matroskadec: Fix a double negation typo

This typo has existed since this code was added in c16582579.
Newer versions of clang pointed out that this comparison always
was true (since the result of the negation is either 0 or 1, while
AVDISCARD_ALL has the value 48).

Signed-off-by: Martin Storsjö <martin@martin.st>
hevc: Use the local context variable when needed
lavf: document av_dump_format()
ismindex: Allow adding a path prefix to the generated .ism file

This allows storing the .ismv/.isma/.ismc files separately from
the .ism file on a server, without having to manually edit the
.ism file after generating it with the ismindex tool.

Signed-off-by: Martin Storsjö <martin@martin.st>
ismindex: Add an option for outputting files elsewhere than in the current directory

Signed-off-by: Martin Storsjö <martin@martin.st>
daud: split muxer and demuxer

Signed-off-by: Diego Biurrun <diego@biurrun.de>
id3v2enc: use a case-insensitive comparison for APIC picture type
webpdec: Fix decoding of the huffman group indices.

Per the specification, "The red and green components of a pixel
define the meta Huffman code used in a particular block of the ARGB
image."
x86: mpegvideoenc: Change SIMD optimization name suffixes to lowercase