[ffmpeg] re-roll ffmpeg to 346d30b3f6631f2d47fa310f7dfeb78215706fc3

This is an update for a previous roll (fxr/807596) to the same
Chromium ffmpeg commit. Due to issues described and addressed in
fxr/816074, that roll caused some tests to fail, so the prebuilts
could not be rolled into fuchsia main.

This CL contains the results of an updated roll with fxr/816074 in
place. A manual test verifies that the problematic tests are passing
with this update. Chromium's ffmpeg repo is still on the same commit,
so there's no need to update that.

Change-Id: Ieb2c8af04fc94390a789e2f6f19d42c6657f870c
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/ffmpeg/+/816031
Reviewed-by: Petr Hosek <phosek@google.com>
12 files changed