[FFmpeg-user] [offtopic] expansion of video content

[Moritz Barsnick]

I may be somewhat off, but:

On Tue, Sep 24, 2019 at 11:15:39 -0600, JD wrote:
> Here is the info:
> # isoinfo -d dev=/dev/sr0
> CD-ROM is in ISO 9660 format
> System id:
> Volume id: ARV_NT5.1_DES
> Volume set id: UNDEFINED
> Publisher id:
> Data preparer id:
> Application id:
> Copyright File id:
> Abstract File id:
> Bibliographic File id:
> Volume set size is: 1
> Volume set sequence number is: 1
> Logical block size is: 2048
> Volume size is:

I don't see a number here. I assume the 4096640 you quote is usually
displayed here.

> Once I mount the drive:
> # mount -t iso9660 /dev/sr0 /sr0
> mount: /dev/sr0 is write-protected, mounting read-only
> # du -sk /sr0/video_ts/
> 25253528        /sr0/video_ts/
> Since that is in number of k's (1024 bytes)
> echo  "25253528 * 1024" | bc
> 25859612672
> 25859612672
>
> So how did a 4GB volume expand into  25GB?

I'm guessing here, from hearsay:

The former "isoinfo" shows you the raw disk size. 8 GB sounds
reasonable, as you wrote.

The latter "du" shows you the mounted file system. The value (probably)
represents whatever ISO9660 tells the driver.

You must understand that the ISO9660 file system is an *additional*
abstraction on the DVD. A real DVD video player does not know how to
read a file system, but rather uses other raw information to access its
tracks (or whatever you want to call them) correctly. On copy-protected
(video) disks, the ISO9660 file system is a big fake to fool programs
which mount the file system. Files may appear much larger than they
should be, stuff may be hidden, sectors with I/O erros may be included,
and so on.

IMO, you need to copy your images with something which operates on the
raw device, not on the file system.

Anyone: please correct me if I'm wrong. My experience with DVDs is a
bit aged. ;-)

Cheers,
Moritz