[FFmpeg-devel] [RFC] AAC nonmeaningful window sequences

Alex Converse alex.converse
Thu Jul 1 06:29:50 CEST 2010

For a long time we've spammed a warning and ignored the spec when an
AAC non-meaningful window transition is encountered (e.g. ONLY_LONG ->
SHORT[1], oddly we don't warn about the reverse) The authors have made
it clear that non-meaningful window transitions should be handled
naively. They even included some non-meaningful transition test
vectors (al03*). When asked to clarify they have stuck to this

We do a fancier fixup where we force windows to match. (e.g. ONLY_LONG
-> SHORT becomes START ->SHORT). Still I get bug-reports about this.
Most people see the warning and hear an artifact but not and artifact
in comparison to the spec's method and report a bug. I'm wondering if
we should remove the warning, make the warning consistent, or
implement the transitions as the spec requires.

[1] A false warning is generated if the first frame uses a short window sequence
[2] http://lists.mpegif.org/pipermail/mp4-tech/2003-June/002339.html

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