[vdr] Hard link cutter [was: Suggestion: High speed cutting]
udo_richter at gmx.de
Sat Mar 17 15:35:22 CET 2007
Udo Richter wrote:
> I've been thinking about video cutting strategies, and I think its
> possible to speed up the cutting process noticeable, with some
> modifications to VDR.
I just had to do this in self-reply. ;)
For reference, this is my 'original' post:
This has been in my mind for over two years, and now I just wanted to
see it working: Using hard file system links to speed up editing
whenever a 00x.vdr file is copied from source to destination recording
A first patch is available on my web page:
Though the patch has been working for a week for me very well, it is
HIGHLY EXPERIMENTAL and should be used with caution. The patch is
COMPLETELY UNTESTED and NOT ADAPTED for multiple /videoxx folders. The
safety checks should prevent data loss, but hard linking may fail more
often than necessary.
While editing a recording, the patch searches for any 00x.vdr files that
dont contain editing marks and would normally be copied 1:1 unmodified
to the edited recording. In this case the current target 00x.vdr file
will be aborted, and the cutter process attempts to duplicate the source
file as a hard link, so that both files share the same disk space. If
this succeeds, the editing process fast-forwards through the duplicated
file and continues normally beginning with the next source file. If hard
linking fails, the cutter process continues with plain old copying. (but
does not take up the aborted last file.)
After editing, the un-edited recording can be deleted as usual, the hard
linked copies will continue to exist as the only remaining copy.
To be effective, the default 'Max. video file size (MB)' should be
lowered. The patch lowers the smallest possible file size to 10mb,
though this limits the recording length to 10*255 Mb (~100 minutes). A
value of 100mb is a good compromise between speed improvement and
recording length (~16 hours).
The patch must be enabled in Setup-> Recordings-> Hard Link Cutter. When
disabled, the cutter process behaves identical to VDR's default cutter.
There's a //#define HARDLINK_TEST_ONLY in the cutter.c file that enables
a test-mode that hard-links 00x.vdr_ files only, and continues the
classic editing. The resulting 00x.vdr and 00x.vdr_ files should be
identical. If you delete the un-edited recording, dont forget to delete
the *.vdr_ files too, they will now eat real disk space.
Note: 'du' displays the disk space of hard links only on first
appearance, and usually you will see a noticeably smaller size on the
To solve the file size vs. recording size conflict, dynamic file sizes
could be implemented, so that a recording starts with small file sizes,
and increases the file size at some point to ensure enough space for
huge recordings before 255.vdr is reached. For example, using 32Mb up to
192.vdr and 2000mb from 193.vdr on will give a total of 128 Gb or 84
hours, while using small files for up to 4 hours.
To support multiple /videoxx folders, the hard link must be placed on
the same disk as the source file. This requires a more advanced linking
Since original and edited copy share disk space, free space is wrong if
one of them is moved to *.del. Free space should only count files with
hard link count = 1. This still goes wrong if all copies get deleted.
For more safety, the hard-linked files may be made read-only, as
modifications to one copy will affect the other copy too. (except
deleting, of course)
SetBrokenLink may get lost on rare cases, this needs some more thoughts.
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