[FFmpeg-devel] [PATCH] lavf: add ffprobe demuxer

[Stefano Sabatini]

On date Tuesday 2016-10-18 16:06:47 +0200, Michael Niedermayer encoded:
> On Tue, Oct 18, 2016 at 01:33:27PM +0200, Stefano Sabatini wrote:
> > On date Thursday 2016-10-13 19:46:41 +0200, Stefano Sabatini encoded:
> > > On date Thursday 2016-09-29 21:55:11 +0200, wm4 encoded:
> > [...]
> > > > This seems like a rather special use case. Why does it have a demuxer,
> > > > and can't be in your own C code using libavcodec/libavformat?
> > > > 
> > > 
> > > > In addition, I think using the ffprobe "format" is an overcomplication,
> > > > and will justify adding even more stuff to the demuxer, until it's a
> > > > similarily complex mess like the ffm demuxer/muxer.
> > > 
> > > I'm aware of the issue. OTOH I think the feature per-se is useful, at
> > > least for the two mentioned use cases (debugging - especially if
> > > coupled with a corresponding muxer), and data streams (generated by
> > > script) injection, since it relies on a textual format easily
> > > scriptable and editable by hand.
> > > 
> > > I thus leave the choice to the community. I guess this will require a
> > > vote if we cannot find an agreement.
> > > 
> > > Latest patch in attachment with ffprobe demuxer disabled by default,
> > > and extended documentation. (I'm also attaching the ff_get_line2 patch
> > > which is used by this new patch).
> > 
> > Updated, depends on the ff_get_line2() patch.
> > -- 
> > FFmpeg = Fanciful and Fundamentalist Magnificient Ponderous Elastic Game
> 
> >  configure                |    3 
> >  doc/demuxers.texi        |   18 ++
> >  doc/ffprobe-format.texi  |  121 ++++++++++++++
> >  doc/formats.texi         |    1 
> >  libavformat/Makefile     |    1 
> >  libavformat/allformats.c |    1 
> >  libavformat/ffprobedec.c |  405 +++++++++++++++++++++++++++++++++++++++++++++++
> >  7 files changed, 550 insertions(+)
> > 1d8a987564e907802dfd84722e3f5aafa69919ee  0002-lavf-add-ffprobe-demuxer.patch
> > From bef4930a2bf280425b5952de0e2281f03897ff7c Mon Sep 17 00:00:00 2001
> > From: Nicolas George <george at nsup.org>
> > Date: Sat, 11 Jan 2014 19:42:41 +0100
> > Subject: [PATCH] lavf: add ffprobe demuxer
> > 
> > With several modifications and documentation by Stefano Sabatini
> > <stefasab at gmail.com>.
> > 
> > Signed-off-by: Nicolas George <george at nsup.org>
> > ---
> [...]
> > +static int read_section_packet(AVFormatContext *avf, AVPacket *pkt)
> > +{
> > +    FFprobeContext *ffp = avf->priv_data;
> > +    uint8_t buf[4096];
> > +    int ret;
> > +    AVPacket p;
> > +    char flags;
> > +
> > +    av_init_packet(&p);
> > +    p.pos = avio_tell(avf->pb);
> > +    p.stream_index = -1;
> > +    p.size = -1;
> > +    av_bprint_clear(&ffp->data);
> > +    while ((ret = read_section_line(avf, buf, sizeof(buf)))) {
> > +        int has_time = 0;
> > +        int64_t pts, dts, duration;
> > +        char timebuf[1024];
> > +
> > +        if (ret < 0)
> > +            return ret;
> > +        if (sscanf(buf, "stream_index=%d", &p.stream_index)) {
> > +            if ((unsigned)p.stream_index >= avf->nb_streams) {
> > +                av_log(avf, AV_LOG_ERROR, "Invalid stream number %d specified in packet number %d\n",
> > +                       p.stream_index, ffp->packet_nb);
> > +                return AVERROR_INVALIDDATA;
> > +            }
> > +        }
> > +
> > +#define PARSE_TIME(name_, is_duration)                                  \
> > +        sscanf(buf, #name_ "=%"SCNi64, &p.name_);                       \
> 
> > +        has_time = sscanf(buf, #name_ "_time=%s", timebuf);             \
> 

> %s may be unsafe, not sure if theres a check elsewhere that prevents
> writing over the outut buffer

Now the buffer is big enough, since it has the same size of the read
line.
-- 
FFmpeg = Fanciful and Formidable Maxi Patchable Ecletic Geisha
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