[FFmpeg-devel] Query regarding codec parsers

[Gautam Ramakrishnan]

On Fri, Apr 17, 2020 at 3:28 AM Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:
>
> Am Do., 16. Apr. 2020 um 12:24 Uhr schrieb Gautam Ramakrishnan
> <gautamramk at gmail.com>:
> >
> > On Mon, Apr 13, 2020 at 11:00 PM Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:
> > >
> > > Am Mo., 13. Apr. 2020 um 17:27 Uhr schrieb Gautam Ramakrishnan
> > > <gautamramk at gmail.com>:
> > > >
> > > > On Sun, Mar 29, 2020 at 8:34 PM Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:
> > > > >
> > > > > Am So., 29. März 2020 um 16:45 Uhr schrieb Gautam Ramakrishnan
> > > > > <gautamramk at gmail.com>:
> > > > >
> > > > > > > > What exactly does a parser do and how is it different from a decoder?
> > > > > > > > I am unable to understand the exact use case of a parser.
> > > > > > >
> > > > > > > Try the following:
> > > > > > > $ cat 1.jpg 2.jpg | ffmpeg -i -f null -
> > > > > > > (Is expected to decode two frames as can be seen in the console output,
> > > > > > > also works for example with png)
> > > > > > >
> > > > > > > $ cat 1.j2k 2.j2k | ffmpeg -i - -f null -
> > > > > > > Will only decode one frame because there is no parser to split the
> > > > > > > input.
> > > > > > >
> > > > > > So does it basically try to find the SOC marker and EOC markers and
> > > > > > split the streams into frames?
> > > > >
> > > > > Basically, yes.
> > > > > Look at existing parsers in libavcodec/*parser* (or git grep AVCodecParser),
> > > > > especially the jpeg parser.
> > >
> > > > Would working on a parser be a good idea now?
> > >
> > > Either that or you look at ticket #4681 (no idea how difficult this is).
>
> > I thought I'll start with the parser first.
> > I went through the BMP and JPEG parsers and needed some more clarification.
> > So, each frame could either be a JPEG2000 file or a JPEG2000 codestream.
> > The parse function must be able to find the end of the file/codestream
> > and return the location of it. Is my understanding correct?
>
> It is supposed to find the end of the first and the beginning of the
> second frame in above example, see what the jpg parser does.
>
> Carl Eugen
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Hi,

My issue was I guess particular to JPEG2000. Should we consider each
file as a frame,
or could even a codestream constitute a frame?


-- 
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Gautam |