「1パス」として、vorbis、libvpxを含むビルドで次のように機能します...
2 パス libvpx のヒントについては、こちらを参照してください
rob@ Pictures$ ffmpeg -y -i me939371029.mp4 -r 30 out3.webm
ffmpeg version git-2012-08-29-85c8303 Copyright (c) 2000-2012 the FFmpeg developers
built on Aug 29 2012 08:59:14 with gcc 4.6 (Ubuntu/Linaro 4.6.3-1ubuntu5)
configuration: --enable-gpl --enable-libfaac --enable-libfdk-aac --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-librtmp --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-nonfree --enable-version3
libavutil 51. 70.100 / 51. 70.100
libavcodec 54. 54.100 / 54. 54.100
libavformat 54. 25.104 / 54. 25.104
libavdevice 54. 2.100 / 54. 2.100
libavfilter 3. 14.100 / 3. 14.100
libswscale 2. 1.101 / 2. 1.101
libswresample 0. 15.100 / 0. 15.100
libpostproc 52. 0.100 / 52. 0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'me939371029.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf54.22.100
Duration: 00:00:08.01, start: 0.000000, bitrate: 343 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuvj420p, 1296x972 [SAR 1:1 DAR 4:3], 316 kb/s, 0.57 fps, 0.50 tbr, 1 tbn, 1 tbc
Metadata:
handler_name : VideoHandler
Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 44100 Hz, mono, s16, 64 kb/s
Metadata:
handler_name : SoundHandler
[libvpx @ 0x1e7f500] v1.1.0
Output #0, webm, to 'out3.webm':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf54.25.104
Stream #0:0(und): Video: vp8, yuv420p, 1296x972 [SAR 1:1 DAR 4:3], q=-1--1, 200 kb/s, 1k tbn, 30 tbc
Metadata:
handler_name : VideoHandler
Stream #0:1(eng): Audio: vorbis, 44100 Hz, mono, flt
Metadata:
handler_name : SoundHandler
Stream mapping:
Stream #0:0 -> #0:0 (h264 -> libvpx)
Stream #0:1 -> #0:1 (aac -> libvorbis)
Press [q] to stop, [?] for help
[libvorbis @ 0x1e67060] Que input is backward in time
frame= 4 fps=0.0 q=0.0 Lsize= 122kB time=00:00:07.99 bitrate= 124.6kbits/s
video:51kB audio:63kB subtitle:0 global headers:3kB muxing overhead 3.241658%