x264enc - changing the quality

[David Jaggard]

The quantizer value is only application if pass=4 or 5. I use 5 rather than
4 (I can't remember why but I know there is a good reason for it)

Anyway, if you set pass to 5, quantizer will make a difference.

On 7 December 2015 at 12:39, Ian Davidson <id012c3076 at blueyonder.co.uk>
wrote:

> My *real *application records live video and uses x264enc to encode it.
> The compression is 'a bit too aggressive' for my liking.
>
> I have written a program to convert a short video using x264enc to encode
> it so that I can compare the result using different levels of compression –
> (both video quality and file size).
>
> I have read elsewhere that “The range of the quantizer scale is 0-51:
> where 0 is lossless, 23 is default, and 51 is worst possible. A lower value
> is a higher quality and a subjectively sane range is 18-28. Consider 18 to
> be visually lossless or nearly so” and that “increasing the CRF value +6 is
> roughly half the bitrate while -6 is roughly twice the bitrate ”.
>
> I notice from gst-inspect that the x264enc plugin has a property
> “quantizer” (Constant quantizer or quality to apply … Unsigned integer.
> Range: 1-50 Default:21)
>
> I converted a 4 minute video using the default settings and the output
> file size was 31.4 MiB.
>
> I then changed the value of the quantizer using this line
>
> g_object_set (G_OBJECT (videnc), "quantizer", 18, NULL);
>
> and ran the program again. This time the file size was 31.4 MiB – so no
> change. I would have expected the file to be somewhat larger.
>
> So,
>
>    -
>
>    did I not actually change the property (I did not see any indication
>    that the line had failed)
>    -
>
>    should I have changed something else (as well)
>    -
>
>    should I have done it differently
>    -
>
>    does x264enc ignore that property
>
>
>
>
> _______________________________________________
> gstreamer-devel mailing list
> gstreamer-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freedesktop.org/archives/gstreamer-devel/attachments/20151207/23131420/attachment.html>