Without -deinterlace

$ ./ffmpeg -y -i redcliff.webm -threads 8 -f webm -vcodec libvpx -g 120 -level 216 -profile 0 -qmax 42 -qmin 10 -rc_buf_aggressivity 0.95 -vb 2M -acodec libvorbis -aq 70 -ac 2 transcoded.webm
ffmpeg version N-41027-ge02e58f Copyright (c) 2000-2012 the FFmpeg developers
  built on May 25 2012 13:09:41 with gcc 4.6.3
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-runtime-cpudetect --enable-avisynth --enable-bzlib --enable-frei0r --enable-libass --enable-libcelt --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libfreetype --enable-libgsm --enable-libmp3lame --enable-libnut --enable-libopenjpeg --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libutvideo --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enable-libxvid --enable-zlib
  libavutil      51. 54.100 / 51. 54.100
  libavcodec     54. 23.100 / 54. 23.100
  libavformat    54.  6.100 / 54.  6.100
  libavdevice    54.  0.100 / 54.  0.100
  libavfilter     2. 77.100 /  2. 77.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0. 15.100 /  0. 15.100
  libpostproc    52.  0.100 / 52.  0.100
Input #0, matroska,webm, from 'redcliff.webm':
  Duration: 00:02:14.09, start: 0.000000, bitrate: 733 kb/s
    Stream #0:0(eng): Video: vp8, yuv420p, 450x256, SAR 1:1 DAR 225:128, 30 fps, 30 tbr, 1k tbn, 1k tbc (default)
    Metadata:
      title           : VP8 video stream
    Stream #0:1(eng): Audio: vorbis, 22050 Hz, stereo, s16 (default)
Please use -profile:a or -profile:v, -profile is ambiguous
[buffer @ 0000000003c602a0] w:450 h:256 pixfmt:yuv420p tb:1/1000 sar:1/1 sws_param:flags=2
[buffersink @ 0000000003c603c0] No opaque field provided
[aformat @ 00000000002ff840] auto-inserting filter 'auto-inserted resampler 0' between the filter 'src' and the filter 'aformat'
[aresample @ 00000000002ffc40] chl:stereo fmt:s16 r:22050Hz -> chl:stereo fmt:flt r:22050Hz
[libvpx @ 0000000003c5f4e0] v1.0.0
Output #0, webm, to 'transcoded.webm':
  Metadata:
    encoder         : Lavf54.6.100
    Stream #0:0(eng): Video: vp8, yuv420p, 450x256 [SAR 1:1 DAR 225:128], q=10-42, 2000 kb/s, 1k tbn, 30 tbc (default)
    Metadata:
      title           : VP8 video stream
    Stream #0:1(eng): Audio: vorbis, 22050 Hz, stereo, flt (default)
Stream mapping:
  Stream #0:0 -> #0:0 (vp8 -> libvpx)
  Stream #0:1 -> #0:1 (vorbis -> libvorbis)
Press [q] to stop, [?] for help
[libvorbis @ 0000000003c60660] Que input is backward in time
frame= 3992 fps=216 q=0.0 Lsize=   18084kB time=00:02:13.06 bitrate=1113.3kbits/s
video:15736kB audio:2268kB global headers:3kB muxing overhead 0.423021%

$ ./ffmpeg.exe -i transcoded.webm -ss 134.5 -vframes 1 test.png
ffmpeg version N-41027-ge02e58f Copyright (c) 2000-2012 the FFmpeg developers
  built on May 25 2012 13:09:41 with gcc 4.6.3
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-runtime-cpudetect --enable-avisynth --enable-bzlib --enable-frei0r --enable-libass --enable-libcelt --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libfreetype --enable-libgsm --enable-libmp3lame --enable-libnut --enable-libopenjpeg --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libutvideo --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enable-libxvid --enable-zlib
  libavutil      51. 54.100 / 51. 54.100
  libavcodec     54. 23.100 / 54. 23.100
  libavformat    54.  6.100 / 54.  6.100
  libavdevice    54.  0.100 / 54.  0.100
  libavfilter     2. 77.100 /  2. 77.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0. 15.100 /  0. 15.100
  libpostproc    52.  0.100 / 52.  0.100
Input #0, matroska,webm, from 'transcoded.webm':
  Duration: 00:02:14.59, start: 0.000000, bitrate: 1100 kb/s
    Stream #0:0(eng): Video: vp8, yuv420p, 450x256, SAR 1:1 DAR 225:128, 30 fps, 30 tbr, 1k tbn, 1k tbc (default)
    Metadata:
      title           : VP8 video stream
    Stream #0:1(eng): Audio: vorbis, 22050 Hz, stereo, s16 (default)
[buffer @ 0000000000332860] w:450 h:256 pixfmt:yuv420p tb:1/1000 sar:1/1 sws_param:flags=2
[buffersink @ 0000000000332b40] No opaque field provided
[format @ 0000000000333300] auto-inserting filter 'auto-inserted scaler 0' between the filter 'src' and the filter 'format'
[scale @ 00000000003336a0] w:450 h:256 fmt:yuv420p sar:1/1 -> w:450 h:256 fmt:rgb24 sar:1/1 flags:0x4
Output #0, image2, to 'test.png':
  Metadata:
    encoder         : Lavf54.6.100
    Stream #0:0(eng): Video: png, rgb24, 450x256 [SAR 1:1 DAR 225:128], q=2-31, 200 kb/s, 90k tbn, 30 tbc (default)
    Metadata:
      title           : VP8 video stream
Stream mapping:
  Stream #0:0 -> #0:0 (vp8 -> png)
Press [q] to stop, [?] for help
frame=    0 fps=0.0 q=0.0 Lsize=       0kB time=00:00:00.00 bitrate=   0.0kbits/s
video:0kB audio:0kB global headers:0kB muxing overhead nan%
Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)

$ ./ffmpeg.exe -i transcoded.webm -ss 134.5 -vframes 1 test.png
ffmpeg version N-41027-ge02e58f Copyright (c) 2000-2012 the FFmpeg developers
  built on May 25 2012 13:09:41 with gcc 4.6.3
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-runtime-cpudetect --enable-avisynth --enable-bzlib --enable-frei0r --enable-libass --enable-libcelt --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libfreetype --enable-libgsm --enable-libmp3lame --enable-libnut --enable-libopenjpeg --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libutvideo --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enable-libxvid --enable-zlib
  libavutil      51. 54.100 / 51. 54.100
  libavcodec     54. 23.100 / 54. 23.100
  libavformat    54.  6.100 / 54.  6.100
  libavdevice    54.  0.100 / 54.  0.100
  libavfilter     2. 77.100 /  2. 77.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0. 15.100 /  0. 15.100
  libpostproc    52.  0.100 / 52.  0.100
Input #0, matroska,webm, from 'transcoded.webm':
  Duration: 00:02:14.59, start: 0.000000, bitrate: 1100 kb/s
    Stream #0:0(eng): Video: vp8, yuv420p, 450x256, SAR 1:1 DAR 225:128, 30 fps, 30 tbr, 1k tbn, 1k tbc (default)
    Metadata:
      title           : VP8 video stream
    Stream #0:1(eng): Audio: vorbis, 22050 Hz, stereo, s16 (default)
[buffer @ 0000000001e42860] w:450 h:256 pixfmt:yuv420p tb:1/1000 sar:1/1 sws_param:flags=2
[buffersink @ 0000000001e42b40] No opaque field provided
[format @ 0000000001e43300] auto-inserting filter 'auto-inserted scaler 0' between the filter 'src' and the filter 'format'
[scale @ 0000000001e436a0] w:450 h:256 fmt:yuv420p sar:1/1 -> w:450 h:256 fmt:rgb24 sar:1/1 flags:0x4
Output #0, image2, to 'test.png':
  Metadata:
    encoder         : Lavf54.6.100
    Stream #0:0(eng): Video: png, rgb24, 450x256 [SAR 1:1 DAR 225:128], q=2-31, 200 kb/s, 90k tbn, 30 tbc (default)
    Metadata:
      title           : VP8 video stream
Stream mapping:
  Stream #0:0 -> #0:0 (vp8 -> png)
Press [q] to stop, [?] for help
frame=    0 fps=0.0 q=0.0 Lsize=       0kB time=00:00:00.00 bitrate=   0.0kbits/s
video:0kB audio:0kB global headers:0kB muxing overhead nan%
Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)