Re: Script to conditionally find and compress files recursively

Anssi Saari <anssi.saari@usenet.mail.kapsi.fi> wrote:

J Newman <jenniferkatenewman@gmail.com> writes:
 

It's true that you cannot tell within the first 5 seconds what the
ultimate compression ratio will be, but it seems to me (from
compressing avi/mp4/mov files with lzma -9evv) that you can tell
within +/- 5% to a high degree of confidence, what the ultimate
compression ratio will be given the first 5 seconds.

 
Well then, I believe the solution was already posted. Grab 5% of your
files with dd and see how it compresses.

The solution that I see grabs the first 1MB, but it would make more
sense to sample eg. 1% of the file size in five places within the
file. 100MB file = 1MB sample, 100MB/5 = 20MB, so use dd to grab
one 1MB sample from the start of the file then four more at an
offset that increments by 20MB each time. Store these separately,
compress them separately, then average the compression ratio of all
the samples.

I'm a little curious, what kind of space savings do you expect to get by
doing this? And wouldn't it make more sense to re-encode for lower
bitrate if space saving is your goal?

Maybe he's using lossless video compression? Otherwise yes it seems
like the wrong approach.

--
__          __
#_ < |\| |< _#