[FFmpeg-user] Stereo WMA to right / left mono WMA without reencoding

[Tim Hiles]

So.. been trying to figure out if this is possible but can't seem to find
this through google searches or in past ffmpeg list threads.  All i want to
do is split a stereo wma file into left and right mono files without
reencoding... i.e. no conversion to wav.  the reason is, I have all of
these wma recordings that are recorded on one side of a stereo file.  I'd
like to save some space by getting rid of the blank side. converting to wav
only creates a huge file, same goes when you convert to flac.. defeating
the purpose of all of this in the first place.



Here's what I have so far:

WS400104.WMA file that is 204,040 KB

command:

c:\ffmpeg\ffmpeg\bin\ffmpeg.exe -i WS400104.WMA -map_channel 0.0.1:0.1
-acodec copy out.wma

output:

ffmpeg version N-51683-g9dc88ac Copyright (c) 2000-2013 the FFmpeg
developers
  built on Apr  8 2013 21:19:21 with gcc 4.8.0 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads
--enable-avisynth --enable-bzlib --enable-fontconfi
g --enable-frei0r --enable-gnutls --enable-iconv --enable-libass
--enable-libbluray --enable-libcaca --enable-libfreetyp
e --enable-libgsm --enable-libilbc --enable-libmp3lame
--enable-libopencore-amrnb --enable-libopencore-amrwb --enable-li
bopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger
--enable-libsoxr --enable-libspeex --enable-libtheo
ra --enable-libtwolame --enable-libvo-aacenc --enable-libvo-amrwbenc
--enable-libvorbis --enable-libvpx --enable-libx264
 --enable-libxavs --enable-libxvid --enable-zlib
  libavutil      52. 25.100 / 52. 25.100
  libavcodec     55.  2.100 / 55.  2.100
  libavformat    55.  1.100 / 55.  1.100
  libavdevice    55.  0.100 / 55.  0.100
  libavfilter     3. 49.101 /  3. 49.101
  libswscale      2.  2.100 /  2.  2.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  2.100 / 52.  2.100
Guessed Channel Layout for  Input Stream #0.0 : stereo
Input #0, asf, from 'WS400104.WMA':
  Duration: 03:36:32.54, start: 0.000000, bitrate: 128 kb/s
    Stream #0:0: Audio: wmav2 (a[1][0][0] / 0x0161), 44100 Hz, stereo,
fltp, 128 kb/s
File 'out.wma' already exists. Overwrite ? [y/N] y
Output #0, asf, to 'out.wma':
  Metadata:
    WM/EncodingSettings: Lavf55.1.100
    Stream #0:0: Audio: wmav2 (a[1][0][0] / 0x0161), 44100 Hz, stereo, 128
kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
Press [q] to stop, [?] for help
size=  218588kB time=03:36:32.51 bitrate= 137.8kbits/s
video:0kB audio:203047kB subtitle:0 global headers:0kB muxing overhead
7.653751%

but as you see..  my output file is a stereo file.  So, I tried this:

command:

c:\ffmpeg\ffmpeg\bin\ffmpeg.exe -i WS400104.WMA -map_channel 0.0.1:0.1 -ac
1 out.wma

but got this:

output:

H:\asis\ansem2013>c:\ffmpeg\ffmpeg\bin\ffmpeg.exe -i WS400104.WMA
-map_channel 0.0.1:0.1 -ac 1 out.wma
ffmpeg version N-51683-g9dc88ac Copyright (c) 2000-2013 the FFmpeg
developers
  built on Apr  8 2013 21:19:21 with gcc 4.8.0 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads
--enable-avisynth --enable-bzlib --enable-fontconfi
g --enable-frei0r --enable-gnutls --enable-iconv --enable-libass
--enable-libbluray --enable-libcaca --enable-libfreetyp
e --enable-libgsm --enable-libilbc --enable-libmp3lame
--enable-libopencore-amrnb --enable-libopencore-amrwb --enable-li
bopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger
--enable-libsoxr --enable-libspeex --enable-libtheo
ra --enable-libtwolame --enable-libvo-aacenc --enable-libvo-amrwbenc
--enable-libvorbis --enable-libvpx --enable-libx264
 --enable-libxavs --enable-libxvid --enable-zlib
  libavutil      52. 25.100 / 52. 25.100
  libavcodec     55.  2.100 / 55.  2.100
  libavformat    55.  1.100 / 55.  1.100
  libavdevice    55.  0.100 / 55.  0.100
  libavfilter     3. 49.101 /  3. 49.101
  libswscale      2.  2.100 /  2.  2.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  2.100 / 52.  2.100
Guessed Channel Layout for  Input Stream #0.0 : stereo
Input #0, asf, from 'WS400104.WMA':
  Duration: 03:36:32.54, start: 0.000000, bitrate: 128 kb/s
    Stream #0:0: Audio: wmav2 (a[1][0][0] / 0x0161), 44100 Hz, stereo,
fltp, 128 kb/s
File 'out.wma' already exists. Overwrite ? [y/N] y
Output #0, asf, to 'out.wma':
  Metadata:
    WM/EncodingSettings: Lavf55.1.100
    Stream #0:0: Audio: wmav2 (a[1][0][0] / 0x0161), 44100 Hz, mono, fltp,
128 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (wmav2 -> wmav2)
Press [q] to stop, [?] for help
size=  218572kB time=03:36:32.51 bitrate= 137.8kbits/s
video:0kB audio:202999kB subtitle:0 global headers:0kB muxing overhead
7.671857%

which gives me a mono wma that is now bigger in size than the stereo wma I
had to start out with. and also.. my bitrate is different (ffmpeg default?)

Would love and appreciate your help.

Tim