[x264-devel] Degrade video quality by time

[Alex Jurkiewicz]

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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