$ $ ffprobe -v debug -show_format -show_streams out_mp4-webm.webm 
ffprobe version 1.0.1 Copyright (c) 2007-2012 the FFmpeg developers
  built on Dec  6 2012 12:04:11 with gcc 4.6 (Ubuntu/Linaro 4.6.3-1ubuntu5)
  configuration: --prefix=/usr/local/ --enable-shared --enable-avfilter --enable-libvorbis --enable-pthreads --enable-libvpx --enable-gpl --enable-pic
  libavutil      51. 73.101 / 51. 73.101
  libavcodec     54. 59.100 / 54. 59.100
  libavformat    54. 29.104 / 54. 29.104
  libavdevice    54.  2.101 / 54.  2.101
  libavfilter     3. 17.100 /  3. 17.100
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 15.100 /  0. 15.100
  libpostproc    52.  0.100 / 52.  0.100
[matroska,webm @ 0x977c640] Format matroska,webm probed with size=2048 and score=100
st:0 removing common factor 1000000 from timebase
[matroska,webm @ 0x977c640] File position before avformat_find_stream_info() is 450
[matroska,webm @ 0x977c640] All info found
[matroska,webm @ 0x977c640] File position after avformat_find_stream_info() is 36336
Input #0, matroska,webm, from 'out_mp4-webm.webm':
  Duration: 00:00:10.40, start: 0.000000, bitrate: 212 kb/s
    Stream #0:0, 1, 1/1000: Video: vp8, yuv420p, 720x576, 1/1000, SAR 212:199 DAR 265:199, 25 fps, 25 tbr, 1k tbn, 1k tbc (default)
[vp8 @ 0x9782d80] detected 2 logical cores
[STREAM]
index=0
codec_name=vp8
codec_long_name=On2 VP8
profile=unknown
codec_type=video
codec_time_base=1/1000
codec_tag_string=[0][0][0][0]
codec_tag=0x0000
width=720
height=576
has_b_frames=0
sample_aspect_ratio=212:199
display_aspect_ratio=265:199
pix_fmt=yuv420p
level=-99
timecode=N/A
id=N/A
r_frame_rate=25/1
avg_frame_rate=25/1
time_base=1/1000
start_pts=0
start_time=0.000000
duration_ts=N/A
duration=N/A
bit_rate=N/A
nb_frames=N/A
nb_read_frames=N/A
nb_read_packets=N/A
[/STREAM]
[FORMAT]
filename=out_mp4-webm.webm
nb_streams=1
format_name=matroska,webm
format_long_name=Matroska / WebM
start_time=0.000000
duration=10.400000
size=276619
bit_rate=212783
[/FORMAT]
[AVIOContext @ 0x9784c00] Statistics: 65536 bytes read, 0 seeks