[FFmpeg-user] size and bitrate issues with nvidia accelerated transcoding

Sreenath BH bhsreenath at gmail.com
Tue Mar 8 17:54:16 CET 2016

On 3/8/16, Moritz Barsnick <barsnick at gmx.net> wrote:
> Hi Sreenath,
> On Mon, Mar 07, 2016 at 22:28:32 +0530, Sreenath BH wrote:
>> As can be seen the two outputs differ in the H264 profile(High vs
>> Main), bitrate, the pixel format and of course the file sizes.
> Different encoders can have different defaults. It appears that nvenc
> defaults to "Main", while libx264 defaults to preset "medium" which
> apparently implies "High" (but might depend on other things).
> If you want the same profiles and levels, you will need to request them
> explicitly.
> The same thing goes for the quality: libx264 defaults to crf=23, I
> don't know about nvenc. Furthermore, encoders can trade off quality (or
> size) for conversion speed. So if you want the same size, you have to
> specify "-b:v" explicitly. If you want the same quality, I guess you
> may have to experiment with the settings available to find something
> comparable.
> And finally, don't expect the same results as soon as you have the same
> profile, levels and bitrate (or quality). One encoder will be more
> efficient than the other, or give different results in different scene
> scenarios.
> Does this clarify some things?
> Moritz
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Thanks for your comments. I understand that two codecs even with same
presets and other similar settings can produce differing output.

I wanted to know if there was a way to achieve the results I wanted
with the codec we prefer to use (nvidia) because it have significant
speed increase.


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