Francesco Scaglione

Per estrarre la traccia suono da un video HD postato in YouTube (e scaricato con youtube-dl), niente di più facile:

- prima si analizza il video

francesco@serverHP:~$ ffmpeg -i Halcyon.mp4 
ffmpeg version 0.7.13, Copyright (c) 2000-2011 the FFmpeg developers
  built on Jun 13 2012 14:14:09 with gcc 4.4.5
  configuration: --enable-libdc1394 --prefix=/usr --extra-cflags='-Wall -g ' --cc='ccache cc' --enable-shared --enable-libmp3lame --enable-gpl --enable-libvorbis --enable-pthreads --enable-libfaac --enable-libxvid --enable-postproc --enable-x11grab --enable-libgsm --enable-libtheora --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libx264 --enable-libspeex --enable-nonfree --disable-stripping --enable-avfilter --enable-libdirac --disable-decoder=libdirac --enable-libfreetype --enable-libschroedinger --disable-encoder=libschroedinger --enable-version3 --enable-libopenjpeg --enable-libvpx --enable-librtmp --extra-libs=-lgcrypt --disable-altivec --disable-armv5te --disable-armv6 --disable-vis
  libavutil    50. 43. 0 / 50. 43. 0
  libavcodec   52.123. 0 / 52.123. 0
  libavformat  52.111. 0 / 52.111. 0
  libavdevice  52.  5. 0 / 52.  5. 0
  libavfilter   1. 80. 0 /  1. 80. 0
  libswscale    0. 14. 1 /  0. 14. 1
  libpostproc  51.  2. 0 / 51.  2. 0

Seems stream 0 codec frame rate differs from container frame rate: 59.83 (29917/500) -> 29.92 (359/12)
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'Halcyon.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    creation_time   : 2011-06-18 17:54:45
  Duration: 00:11:10.37, start: 0.000000, bitrate: 1636 kb/s
    Stream #0.0(und): Video: h264 (High), yuv420p, 1440x1080, 1478 kb/s, 29.97 fps, 29.92 tbr, 1k tbn, 59.83 tbc
    Metadata:
      creation_time   : 1970-01-01 00:00:00
    Stream #0.1(und): Audio: aac, 44100 Hz, stereo, s16, 151 kb/s
    Metadata:
      creation_time   : 2011-06-18 17:54:47
At least one output file must be specified

- e poi si estrae la traccia Flac (questo vuol dire aac in Stream #0.1, credo):

francesco@serverHP:~$ ffmpeg -i Halcyon.mp4 Halcyon.flac
ffmpeg version 0.7.13, Copyright (c) 2000-2011 the FFmpeg developers
  built on Jun 13 2012 14:14:09 with gcc 4.4.5
  configuration: --enable-libdc1394 --prefix=/usr --extra-cflags='-Wall -g ' --cc='ccache cc' --enable-shared --enable-libmp3lame --enable-gpl --enable-libvorbis --enable-pthreads --enable-libfaac --enable-libxvid --enable-postproc --enable-x11grab --enable-libgsm --enable-libtheora --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libx264 --enable-libspeex --enable-nonfree --disable-stripping --enable-avfilter --enable-libdirac --disable-decoder=libdirac --enable-libfreetype --enable-libschroedinger --disable-encoder=libschroedinger --enable-version3 --enable-libopenjpeg --enable-libvpx --enable-librtmp --extra-libs=-lgcrypt --disable-altivec --disable-armv5te --disable-armv6 --disable-vis
  libavutil    50. 43. 0 / 50. 43. 0
  libavcodec   52.123. 0 / 52.123. 0
  libavformat  52.111. 0 / 52.111. 0
  libavdevice  52.  5. 0 / 52.  5. 0
  libavfilter   1. 80. 0 /  1. 80. 0
  libswscale    0. 14. 1 /  0. 14. 1
  libpostproc  51.  2. 0 / 51.  2. 0

Seems stream 0 codec frame rate differs from container frame rate: 59.83 (29917/500) -> 29.92 (359/12)
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'Halcyon.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    creation_time   : 2011-06-18 17:54:45
  Duration: 00:11:10.37, start: 0.000000, bitrate: 1636 kb/s
    Stream #0.0(und): Video: h264 (High), yuv420p, 1440x1080, 1478 kb/s, 29.97 fps, 29.92 tbr, 1k tbn, 59.83 tbc
    Metadata:
      creation_time   : 1970-01-01 00:00:00
    Stream #0.1(und): Audio: aac, 44100 Hz, stereo, s16, 151 kb/s
    Metadata:
      creation_time   : 2011-06-18 17:54:47
Output #0, flac, to 'Halcyon.flac':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    creation_time   : 2011-06-18 17:54:45
    encoder         : Lavf52.111.0
    Stream #0.0(und): Audio: flac, 44100 Hz, stereo, s16, 64 kb/s
    Metadata:
      creation_time   : 2011-06-18 17:54:47
Stream mapping:
  Stream #0.1 -> #0.0
Press [q] to stop, [?] for help
size=   71337kB time=00:11:10.40 bitrate= 871.7kbits/s    
video:0kB audio:71329kB global headers:0kB muxing overhead 0.011443%

In questo modo non abbiamo perso nulla della qualità originaria. Certo, i files che risultano non sono proprio leggeri:

francesco@serverHP:~$ ll | grep Halcyon
-rw-r--r--  1 francesco francesco  70M  8 juil. 15:38 Halcyon.flac
-rw-r--r--  1 francesco francesco 131M 19 juin   2011 Halcyon.mp4
-rw-r--r--  1 francesco francesco  60M  8 juil. 15:39 Halcyon_on_on.flac
-rw-r--r--  1 francesco francesco 145M 26 févr.  2009 Halcyon_on_on.mp4