Hi Jasper, Jasper Leemans wrote: > ---------------------------------------- > >> Date: Tue, 15 Apr 2008 11:23:26 -0400 >> From: [EMAIL PROTECTED] >> To: [email protected] >> Subject: Re: [libav-user] quality of encoding >> >> Jasper Leemans a écrit : >> >>> Hi all, >>> >>> I`m encoding raw frames to an mpeg1 stream and I`m just wondering, >>> is there a way to raise the quality, for example through the codec context >>> >>> c->quality = ... >>> >>> or lower the compression ratio. >>> >>> I can`t find anything similar in the c example code. >>> >>> wkr, >>> >>> Jasper >>> _________________________________________________________________ >>> Invite your mail contacts to join your friends list with Windows Live >>> Spaces. It's easy! >>> http://spaces.live.com/spacesapi.aspx?wx_action=create&wx_url=/friends.aspx&mkt=en-us >>> _______________________________________________ >>> libav-user mailing list >>> [email protected] >>> https://lists.mplayerhq.hu/mailman/listinfo/libav-user >>> >>> >> Hi >> The first thing you should check is the bitrate. I think that by default >> it's 200 kb/s. By increasing the bitrate you will for sure increase the >> quality. >> The compression ratio, by decreasing the gop you will add more key >> frames and therefore have better quality there too. >> >> I would like to have feedback on this. >> > > > I decreased the gop from 10 to 1, > I also changed the bitrate from 400kbit to 1000kbit, I notice these things: > > 1) when looking at the mpeg file info the bitrate went from 2600kbit to > 3000kbit/s, > so setting the bitrate with c->bitrate seems to have no real effect for me, > as I seem to have no real control over it, it ignores the bitrate I set. > > 2) the file got bigger but I see no noticeable visual improvement. >
Always change _one_ parameter at the time to see what it influences... So, you should have kept the GOP-size at 10 and only modified the bitrate. That should have shown a visual improvement, _except_ when the bitrate is too low and libavcodec will use a higher bitrate anyway. So, it also depends on the resolution of the video you are encoding: If you were encoding 720p video, 400kbit would be way too low and changing it wouldn't change much, as libavcodec would have probably used something higher then 400kbit in the first run anyway. And, I have to disagree with the statement that decreasing the GOP increases the quality. Especially the way you are using it now. You've (almost) turned your MPEG encoder into an MJPEG encoder which will decrease the compression ratio, and therefore, for a certain fixed bitrate you'll get less quality. With friendly regards, Takis _______________________________________________ libav-user mailing list [email protected] https://lists.mplayerhq.hu/mailman/listinfo/libav-user
