Hi Adam May I ask why you went with 720x406 resolution?
I reproduced your good results with ffmepg, however with the following 2-pass commandline I was able to shave off an additional 9-10% filesize by collapsing the audio to mono (I also used 640x360 resolution but this tweak has only small impact on the filesize) $ ffmpeg -y -hide_banner -i 5HMMfiyszjo.mp4 -ac 1 -b:a 40k -c:v libx264 -profile:v baseline -level 3.0 -vf "scale=640x360" -r 15 -b:v 10k -maxrate 15k -bufsize 512k -pass 1 -f mp4 /dev/null && ffmpeg -y -hide_banner -i 5HMMfiyszjo.mp4 -ac 1 -b:a 40k -c:v libx264 -profile:v baseline -level 3.0 -vf "scale=640x360" -r 15 -b:v 10k -maxrate 15k -bufsize 512k -pass 2 -f mp4 5HMMfiyszjo.compress.mp4 Sean P.S. I'm living in NYC now On Tue, May 30, 2017 at 2:19 PM, Adam Holt <h...@laptop.org> wrote: > Can folks plz evaluate the quality of those videos on the left, compared > to the originals on the right? Note that he/we did not compress the audio > channel, which should remain in very high quality stereo for now. We've > begun by translating KA Lite's 8732 English videos, most all of which (I > believe!) originate from Khan Academy itself -- making tight compression > attractive in several communities that use SD Cards rather than hard disk > drives for their digital libraries (despite the tradeoffs you will see > below!) > > Constructive criticism would be really great, as this is progressing fast, > and QA is *always* the hardest part. e.g. What specific flaws do you see > in any video on the LEFT, that are simply unacceptable?? Some lossiness > (degradation) cannot be avoided of course! Still, teacher's "fieldback" > would be especially interesting here (even as new many usage patterns are > evolving on small/mobile screens, outside of schools especially!!) as I > noticed widely varying compression rate across the board, across the 1st 10 > videos compressed he compressed here: > > 1. 5HMMfiyszjo.mp4 > <http://unleashkids.org/%7Eholt/10new/5HMMfiyszjo.mp4> is 38.7% of > 6.9M 5HMMfiyszjo.mp4 > <http://unleashkids.org/%7Eholt/10old/5HMMfiyszjo.mp4> > 2. 91wF7Ef_k8Y.mp4 > <http://unleashkids.org/%7Eholt/10new/91wF7Ef_k8Y.mp4> is 26.6% of 17M > 91wF7Ef_k8Y.mp4 <http://unleashkids.org/%7Eholt/10old/91wF7Ef_k8Y.mp4> > 3. DNoDJlB0ygU.mp4 > <http://unleashkids.org/%7Eholt/10new/DNoDJlB0ygU.mp4> is 54.2% of > 2.8M DNoDJlB0ygU.mp4 > <http://unleashkids.org/%7Eholt/10old/DNoDJlB0ygU.mp4> > 4. KNklNvGof8o.mp4 > <http://unleashkids.org/%7Eholt/10new/KNklNvGof8o.mp4> is 29.0% of 15M > KNklNvGof8o.mp4 <http://unleashkids.org/%7Eholt/10old/KNklNvGof8o.mp4> > 5. LDyMYyiAsQs.mp4 > <http://unleashkids.org/%7Eholt/10new/LDyMYyiAsQs.mp4> is 93.8% of > 8.4M LDyMYyiAsQs.mp4 > <http://unleashkids.org/%7Eholt/10old/LDyMYyiAsQs.mp4> > 6. bcCLKACsYJ0.mp4 > <http://unleashkids.org/%7Eholt/10new/bcCLKACsYJ0.mp4> is 49.5% of > 6.1M bcCLKACsYJ0.mp4 > <http://unleashkids.org/%7Eholt/10old/bcCLKACsYJ0.mp4> > 7. do8WhQaAyso.mp4 > <http://unleashkids.org/%7Eholt/10new/do8WhQaAyso.mp4> is is 33.5% of > 25M do8WhQaAyso.mp4 > <http://unleashkids.org/%7Eholt/10old/do8WhQaAyso.mp4> > 8. iPROoc_o0p8.mp4 > <http://unleashkids.org/%7Eholt/10new/iPROoc_o0p8.mp4> is 32.7% of 10M > iPROoc_o0p8.mp4 <http://unleashkids.org/%7Eholt/10old/iPROoc_o0p8.mp4> > 9. kkrF9X6Fycg.mp4 > <http://unleashkids.org/%7Eholt/10new/kkrF9X6Fycg.mp4> is 40.0% of > 3.5M kkrF9X6Fycg.mp4 > <http://unleashkids.org/%7Eholt/10old/kkrF9X6Fycg.mp4> > 10. meibWcbGqt4.mp4 > <http://unleashkids.org/%7Eholt/10new/meibWcbGqt4.mp4> is 55.2% of 13M > meibWcbGqt4.mp4 <http://unleashkids.org/%7Eholt/10old/meibWcbGqt4.mp4> > > AVG: compressed file is 41.0% of ORIGINAL, suggesting the 236GB of English > total may end up around 97GB, perfect (if the quality suffices!) > > Thanks All !! > > Challenge: if you do have a chance to express your feedback after viewing > several of the videos (new ones, on the LEFT) please also try your device > in landscape mode vs. portrait mode ...to see if that makes any difference > to the perceived quality/experience of the vid?! > > > PS long-term we're aware a further transcoding to WebM and/or OGV is also > necessary for compatibility on XO laptops and truly free OS's everywhere, > as such Emmanuel Engelhart (founder of Kiwix.org) may in fact be assisting > us+all here in coming months (: > > _______________________________________________ > Server-devel mailing list > Server-devel@lists.laptop.org > http://lists.laptop.org/listinfo/server-devel > >
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