[FFmpeg-user] 4K Way to large to stream

Nicolas George george at nsup.org
Thu Jul 1 16:12:00 EEST 2021

Carl Zwanzig (12021-06-29):
> Like the "Good/Fast/Cheap - Pick two" metaphor, you have hit the
> quality/file-size/bandwidth trade-off. To keep the resolution at 4k and at
> good-to-excellent quality, perforce the files and bit-rate will be large- if
> you want the file to be smaller, even with very fancy encoding something
> must be discarded, could be resolution, could be frame rate, could be "quality".

Frame rate and resolution are both elements of quality.

In principle, codecs are capable of skipping frames or flattening
neighboring pixels, so they should be able to decide to reduce the frame
rate or resolution if it is the best choice. But in practice, codecs are
not that smart, and reducing the resolution will sometimes help.

> There's also the point that in many cases, super high quality is effectively
> wasted, for instance, 4k is only effective if the viewer has a 4k display;

... and excellent eyesight: for a normal/close viewing distance, the
separation power of the central area of our eye is about the size of a
pixel in a 2K video. Everything beyond that is only useful if we pause
and look closely.

> 5.1 sound is only effective if the listener has 5.1 playback equipment -and-
> the sound was mixed for that. etc.

This is true.

But you also missed something:

It is true that, unless we're using "-c:v kenjanoishi", in order to gain
something, for example file size, we have to sacrifice something of
equal value, and it is frequently quality. But there are other
possibilities than quality.

Compatibility is a possibility: the old file was playable by a DVD+DivX
player from the 2010s, the new file is not, but it is smaller. Using a
better codec or a more complex codec profile is a case of this.

Processing power is a possibility: the old file took 2 hours to encode,
the new file takes 10, but it will be smaller.

Nimbleness is a possibility: the old file allowed to seek at any half
second, the new file only allows to seek to scene changes, but it is

This is something to remember. Video encoding is a complex task.

Your advice was sound: for archival, better keep the original. Do not
recompress to gain a measly 25%. But for viewing, adapt the quality
compromise to the viewing conditions.


  Nicolas George
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