[mythtv-users] OT DVD ripping software

[John Pilkington]

On 27/10/14 16:17, Stephen Worthington wrote:
> On Mon, 27 Oct 2014 16:25:58 +0100, you wrote:
>
>> AFAIK CDs don't have any error prevention/correction, so you need a tool to
>> handle reading errors while ripping. The OS won't report errors.
>
> Actually, audio CDs have two levels of error detection and correction.
> The problem is that it is not usually good enough to cover the sort of
> damage CDs collect in their old age.  Audio CD error correction is
> actually quite good, but when it was designed, no-one knew just how
> CDs would age and how bad the damage could get.  Pressed CDs last
> pretty well if treated right.  The rest are very vulnerable to light,
> heat, compression, damp, mould, ...
>
> I believe data CDs have only the lower level error correction of the
> two on audio CDs, which is way less capable than the higher level, and
> hence are much more vulnerable to errors.
>
> If there was no error detection or correction on CDs, then the OS
> would not be able to detect errors and would just have to accept
> whatever data it saw, except when the errors created obviously bad
> filesystem errors such as file pointers pointing beyond the end of the
> CD.
>
>> But DVDs have a normal file system - I always thought that there is no
>> problem concerning the reading quality. The OS and the DVD drive have
>> to handle reading errors. And if the disc isn't readable an error will be
>> reported.
>
> If you are using the filesystem then yes, errors will be reported.  dd
> does not use the filesystem.  It reads sectors directly.
>
>> But dd isn't a good tool for creating disc images???
>
> No.  Unless you check the logs after using dd, you may never know that
> a sector had a read error and the data it copied for that sector is
> bad.  Until you play the bit of the disk image with the error.  So use
> readom which does report errors and is designed for the job of ripping
> optical disks.

I just checked 'man readom' which speaks only of CDs and is 
'interesting' in other ways:-

'Also note that this version of readom (in el7) uses a modified libusal 
library which has a different behaviour compared to the one distributed 
by its original author.'   and

'Unless  you  want  to risk getting problems, readom should be run as 
root. If you don't want to allow users to become root on your system, 
readom may safely be installed suid root.'

.. but the config page of my installation of k3b looks as if will use 
readom -clone to get the data and growisofs to write it.  Have you tried 
it?