[FFmpeg-user] How to decode one frame and encode one jpg if using qscale

[penguin flying]

but if we DID NOT add qscale,  we can get one picture after sending one
frame the the encoder at the same time; even if the src file having B frames



Carl Eugen Hoyos <ceffmpeg at gmail.com> 于2020年3月17日周二 下午11:13写道：

> Am Di., 17. März 2020 um 16:04 Uhr schrieb penguin flying
> <theflyingpenguin2020 at gmail.com>:
> >
> > using this cmd
> > ffmpeg -i in.mp4  -copyts -f image2 -vframes 5   -y %03d.jpg
> > will decode one frame and then encode it to one jpg at the same time,
> > AND the picture will be encoded in default quality.
> >
> > BUT when I want to improve the quality of the image after adding the
> param
> > "qscale",
> > ffmpeg -i in.mp4  -copyts -f image2 -vframes 5 -qscale:v 2   -y %03d.jpg
> >
> > I found that three or more frames must be send to the encoder before the
> > first jpg comes out.
> >
> > How to send one frame and then one picture out when using "qscale"
>
> The output option -threads 1 should ensure this...
>
> > PS: the source file  in.mp4 has B frames
>
> ... but this may not be possible for streams with B frames.
>
> Carl Eugen
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