Topic I asked about applications that could deal with HDV files and both Vegas and Premiere were mentioned (if I recall correctly). Also, waagg has indicated that Ulead can author the HDV files directly to an HD-DVD file structure suitable for playback on an HD-DVD Player (such as the Toshiba model whose number I forget).

All that is true* but Rudyard wants no generation loss. That needs verification for each program mentioned.

Rudyard wants to transfer a tape to a file and then transfer portions of the file back to another tape and he wants a first generation copy like he would get from DV format. Alternatively, he might transfer only the clip he wants to a file and then re-export back to tape from that file.

*except I can't find a feature in HDVSplit for streaming a file back to the camcorder. HDVSplit requires an MPeg2 decoder for monitoring. I think the odds are good it doesn't decode the actual stream before writing the file but that question needs to be asked.

[bobkart]

I am under the impression that I can transfer the contents of an HDV tape to PC, do nothing to the resulting file on the PC, and transfer it back to the camcorder (to another tape for example) with no loss of quality, i.e. bit-for-bit copies at each step. I guess this is not exactly what was originally asked (some editing was involved in that question, or at least splitting it up). But I am trying to get confirmation that there is really no loss in either direction, otherwise I'll have to revise my understanding of how this works (which I think is basically the same as with DV material).

It is not like DV format. Although it is transferred in a way to make the stream look like a DV stream, the actual video and audio are a HDV MPeg2 stream with medium GOP (groups of frames) between I frames. It behaves like MPeg2 not like DV.

What part of this are you having difficulty understanding?

I understand all that just fine. But that does not answer my question.

Here's my question, to which I am not hearing an answer. Is the digital information on the tape the same as that which results from transferring the tape to a file on a PC? Or at least losslessly close. Yes I understand that MPEG compression is lossy. So is DV. I am not talking about dealing with the file in any way on the PC. Copy to PC, copy back, all I want to know is whether you get the same thing on the tape as what you started with on the tape. With DV you do even though DV is not lossless (encode an uncompressed video file to DV, and go back to uncompressed, you do not get the same video generally speaking.) HD MPEG-2 is also lossy in the same sense (and more so as you point out). But you can copy DV from camcorder to PC and back and get the same thing on the tape that you started with. If this characteristic is not true of HDV then just say so. Unless of course you don't know (which it sounds like is the case from your first reply in this Topic).

If the MPEG compression used to represent HDV happens BEFORE it gets to the tape, then transferring that data to a PC does/may not require any additional encoding of a lossy nature. That is the sense by which I mean that "I think it works like DV". I know "DV is not HDV". I'm just trying to find out of it has the same characteristic as DV in the sense that I have described.

[bobkart]

*except I can't find a feature in HDVSplit for streaming a file back to the camcorder.

Now that you mention it, I don't see it either. The second tab, which I thought was the reverse direction, is something else.

But the camcorder can take HDV in. So it could easily be that with an application that can send an HDV file, the original data could be restored after a round trip. Again, I understand the part about how any processing you do on the PC will not be lossless.

[edDV]

Here's my question, to which I am not hearing an answer. Is the digital information on the tape the same as that which results from transferring the tape to a file on a PC? Or at least losslessly close.

HDV carries the same digital information up to the PCIbus. From there it gets loaded into memory under control of the program you are using. From then on the writers of that program can decompress only for monitoring while keeping the original stream entact for the file or not. If the stream makes it into the file entact, then software can be written to restream from that file to the camcorder without generation loss. The question on the table is has anybody written software that way?

Importing the file to an editor usually causes the file to be decompressed to RGB or YUV thus loosing a generation. Any program that allows cutting on other than I frames must decompress at least in the GOP.

Yes I understand that MPEG compression is lossy. So is DV. I am not talking about dealing with the file in any way on the PC. Copy to PC, copy back, all I want to know is whether you get the same thing on the tape as what you started with on the tape.

As said above you need to ask the software writer in each case.

With DV you do even though DV is not lossless (encode an uncompressed video file to DV, and go back to uncompressed, you do not get the same video generally speaking.)

There are many programs that will do what you want with DV format starting with WinDV and DVIO. There are also DV native editors like Vegas and Premiere Pro that will keep DV format first generation even from the timeline.

There are a few MPeg2 editors that only decode between I frames. But we digress.

You need to comfirm your spec with the writer of the software.

... If this characteristic is not true of HDV then just say so. Unless of course you don't know (which it sounds like is the case from your first reply in this Topic).

True I don't know. Until confirmed by the writer of the software, it is prudent to assume these programs operate with HDV the same way they work with MPeg2 and that usuaully means they decompress before streaming an output.

If the MPEG compression used to represent HDV happens BEFORE it gets to the tape, then transferring that data to a PC does/may not require any additional encoding of a lossy nature. That is the sense by which I mean that "I think it works like DV". I know "DV is not HDV". I'm just trying to find out of it has the same characteristic as DV in the sense that I have described.

The only thing HDV shares with DV is the IEEE-1394 transport streaming layer. Look at some of these paragraphs from
http://www.myvtp.com/htm/hdvquest2.htm

"To edit any of the HDV-type MPEG-2 based compressed High Definition formats with HDV friendly software, you may need the latest versions of software and hardware, and IEEE 1394 (OHCI compliant firewire I/O). The HDV protocols HDV uses in the I-Link interface are different than the DV protocols as HDV requires IEC-61883-4 compliance, as well as other AV/C drivers. HDV protocols are incorporated with IEC-61883 transport stream interfacing, not FAM (or File Access Mode). That is why there is a hardware switch on both the Sony HVRZ1U and JVC GY-HD100 camcorders, to select between DV protocols and HDV protocols. You'll find this same switch on both the Sony HVRM10U VTR and the JVC BR-HD50U VTR as well. In the JVC DVHS SRVD400US units, this "switch" is done in software in the "DVHS" mode select, and it can be a bit tricky to set up.

One should bear in mind that the ability to transfer content between supporting devices does not in and of itself guarantee that original source time code will transfer across, or be recognized by the receiving device.

Sometimes, the requirement for the NLE is to actually have IEEE-1394 (firewire I/O) on the computer motherboard itself, as opposed to simply a PCI plug-in board such as from Belkin. This is not a requirement with Sony Vegas software, but is a requirement with one of the Pinnacle Liquid products. Editing and manipulating HDV video with effects and titles and in different frame rates is a separate matter.

HDV friendly software either works in one or both of two modes: that of the native HDV specified compressed file format, or, a special version of compressed file format that is friendly to the application software and the I/O hardware itself. If it is not HDV friendly, one would have to capture the video as either component analog HD or HD-SDI with an appropriate I/O capture card, and then edit in uncompressed mode. Output in uncompressed HD is of course not assured, because it depends upon the power of the host platform, the I/O breakout, and how the application software recognizes the I/O boards."


The more you read the more you realize HDV is very different and you can't assume anything short of asking the writer of the software or read his documentation.

What is needed is a program like WinDV that does the same thing with with HDV format.
Write Petr Mourek and ask if he is working on WinHDV.

[bobkart]

Okay thanks for that.

It may be easiest to answer this empirically. Once I find an application that will transfer HDV files to an HDV camcorder over IEEE1394, I will run that experiment. I think it is pretty safe to say that if I'm able to transfer from the camcorder something (sufficiently interesting content-wise) that I sent to it originally from PC, and the result of the second transfer compares successfully to the original, that we have confirmed my hypothesis. Or have I missed something else?

And finally, who can direct me to an application that can write an HDV (*.m2t) file over FireWire to an HDV camcorder?