Why enconding using NVENC the file size is bigger than x264 ?

[Aug]

Thanks for reading my topic.
Here is Linux Lubuntu 24.04.3 kernel 6.14 using a GT 640 driver 470.
I see when enconding using nvenc the file is much more big than if using x264 cpu enconding.
Why happen it ?
I have tested using and disabling b frames and is the same result.
Have a nice week.

[jagabo]

Different encoders + different settings = different file size

[pandy]

NVENC encoder usually need more bitrate to deliver same/comparable quality - software encoders usually offers higher compression at a cost of encoding time - hardware encoders such as NVENC usually need to use simpler encoding techniques but in exchange they offer encoding speed way higher than software encoders - there is always trade-off between bitrate/quality/encoding speed

[jagabo]

hardware encoders such as NVENC usually need to use simpler encoding techniques but in exchange they offer encoding speed way higher than software encoders

Maybe not on a GT 640. x264 at the veryfast preset may be faster and deliver better quality per bitrate.

[pandy]

hardware encoders such as NVENC usually need to use simpler encoding techniques but in exchange they offer encoding speed way higher than software encoders

Maybe not on a GT 640. x264 at the veryfast preset may be faster and deliver better quality per bitrate.

Depends on CPU and quite important - x264 at veryfast preset probably will require higher bitrate to deliver same or comparable quality to one offered by NVENC is highest quality settings - so still NVENC may be better in situation when you can accept bitrate higher for example by 20% but your goal is encoding speed.

It could be interesting exercise to check where is intersection point (x264 vs NVENC) - sadly i can't perform such exerciser as i have no NVidia card equipped with NVENC (and AMD video encoders are way worse than NVidia) - perhaps Intel encoders can match NVidia.

[Selur]

I do not think the he is really using nvenc => https://forum.videohelp.com/threads/420970-Why-b-frames-not-does-less-file-size#post2801937

[pandy]

I do not think the he is really using nvenc => https://forum.videohelp.com/threads/420970-Why-b-frames-not-does-less-file-size#post2801937

No clue - OP asked about NVENC - HW encoding focus on speed not on quality - of course broadcast encoders may deliver HQ in real time but still software encoders working without time constrains usually are able to deliver highest quality and at the same lowest bitrate.

[Selur]

... using a GT 640 ...

[pandy]

... using a GT 640 ...

True but...

I see when enconding using nvenc

And rule is quite universal - HW faster but more bitrate for same quality or software - slower but lower bitrate for same quality