[FFmpeg-user] slice and enabling slicecrc in FFv1

[Dinah Handel]

Dear FFmpeg-users,

I’m currently testing different specifications of FFv1: enabling each slice
options, and enabling and disabling slicecrc. The purpose of these tests is
to see whether or not enabling these options makes a significant difference
in processing times or the resilience of the resulting files for long-term
storage. However, in running these tests, it seems that the error
concealment used when slicecrc is enabled on a damaged slice is not working
as intended.

We conducted tests where the asset had every possible slice option (4, 6,
9, 12, 16, 24, 30) and slicecrc enabled and disabled. We then intentionally
created errors using zuff.

We analyzed at the results using the tblend filter (which makes it easier
to see when a slice uses error concealment since the difference within the
slice from one frame to the next will be null) and found the following
results:

   1.

   Frequently, there is a pattern where half of a slice shows an error, but
   the other half is concealed. However, the size of the concealment is a
   whole slice, and half of the proximate slice is also concealed. (see
   image <https://drive.google.com/open?id=0Bz3DvN4RErGdem5xTkFyRzZmNTg>)
   2.

   There is also a pattern that affects three slices, where one slice is
   concealed, and then a slice in the middle has no errors, and then the slice
   on the other side has an error. (see image
   <https://drive.google.com/open?id=0Bz3DvN4RErGddWVpeTlKQVl5Rnc>)
   3.

   In some cases, there are two slices directly next to one another, where
   one is concealed, and the other shows the error. (see image
   <https://drive.google.com/open?id=0Bz3DvN4RErGdUl9jVnEtYkNhTTg>)
   4.

   In a few cases, it appears that slicecrc identified the correct slice
   and worked as intended. (see image
   <https://drive.google.com/open?id=0Bz3DvN4RErGdZXozdElPQjFUa1k>)


Results indicate that often, the concealment intended to cover the error
did not successfully cover the area affected, when slicecrc was enabled.
Instead, the concealment was placed proximate to the error. It also appears
that errors affect a portion (half) of a slice, and the concealment covers
the other half, and half of another slice.

Questions:
Does this issue have to do with the specification of the number of slices?
Or, is slicecrc not accurately identifying the slice that contains errors?

If you're interested in viewing a few of the damaged and undamaged assets,
they may be found in this shared folder
<https://drive.google.com/folderview?id=0Bz3DvN4RErGdVjJjbkNHeS1pdW8&usp=sharing>,
along with the images linked above. Thanks for your assistance and feedback!

Dinah

-- 
Dinah Handel, MLIS | NDSR-NY @ CUNY TV
Linked In <http://www.linkedin.com/pub/dinah-handel/79/799/218> |
@dinahhandel <https://twitter.com/DinahHandel>