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Thread: A question about ffmpeg and qscale

  1. #1
    Join Date
    Feb 2013
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    4

    A question about ffmpeg and qscale

    I have been trying to get qscale to work in ffmpeg but I always get the same size of output file no matter what value I give for qscale. Is qscale codec dependent or maybe I am doing something wrong, my ffmpeg is ffmpeg version 0.8.6-6:0.8.6-0ubuntu0.12.10.1.

    The following is how I have been testing, the input file is flv but I have also used vob files for the input and always the same result.

    Code:
    ffmpeg -i input.flv -vcodec libx264 -qscale 1 -acodec ac3 -ac 2 -ar 48K -ab 224K -async 1 output.mkv
    In the above example a qscale of 1 and 10 produces identical output files in size and bitrate, I have assumed that increasing the qscale value should give a reduced bitrate in the output file, is my assumption correct.

  2. #2
    Join Date
    Dec 2006
    Beans
    7,312

    Re: A question about ffmpeg and qscale

    Rather than me talking about an area I understand poorly have a look here:

    https://ffmpeg.org/trac/ffmpeg/wiki/x264EncodingGuide

    where the details are explained.
    You think that's air you're breathing now?

  3. #3
    Join Date
    Sep 2006
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    3,713

    Re: A question about ffmpeg and qscale

    The encoder you're using, libx264, ignores "-qscale"; instead use "-crf" (note that the values will be different than typical "-qscale" usage) as shown in the link andrew.46 provided. If you must use "-qscale", then use a different encoder such as: mpeg1video, mpeg2video, mpeg4, mjpeg, msmpeg4v2, msmpeg4, h263, h263p, and flv (the encoder, not the container format).
    Last edited by FakeOutdoorsman; May 14th, 2013 at 03:20 AM.

  4. #4
    Join Date
    Feb 2013
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    4

    Re: A question about ffmpeg and qscale

    Thanks guys for pointing me in the right direction, I have some reading to do.

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