[FFmpeg-user] use q:v and maxrate

[YIRAN LI]

Hi guys,

I'm encoding videos target a max average bitrate and want to achieve good
encoding quality.

When I use

ffmpeg.exe -i a.mp4 -c:v mpeg4  -profile:v 15 -vtag DIVX -bufsize 3080000
 -maxrate 8000000 -bt 8000000  -an   a.avi (so that maxbitrate will be
8000kbps), in this case I get a.avi with 246kbps while the input is
727kbps. But the video quality is not as good as input.

Then I added -q:v 5 into above command, the result avi has a bitrate of
1029kbps so the quality is much better than the first one.

So my questions are:
1. for mpeg4 encoder, what qscale value is good enough to keep same quality
as input?
2. if -q:v, -maxrate -bt are used together,  no matter what qscale value
specified, bitrate will be guaranteed to be below maxrate?

Thanks