[FFmpeg-user] Why ffmpeg libx265 generate way smaller files than cuda/nvidia based one?

[Mick Finn]

> On Aug 6, 2022, at 2:02 AM, jatmvp ctf <justanotherteammate at gmail.com> wrote:
> 
> Maybe my question is not correct. If both encode H.265 but I thought the
> performance ability (to create compression ratio) should be the same or at
> least comparable.
> 
> That means CUDA version is only for some purposes and traditional open
> libx265 version for others? I guess, the CUDA is only for streaming, but
> then the decrease size of frames ( so increased compression ratio) to
> produce fast
> 
> Harald, could you elaborate about those because I am really excited to know
> about it. Maybe I have compiled something wrong. I've been looking at it
> from yesterday so maybe I missed something in documentation :)
> 
> Best regards.
> 
> pt., 5 sie 2022 o 18:38 jatmvp ctf <justanotherteammate at gmail.com>
> napisał(a):
> 
>> Different implementation of same standard should not behave way different
>> I assume, or not have same features or performance (at least).
>> 
>> Could you describe a little more or at least give source?
>> 
>> What are you suggesting by different implementation exactly then?
>> 
>> I guess from your short message that CPU is OK and nVidia's is bad, saying
>> - "it is different" but for me it is not metrics when you not give facts
>> 
>> pt., 5 sie 2022 o 17:46 Reindl Harald <h.reindl at thelounge.net> napisał(a):
>> 
>>> 
>>> 
>>>> Am 05.08.22 um 17:02 schrieb jatmvp ctf:
>>>>> I have problem with understanding why my ffmpeg with nVidia features (as
>>>>> v:c hevc_nvenc) generate way larger file in comparison to libx265
>>> 
>>> because it's a different implementation
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>> 
There are a lot of control parameters that are probably set different for the two implementations. The GPU implementation has obvious advantages on floating point calculations that might improve the compression ratio.
Some hints at the parameters that would be in play:

https://uca.edu/cse/files/2020/07/A_Study_of_Rate_Control_for_H.265_HEVC_Video_Compression.pdf

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