VDR-HLCUTTER README


Written by:           Udo Richter
Available at:         http://www.udo-richter.de/vdr/patches.html#hlcutter
                      http://www.udo-richter.de/vdr/patches.en.html#hlcutter
Contact:              udo_richter@gmx.de



About
-----

The hard link cutter patch changes the recording editing algorithms of VDR to
use filesystem hard links to 'copy' recording files whenever possible to speed
up editing recordings noticeably.

The patch has matured to be quite stable, at least I'm using it without issues.
Nevertheless the patch is still in development and should be used with caution. 
The patch is EXPERIMENTAL for multiple /videoxx folders. The safety checks 
should prevent data loss, but you should always carefully check the results.

While editing a recording, the patch searches for any 00x.vdr files that don't
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 1mb. Since VDR only 
supports up to 255 files, this would limit the recording size to 255Mb or
10 minutes, in other words: This setting is insane!

To make sure that the 255 file limit will not be reached, the patch also 
introduces "Max. recording size (GB)" with a default of 100Gb (66 hours), and 
increases the file size to 2000Mb early enough, so that 100Gb-recordings will
fit into the 255 files.

Picking the right parameters can be tricky. The smaller the file size, the 
faster the editing process works. However, with a small file size, long 
recordings will fall back to 2000Mb files soon, that are slow on editing again.

Here are some examples:

Max file size:      100Gb   100Gb   100Gb   100Gb   100Gb   100Gb   100Gb
Max recording size: 1Mb     10Mb    20Mb    30Mb    40Mb    50Mb    100Mb

Small files:        1-203   1-204   1-205   1-206   1-207   1-209   1-214
  GBytes:           0.2     2.0     4.0     6.0     8.1     10.2    20.9
  Hours:            0.13    1.3     2.65    4       5.4     6.8     13.9

Big (2000mb) files: 204-255 204-255 206-255 207-255 208-255 210-255 215-255
  GBytes:           101.5   99.6    97.7    95.7    93.8    89.8    80.1
  Hours:            67      66      65      63      62      60      53

A recording limit of 100Gb keeps plenty of reserve without blocking too much
file numbers. And with a file size of 30-40Mb, recordings of 4-5 hours fit into
small files completely. (depends on bit rate of course)



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 videodir.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, don't 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 edited recording.


History
-------

Version 0.2.0
  New: Support for multiple /videoXX recording folders, using advanced searching
       for matching file systems where a hard link can be created.
       Also supports deep mounted file systems.
  Fix: Do not fail if last mark is a cut-in. (Again.)

Version 0.1.4
  New: Dynamic increase of file size before running out of xxx.vdr files
  Fix: Last edit mark is not a cut-out
  Fix: Write error if link-copied file is smaller than allowed file size
  Fix: Broken index/marks if cut-in is at the start of a new file
  Fix: Clear dangling pointer to free'd cUnbufferedFile, 
       thx to Matthias Schwarzott

Version 0.1.0
  Initial release




Future plans
------------

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.