Maybe the question is pretty simple... I'm just curious.

Does anybody know what's going on? I downloaded the same fragments from the
camcorder a few hours later, got the same set of DV files, sizes are
absolutely equal. The byte to byte comparison shows that these files are not
equal and are having some minor differences like 1 byte every Kbyte or
something like that. Why? I was expecting that since these files have been
downloaded from the DIGITAL into DIGITAL with the same device and software
they should be absolutely identical. I'm not expecting we're writing
something time sensitive inside these files during download, then why I'm
seeing these differences? What it can be? One more time, I got two different
sets of files with the same file sizes, so that they are looking equal until
I compare the contents.

Just D.

"Just D" wrote in message
...
Maybe the question is pretty simple... I'm just curious.

Does anybody know what's going on? I downloaded the same fragments
from the
camcorder a few hours later, got the same set of DV files, sizes
are
absolutely equal. The byte to byte comparison shows that these
files are not
equal and are having some minor differences like 1 byte every Kbyte
or
something like that. Why? I was expecting that since these files
have been
downloaded from the DIGITAL into DIGITAL with the same device and
software
they should be absolutely identical. I'm not expecting we're
writing
something time sensitive inside these files during download, then
why I'm
seeing these differences? What it can be? One more time, I got two
different
sets of files with the same file sizes, so that they are looking
equal until
I compare the contents.


Is this from a DV tape, there could well be issues around the video
heads, as you say they are not huge and don't affect the playout -
just the actual file size.

Over to Tony Morgan...! :~)

On Sun, 3 Dec 2006 14:17:07 -0700, "Just D" wrote:

The byte to byte comparison shows that these files are not
equal and are having some minor differences like 1 byte every Kbyte or
something like that.

Interesting.

Is the difference an actual byte or just a single bit in the byte?

There are also some reserved and/or undefined words (two bytes) in the dv
headers which could contain random data.




regards

Stuart

www.mckears.com

I can make a screen shot if you want, although anybody can get this
difference I guess. It was something like "P" or "Q" in the comparison
window when I was comparing these files.

"Stuart McKears"
Is the difference an actual byte or just a single bit in the byte?

So there is mostly a one bit difference only and it's not very often, but
regular. Maybe yes, some kind of reserved byte in the frame header or
something.

There are also some reserved and/or undefined words (two bytes) in the dv
headers which could contain random data.

Maybe so, I hope that this is the reason.

The lengths of all correlating files from both file sets are same up to one
byte.

Just D.

Is the difference an actual byte or just a single bit in the byte?

So there is mostly a one bit difference only and it's not very often, but
regular. Maybe yes, some kind of reserved byte in the frame header or
something.

DV data is compressed (both audio and video), so I don't think it would be
very tolerant of a one-bit corruption (although I've no idea how good the
error correction is in a DV stream). The effect would be more noticeable in
the video than in the audio.

If the files are the same apart from a single byte at a consistent point,
perhaps it's something like the system time that the capture took place? I
suppose the way to test it would be to export a DV AVI from the timeline,
wait a bit, then export another, then compre the two...

.... in fact, I just did that - and sure enough the files are different. Two,
two-byte differences in a one-second (25 frame) AVI.

On Sun, 3 Dec 2006 17:08:57 -0700, "Just D" wrote:

I can make a screen shot if you want, although anybody can get this
difference I guess. It was something like "P" or "Q" in the comparison
window when I was comparing these files.

"Stuart McKears"
Is the difference an actual byte or just a single bit in the byte?

So there is mostly a one bit difference only and it's not very often, but
regular. Maybe yes, some kind of reserved byte in the frame header or
something.

There are also some reserved and/or undefined words (two bytes) in the dv
headers which could contain random data.

Maybe so, I hope that this is the reason.

The lengths of all correlating files from both file sets are same up to one
byte.

Just D.


Have a look at

http://download.microsoft.com/downlo...c/DVAVSPEC.RTF

You should be able to track the offending bits/bytes down.

Might take a bit of time but it'll give you something interesting to do over
Christmas :-)

Of course, that might be Christmas 2007 as decoding raw data can be sometimes
lengthy!!!!


regards

Stuart

www.mckears.com