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We do not care about CPU arch and vendor when configuring NASM.
Comparing against the full host triplet anyway requires us to
either complicate checks or use more permissive patterns than necessary
introducing a dependency on the specific order of checks.
Notably GNU Hurd’s "gnu" name overlaps with the "-gnu" suffix
used for all glibc systems. This poses a problem for e.g.
kfreebsd-gnu which needs different settings than GNU Hurd.

By using just the actually relevant part, host_os, we can drop leading
globs (and hyphens) for all but *bsd*, avoiding this collision.

There are too many BSD variants to list all explicitly and a check
against canonical names used by config.guess suggest all matches to
*bsd* are actually BSD variants. In practice there are thus probably no
collisions to worry about, but to be extra cautious let’s put *bsd* at
the end.

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libass is a portable subtitle renderer for the ASS/SSA (Advanced Substation Alpha/Substation Alpha) subtitle format. It is mostly compatible with VSFilter.

Get it

See GitHub releases for the latest release 0.17.1 (released 2023-02-26). See the changelog for a detailed list of changes.

Source code is available from our GitHub repository.


Please use the issue tracker to report bugs or feature requests.

We have an IRC channel, too. Talk to us on Note that we cannot be online all the time and we cannot answer IRC questions if you leave the channel. Even if you do not get an immediate response, keep your IRC client open, and we will eventually get back to you.

Related Links

The following projects/companies use libass:

Information about the ASS format:

Other ASS/SSA implementations: