[Chimera-users] movie quality

Tom Goddard goddard at sonic.net
Wed Jan 4 11:57:06 PST 2012

Hi Ernesto,

   The "bitrate" option to the movie command creates a constant bit rate 
encoding while the "qscale" option creates a variable bit rate 
encoding.  Generally a variable bit rate is better because it allows the 
video to use a high bit rate when there is lots of motion and low bit 
rate when there is little motion.  This can produce the highest quality 
with the smallest file size.  So I recommend using the qscale option.  
The qscale values range from 1 (highest quality) to 31 (lowest quality) 
and the Chimera default if no qscale or bitrate is given is qscale 8.  I 
think 8 gives a medium quality in most cases.  It may depend on the 
video size in pixels.  If you specify qscale, then bitrate is ignored.  
My impression is that qscale 3 or less gives very high quality.  Of 
course higher quality means bigger file size.  So the quality choice 
depends on how you will use your movie.  If it is for viewing on the web 
you may need to use a lower quality and smaller window size because the 
bandwidth for your viewer may not be high enough, or they don't want to 
wait for a large file to download.  Likewise if you are using it as 
supplementary material for a paper you might need to go with lower 
quality or smaller window size so the download is not too slow.  If I am 
showing a video during a talk I sometimes use qscale 1 (very highest 
quality) and large video size because my laptop can handle the very high 
bit rate.  I have the impression that PowerPoint tends to choke playing 
large high bitrate videos but why PowerPoint decides to refuse to play a 
video is always a mystery.  You just have to test it to know.


> Hi Tom,
> Thank you so much for your quick reply. A 5000kb bitrate sounds 
> reasonable to you? Which value would you use for a medium-high quality 
> movie?
> Thanks again for your help and congratulations for the really good job 
> that you're doing with chimera.
> Ernesto.

> Hi Ernesto,
>   I see that Chimera daily builds are incorrectly giving the option 
> "-qscale 8" to ffmpeg, the program included in Chimera that does the 
> movie encoding.  The "-qscale 8" conflicts and apparently overrides 
> the "-b 5000kb" bit rate setting you requested.  Both Chimera 1.5.3 
> and daily builds use qscale 8 which is variable bit rate encoding if 
> you do not specify bitrate.  Recent changes to Chimera movie defaults 
> broke the movie quality handling.  I have fixed it.  The fix will be 
> in tonight's daily build, dated Jan 5 on the download page
> http://www.cgl.ucsf.edu/chimera/download.html#daily
> Thanks for identifying the problem.
>     Tom
>> Hi everyone,
>> I've made some movies using the current Chimera alpha version (alpha 
>> version 1.6 build 35109, 2011-12-24) in an ubuntu 10.04 laptop. I've 
>> noticed that the quality of the movies is worse that in the version 
>> 1.5.3, and I have generated the movies using the same chimera session 
>> and the same script. I've seen this for at least avi and mp4 formats.
>> The movie options I'm using in the script are:
>> /movie record supersample 3
>> movie encode output movie.avi bitrate 5000 framerate 25 mformat avi/
>> Does anybody know why the quality is worse in the newer Chimera version?
>> Thanks in advance,
>> Ernesto.
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