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Thread: Help in understanding a couple of ffmpeg warnings

  1. #1
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    Help in understanding a couple of ffmpeg warnings

    Hello,

    Can anyone help me to understand why I'm getting the following warnings, please? What am I supposed to change in the command I fire?

    Code:
    nice ffmpeg -i "source.mkv" -map 0:0 -s 640x272 -f ogg -vcodec libtheora -r 23.98 -b:v 1200k -acodec libvorbis -ac 6 -ar 48000 -b:a 192k -vol 300 -map 0:1 -async 1 -pass 2 -passlogfile "pass" "target.ogv"
    
    ffmpeg version git-2012-03-05-1007a80 Copyright (c) 2000-2012 the FFmpeg developers
      built on Mar  5 2012 09:40:09 with gcc 4.6.1
      configuration: --enable-gpl --enable-libfaac --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libtheora --enable-libvorbis --enable-libx264 --enable-nonfree --enable-version3 --enable-x11grab --enable-libxvid --enable-libvpx
      libavutil      51. 41.100 / 51. 41.100
      libavcodec     54.  8.100 / 54.  8.100
      libavformat    54.  2.100 / 54.  2.100
      libavdevice    53.  4.100 / 53.  4.100
      libavfilter     2. 63.100 /  2. 63.100
      libswscale      2.  1.100 /  2.  1.100
      libswresample   0.  7.100 /  0.  7.100
      libpostproc    52.  0.100 / 52.  0.100
    Input #0, matroska,webm, from 'source.mkv':
      Metadata:
        title           : title [HDTV,H.264,AC3] - THOR
      Duration: 01:55:05.35, start: 0.000000, bitrate: 5428 kb/s
        Stream #0:0(eng): Video: h264 (High), yuv420p, 1280x544, SAR 1:1 DAR 40:17, 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
        Metadata:
          title           : title
        Stream #0:1(eng): Audio: ac3, 48000 Hz, stereo, s16, 384 kb/s (default)
        Metadata:
          title           : AC3 2.0
        Stream #0:2(eng): Subtitle: ssa (default)
        Metadata:
          title           : English ***
        Stream #0:3: Attachment: ttf
        Metadata:
          filename        : TCCEB.TTF
          mimetype        : application/x-truetype-font
        Stream #0:4: Attachment: ttf
        Metadata:
          filename        : TCCEB.TTF
          mimetype        : application/x-truetype-font
    [buffer @ 0xaaee280] w:1280 h:544 pixfmt:yuv420p tb:1/1000000 sar:1/1 sws_param:
    [scale @ 0xaae4880] w:1280 h:544 fmt:yuv420p -> w:640 h:272 fmt:yuv420p flags:0x4
    Incompatible sample format 's16' for codec 'libvorbis', auto-selecting format 'flt'
    [libvorbis @ 0xaae84c0] No channel layout specified. The encoder will use Vorbis channel layout for 6 channels.
    Output #0, ogg, to 'target.ogv':
      Metadata:
        title           : title
        comment         : comment
        date            : date
        encoder         : Lavf54.2.100
        Stream #0:0(eng): Video: theora, yuv420p, 640x272 [SAR 1:1 DAR 40:17], q=2-31, pass 2, 1200 kb/s, 23.98 tbn, 23.98 tbc (default)
        Metadata:
          title           : title
        Stream #0:1(eng): Audio: vorbis, 48000 Hz, 6 channels, flt, 192 kb/s (default)
        Metadata:
          title           : AC3 2.0
    Stream mapping:
      Stream #0:0 -> #0:0 (h264 -> libtheora)
      Stream #0:1 -> #0:1 (ac3 -> libvorbis)
    Thank you in advance!

  2. #2
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    Re: Help in understanding a couple of ffmpeg warnings

    Do you really want 6 channel sound for your output file?
    You think that's air you're breathing now?

  3. #3
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    Re: Help in understanding a couple of ffmpeg warnings

    Thank you, setting -ac 2 will remove the second warning.
    Still remains the first one:

    Incompatible sample format 's16' for codec 'libvorbis', auto-selecting format 'flt'

  4. #4
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    Re: Help in understanding a couple of ffmpeg warnings

    You can ignore that. It's just telling you that it's converting to a different audio sample format.

  5. #5
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    Re: Help in understanding a couple of ffmpeg warnings

    Indeed you could safely ignore both warnings (and even manually map the 6 channels if you were really keen). If the sample format warning really bothers you you could bypass FFmpeg's auto selection and add something like the following to use floating point in your commandline:

    Code:
    -sample_fmt flt
    but this is not really necessary. Most of the details here:

    Code:
    andrew@skamandros~$ ffmpeg -h 2>/dev/null | grep sample_fmt
    -sample_fmts        show available audio sample formats
    -sample_fmt format  set sample format
    -request_sample_fmt <int>   .D.A. sample format audio decoders should prefer
    -in_sample_fmt     <int>   ...A. Input Sample Format
    -out_sample_fmt    <int>   ...A. Output Sample Format
    -internal_sample_fmt <int>   ...A. Internal Sample Format
    Lots of room for small adjustments in FFmpeg .
    You think that's air you're breathing now?

  6. #6
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    Re: Help in understanding a couple of ffmpeg warnings

    Thank you all guys for your nice and kind explanation.

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