[x264-devel] Degrade video quality by time

[Alex S]

Thanks for your information!
However, it is still degraded quality by time (but in different effect and
VBV overflow more).

Is there anyway that bits is overallocated constant overtime (mean, at low
bitrate, quality can be low but does not degrade by time)?


On Thu, Oct 27, 2011 at 10:11 AM, Alex Jurkiewicz <alex at jurkiewi.cz> wrote:

> You must specify a bufsize for VBV encoding to work. More info:
> http://mewiki.project357.com/wiki/X264_Encoding_Suggestions#VBV_Encoding
>
> Single pass bitrate-based ratecontrol doesn't work so well, because
> the ratecontrol algorithm has no information about the complexity of
> future scenes. It often overallocates bits at the start and has to
> underallocate later on.
>
> A common recommendation is to use CRF-based ratecontrol to pick a
> 'target quality' and VBV settings to constrain the maximum bitrate to
> below your maximum pipe size. This will use the lowest bitrate
> required to achieve the given CRF value, capped given the VBV
> settings.
>
> Try these options: rc_method=crf, crf=23, vbv_bufsize=164,
> vbv_maxrate=164. Don't specify bitrate.
>
> Also, at such a low bitrate you might want to consider intra-refresh
> as well, which will make the size of each frame more consistent. This
> can improve streaming performance when you have small VBV buffers.
>
> Alex
>
> On Mon, Oct 24, 2011 at 2:23 PM, Alex S <flashsupporter at gmail.com> wrote:
> > I am using x264 in ABR and CBR mode. However, the quality is degraded by
> > time.
> > If I use CQP ratecontrol method, the quality is acceptable at bitrate
> > 160kbps. However, with the same bitrate (or even higher) in ABR/CBR mode,
> > video quality is degraded by time and unacceptable.
> > Here is context setting in my code:
> > x264_param_default_preset(&param, "veryfast", "zerolatency");
> > x264_param_apply_profile(&param, "main");
> > param.i_threads = 1;
> > param.i_width = width;
> > param.i_height = height;
> > param.i_fps_num = fps;
> > param.i_fps_den = 1;
> > param.i_keyint_max = fps * 2
> > param.b_intra_refresh = 0;
> > param.rc.i_bitrate = 164     ;
> > param.rc.i_vbv_max_bitrate = 164;
> > param.rc.i_rc_method = X264_RC_ABR;
> > param.b_repeat_headers = 1;
> > param.b_annexb = 1;
> > Could anybody help me to modify or add other setting parameters to solve
> the
> > problem?
> > Thank you!
> > Alex
> >
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> >
> >
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