Emulator

What went wrong?
When dumping frames (i.e. capturing video) for any game with lossless FFV1 codec the following message is spammed in console output:
[ffv1 @ 0x7f911bf477e0] Provided packet is too small, needs to be X. (where X is e.g. 2781184)

Moreover the resulting capture is unreadable by any player. ffprobe output for framedump0.avi:
[..]
[avi @ 0x14701a0] Could not find codec parameters for stream 0 (Video: ffv1 (FFV1 / 0x31564646), 640x480): unspecified pixel format
Consider increasing the value for the 'analyzeduration' and 'probesize' options
framedump0.avi: End of file

What steps will reproduce the problem?

1. Compile Dolphin on Linux with newer versions of ffmpeg (details below).
2. Start up Dolphin, enable "Dump Frames" and "Frame Dumps use FFV1" in Graphics menu.
3. Play a game. Video output should be captured. Above message gets spammed in console.

Which versions of Dolphin did you test on?
Several. Among those are 3.0-735 (commit d33e48319f27a2b17271128408a125a3f14364e2) and current master (commit e37cb1fc7646a6047fabb0c52584be1b33872737).

Which version of Dolphin used to work?
None. The problem is caused by a change in ffmpeg (see below).

What are your PC specifications (example: Operating System, CPU and GPU)?
OS: Arch Linux x86_64
Kernel: Linux arch-desktop 3.11.1-2-ARCH #1 SMP PREEMPT Sun Sep 22 19:45:00 CEST 2013 x86_64 GNU/Linux
CPU: Intel(R) Core(TM) i5 CPU 750 @ 2.67GHz
RAM: 8GiB

64 or 32 bit Dolphin?
64-bit. Likely affects 32-bit as well.

Further information:
The problem first started appearing when Arch Linux switched to a more recent version of ffmpeg.
I bisected the commit that first caused trouble capturing (black screen, no output in console, hang): http://patches.libav.org/patch/38060/
This is the commit that causes above messages to be spammed to console output: http://patches.libav.org/patch/38926/
Note that since then Dolphin does not hang with a black screen anymore, but instead runs pretty normal aside from FFV1 error messages.