[FFmpeg-user] 2 pass encoding with hevc_nvenc

[Reindl Harald]

Am 04.09.2016 um 14:45 schrieb Carl Eugen Hoyos:
> 2016-09-04 14:38 GMT+02:00 Reindl Harald <h.reindl at thelounge.net>:
>>
>> Am 04.09.2016 um 14:32 schrieb Carl Eugen Hoyos:
>>>
>>> 2016-09-04 14:00 GMT+02:00 Reindl Harald <h.reindl at thelounge.net>:
>>>>
>>>> Am 04.09.2016 um 13:57 schrieb Peter White:
>>>>>
>>>>> But the encoding time doubles--not worth it
>>>>
>>>> with smart params it don't double
>>>>
>>>> the first pass can be with a faster profile
>>>
>>>> and skip audio entirely
>>>
>>> This can have bad effects with FFmpeg and x264:
>>> If you are lucky, you get a crash, in the worst case,
>>> encoding succeeds but you get worse quality than
>>> one-pass (wrong frames get the low quantizers)
>>
>> given that we use it for a long time now as default in our
>> ffmpeg-wrapper, files are typically smaller than with
>> single-pass and the quality is as expected the point is "can"
>>
>> long time means over years for all sort of videos
>
> It depends on the output format and I suspect it also
> depends on sync implementation that can change
> without real notice.
>
> Allow me to repeat that the true problem is that you may
> not notice issues: Encoding succeeds but the quantizers
> are incorrectly dsitributed (starting from the second frame).
> You only get the crash if you are lucky

if i don't 'notice issues' which means for me i don't see bad quality 
and it plays on every device then there is no 'issue'

you get a 'crash' if you differ with completly incompatible params 
between the two passes

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