[FFmpeg-user] 2 pass encoding with hevc_nvenc

Carl Eugen Hoyos ceffmpeg at gmail.com
Sun Sep 4 15:45:10 EEST 2016

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.

Carl Eugen

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