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

[Tim Hiles]

I first sent this message as a non-subscriber and didn't receive word back
but the more I thought about it, I came to the decision that being on this
list I'm sure will definitely be useful as time progresses so I'm now an
official subscriber.. and on to my question...


On Sat, Oct 5, 2013 at 8:36 PM,  wrote:

> 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
>