[mythtv-users] DVD ISO playback problems: Invalid IFO

Michael T. Dean mtdean at thirdcontact.com
Thu Jan 10 00:14:00 UTC 2008

On 01/09/2008 05:34 PM, kim Gross wrote:
>>> I would be willing to bet you are hitting deliberate bad sectors used to
>>> stop copying of the disc.
>> This is another place where dd_rescue can help.

I highly recommend using ddrescue instead of dd_rescue (yes, there's a 
difference--and it's a big one).

ddrescue:  http://www.gnu.org/software/ddrescue/ddrescue.html
dd_rescue: http://www.garloff.de/kurt/linux/ddrescue/

(keep reading for why)

>>   You can tell
>> dd_rescue to copy either forwards or in reverse.  If your encountering
>> bad sectors near the beginning of the disc, just copy in reverse.  It
>> won't truncate the data (unless you want it to) and you can still read
>> in the entire ISO.  Granted, reading in reverse is slower than
>> forward, but still much faster than waiting for the disc to error out
>> on each sector.
>> The finished image works just fine for a lot of my DVDs with similar
>> read errors.
> So do you read from the front to the error and then read from the back 
> to the error and put it together some how?  What if the disc has 
> multiple bad spots on it?  I am thinking that my Pirates III has 4 bad 
> spots rather than just one.

This is exactly what dd_rhelp ( 
http://www.kalysto.org/utilities/dd_rhelp/index.en.html ) was designed 
to do--it calls dd_rescue with appropriate arguments to recover as much 
data as possible without the user having to learn the details of dd_rescue.

However, note at the bottom of the dd_rhelp page:
We are all knowing that a quick C program should be better. So feel free 
to create it ! And this is what Antonio Diaz did for its "GNU ddrescue" 
program, make sure to have a look to it before using dd_rhelp.

And, above that in the "Important note" section:
For some times, dd_rhelp was the only tool (AFAIK) that did this type of 
job, but since a few years, it is not true anymore : Antonio Diaz did 
write a ideal replacement for my tool : GNU 'ddrescue'.

Yes, this is not very clever to have called a tool the same name that 
'dd_rescue' from Kurt Garloff (catch the subtle difference between 
'ddrescue' and 'dd_rescue' ?), but it seems that it was done by intent 
as we warned Antonio Diaz from the fact it would probably mess users in 
this tiny world of hard drive recovery tools.

Nevertheless, I really encourage you to use this replacement tool if it 
works for you (and it should be the case). Why ? Understand first what 
we are comparing :
- dd_rhelp (in bash script) + dd_rescue (in C) in one hand
- ddrescue (in C) in the other.

dd_rhelp was meant as a quick hack to implement what dd_rescue didn't 
do, and what couldn't be done at that time (AFAIK).

It could be some cases where ddrescue won't work, and this is the major 
reason why I keep maintaining dd_rhelp. It is important to tell me and 
Antonio Diaz when these cases occur.

Now that you are enlightened, you are free to use dd_rhelp.

/me wonders why distros still use dd_rescue instead of ddrescue (and, if 
installing dd_rescue, why they don't install dd_rhelp).


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