[FFmpeg-devel] [PATCH 1/2] libavfilter/scale: More descriptive in/ref/out logging

Kevin Mark kmark937 at gmail.com
Mon Jun 12 07:59:23 EEST 2017

Hi Michael,

Hoping to get your thoughts on the grepability issue (wrt my previous
email). If it needs to be on a single line there's no reason the new format
cannot be changed to do so (removing the \n and adding a separator,
really). However I'm a big fan of it as-is (for both scale and scale2ref)
and I can't find a case of my own where the regex I proposed would be


On Tue, Jun 6, 2017 at 4:17 PM Kevin Mark <kmark937 at gmail.com> wrote:

> On Tue, Jun 6, 2017 at 11:49 AM, Michael Niedermayer
> <michael at niedermayer.cc> wrote:
> > yes but its much harder to grep for as its not a single line anymore
> I agree that it's not going to be as pretty a regular expression to
> grep through, as there is 33% more data, but it should still be doable
> without too much effort. How important is it that we maintain "API"
> compatibility on verbose CLI output?
> ffmpeg [...] scale2ref=0:0 [...] -v verbose - 2>&1 >/dev/null | grep -oP
> 'regex'
> Where regex is:
> (in|out|ref) +w:(\d+) h:(\d+) fmt:(\w+) sar:(\d+)\/(\d+)(?:
> flags:0x[[:xdigit:]]+)?
> Assuming GNU grep 2.25+, you'll get:
> in  w:320 h:240 fmt:rgb24 sar:1/1
> ref w:640 h:360 fmt:rgb24 sar:1/1
> out w:640 h:360 fmt:rgb24 sar:3/4 flags:0x2
> It also works with BSD grep 2.5.1-FreeBSD included in macOS if you use
> the -E option instead of -P. These would be considered three separate
> matches so if you're using a good regex engine it'd be pretty easy to
> loop over each match, check the first group to determine if it's in,
> ref, or out and act accordingly on the rest of the captured data. You
> could also, if you wanted, assume that the first line is in and the
> second line is out if you only have two matches (or lines even) and if
> you have three matches/lines the first is in, second is ref, third is
> out. If you needed it to work with less sophisticated engines it
> shouldn't be too hard to dumb down the regex above.
> Live-ish example: https://regex101.com/r/wvHLpa/1
> Is there a special property that makes single lines much easier to
> grep? Something specific to bash? I wouldn't think bash would have any
> problems looping over this by line.
> Thanks,
> Kevin

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