[FFmpeg-user] 2 pass encoding with hevc_nvenc

Reindl Harald h.reindl at thelounge.net
Sun Sep 4 15:48:09 EEST 2016

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

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 181 bytes
Desc: OpenPGP digital signature
URL: <http://ffmpeg.org/pipermail/ffmpeg-user/attachments/20160904/7d4a276e/attachment.sig>

More information about the ffmpeg-user mailing list