Bug#718805: /usr/bin/avconv: avconv cannot grab video4linux2 device

[rpnpif]

Package: libav-tools
Version: 6:0.8.6-1~bpo60+1
Severity: important
File: /usr/bin/avconv

avconv -f video4linux2 -i /dev/video1
get this error :
avconv version 0.8.6-6:0.8.6-1~bpo60+1, Copyright (c) 2000-2013 the Libav developers
  built on Jul 23 2013 15:28:31 with gcc 4.4.5
avconv: /build/libav-_lRc_4/libav-0.8.6/libavutil/mathematics.c:79: av_rescale_rnd: Assertion `c > 0' failed.
Abort

But vlc (from squeeze-backports) works fine.
FFmpeg-1.2.2 from ffmpeg.org works fine with --disable-libv4l2, works with many warnings with --enable-libv4l2.

-- System Information:
Debian Release: 6.0.7
  APT prefers oldstable-proposed-updates
  APT policy: (500, 'oldstable-proposed-updates'), (500, 'oldstable')
Architecture: i386 (i686)

Kernel: Linux 3.2.0-0.bpo.4-686-pae (SMP w/1 CPU core)
Locale: LANG=fr_FR.UTF-8, LC_CTYPE=fr_FR.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages libav-tools depends on:
ii  dpkg                   1.15.8.13         Debian package management system
ii  libavcodec-extra-53    6:0.8.6-1~bpo60+1 Libav codec library (additional co
ii  libavdevice53          6:0.8.6-1~bpo60+1 Libav device handling library
ii  libavfilter2           6:0.8.6-1~bpo60+1 Libav video filtering library
ii  libavformat53          6:0.8.6-1~bpo60+1 Libav file format library
ii  libavutil51            6:0.8.6-1~bpo60+1 Libav utility library
ii  libc6                  2.11.3-4          Embedded GNU C Library: Shared lib
ii  libpostproc52          6:0.8.6-1~bpo60+1 Libav video postprocessing library
ii  libsdl1.2debian        1.2.14-6.1        Simple DirectMedia Layer
ii  libswscale2            6:0.8.6-1~bpo60+1 Libav video scaling library

libav-tools recommends no packages.

libav-tools suggests no packages.

-- no debconf information