[Libav-user] qscale for vorbis encoder

YIRAN LI mrfun.china at gmail.com
Mon May 20 02:11:16 CEST 2013

Hi Guys,

I'm trying encoding ogg video with native experimental vorbis encoder.
While documentation here says the max qscale is 10 for vorbis audio, and
default is 6, http://ffmpeg.org/trac/ffmpeg/wiki/TheoraVorbisEncodingGuide

But I found that even if I pass 150 to -qscale:a I still can get files with
larger size than -qscale:10 (I keep same qscale for video, so I assume the
size increment is caused by audio part).

and the code fragment for vorbis quality is here

    avccontext->bit_rate = 0;
    if (avccontext->flags & CODEC_FLAG_QSCALE)
        venc->quality = avccontext->global_quality / (float)FF_QP2LAMBDA;
        venc->quality = 8;
    venc->quality *= venc->quality;

So could anyone tell me what's the maximum value I can set
AVCodecCtx->global_quality for Vorbis encoder?

Great thanks!
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