[FFmpeg-devel] Path for minor problems related to ffmpeg help text and x264 configuration

Francesco Cosoleto cosoleto
Fri Sep 26 17:38:33 CEST 2008

2008/9/25 Robert Swain <robert.swain at gmail.com>:
 >>> +    /* char *res = (char *) x264_param2string(&x4->params, 0);
 >>> +    av_log(avctx, AV_LOG_INFO, "Options: %s", res);
 >>> +    x264_free(res); */
 > > Why libx264 doesn't already set all those values to 0 by default?
 > Why is this commented code being added?

That is only for debug purpose. However, I don't see a way for users to 
check libx264 parameters. Preset parameters in current release aren't 
checked, if you wrong writing "cfr" instead of "crf", "me" instead of 
"me_method", or also "i_qfactor=1.40" instead of "i_qfactor=0.71" you 
cannot see it. If I am not wrong libx264 writes setting used into H264 
stream (as returned by x264_param2string()), but FFmpeg strips these 
extra data. So, how to see these parameters before or after the file is 

 > This applies to all the above: I think !!(flag & FLAG) would be
 > preferred to the ternary stuff. And regardless, are they actually
 > needed? Or is this the cosmetic stuff you mention?

Of course If you don't use x264_param2string() the ternary stuff is 

 >>> +    // x4->params.analyse.b_ssim = 0;
 >>> +    x4->params.analyse.b_psnr = avctx->flags & CODEC_FLAG_PSNR ?
 >>> 1 : 0;

I am suggesting to add a SSIM flag parameter, else SSIM is enabled by 
default. Is that a good idea? It should slightly reduce encoding time.

Francesco Cosoleto | http://cosoleto.free.fr

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