mpegvideo: Do REBASE_PICTURE with byte pointers

REBASE_PICTURE (more specifically, this half of it) takes a Picture
pointer that points into one larger struct, finds the offset of
that Picture within the struct and finds the corresponding field
within another instance of a similar struct.

The pointer difference "pic - (Picture*)old_ctx" is a value given
in sizeof(Picture) units, and when applied back on
(Picture*)new_ctx gets multiplied back with sizeof(Picture). Many
compilers seem to optimize out this division/multiplication, but
not all do.

GCC 4.2 on OS X doesn't seem to remove the division/multiplication,
therefore the new pointer didn't turn out to point to exactly
the right place in the new struct since it only had sizeof(Picture)
granularity (and the Picture is not aligned on a sizeof(Picture)
boundary within the encompassing struct). This bug has been present
before 47318953d as well - with H264, pointers to h->ref_list[0][0]
pointed to 88 bytes before h->ref_list[0][0] after the rebase. After
shrinking Picture, the difference ended up even larger, making
writes via such a Picture pointer overwrite other fields at random
in H264Context, ending up in crashes later.

This fixes H264 multithreaded decoding on OS X with GCC 4.2.

Fixes Bug: #439

Signed-off-by: Martin Storsjö <martin@martin.st>
(cherry picked from commit a65f965c04bfa27adedc0409c14cc05903f483d0)

Signed-off-by: Reinhard Tartler <siretart@tauware.de>
qdm2: check array index before use, fix out of array accesses

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

(cherry picked from commit a7ee6281f7ef1c29284e3a4cadfe0f227ffde1ed)

CC: libav-stable@libav.org

Signed-off-by: Reinhard Tartler <siretart@tauware.de>
(cherry picked from commit 39bec05ed42e505d17877b0c23f16322f9b5883b)

Signed-off-by: Reinhard Tartler <siretart@tauware.de>
roqvideodec: check dimensions validity

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 3ae610451170cd5a28b33950006ff0bd23036845)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit fee26d352a52eb9f7fcd8d9167fb4a5ba015b612)

CC: libav-stable@libav.org

Signed-off-by: Reinhard Tartler <siretart@tauware.de>
(cherry picked from commit 488f87be873506abb01d67708a67c10a4dd29283)

Signed-off-by: Reinhard Tartler <siretart@tauware.de>
vqavideo: check chunk sizes before reading chunks

Fixes out of array writes

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit ab6c9332bfa1e20127a16392a0b85a4aa4840889)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 13093f9767b922661132a3c1f4b5ba2c7338b660)

CC: libav-stable@libav.org

Signed-off-by: Reinhard Tartler <siretart@tauware.de>
(cherry picked from commit f7d18deb73d1dd1b27b2c7062c9a10d168a6c62a)

Signed-off-by: Reinhard Tartler <siretart@tauware.de>
doc: Fix some obsolete references to av* tools as ff* tools

Signed-off-by: Diego Biurrun <diego@biurrun.de>

CC: libav-stable@libav.org
(cherry picked from commit 202b5f6deb65e405b07b9b5c20f97c8cb925cf49)

Signed-off-by: Reinhard Tartler <siretart@tauware.de>