[Libav-user] How to convert "-q:v 1" to API form

[Arthur Muller]

Carl,

Thanks for the quick reply.

I made the change you suggested, but the quality is still not what I need. My images are all technical, containing labels, numbers, etc., and I can't really read them. Do I also need to set 

flags |= CODEC_FLAG_QSCALE

I ask because the size of the file changed significantly when this flag is turned on - although the quality didn't change much.

Thanks.

-Arthur

-----Original Message-----
From: Libav-user [mailto:libav-user-bounces at ffmpeg.org] On Behalf Of Carl Eugen Hoyos
Sent: Thursday, January 28, 2016 2:21 PM
To: libav-user at ffmpeg.org
Subject: Re: [Libav-user] How to convert "-q:v 1" to API form

Arthur Muller <muller at ...> writes:

> Using the API version of ffmpeg I’ve managed to generate the mp4 file 
> by first converting the png files to yuv format. That was not a 
> problem. But I haven’t figured out what I have to do in my code to 
> mimic the behavior of “-q:v 1” to get the better quality?

(Old MEncoder documentation suggested not to use a value smaller than "2".)

You have to set AVCodecContext->global_quality but you have to multiply the qscale:
global_quality = qscale * FF_QP2LAMBDA

Carl Eugen
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