[FFmpeg-devel] [PATCH] avformat/avformat.h: Add av_stream_remove_side_data.

[Michael Niedermayer]

On Tue, Jul 03, 2018 at 12:14:19PM -0700, Jacob Trimble wrote:
> On Mon, Jul 2, 2018 at 6:07 PM Michael Niedermayer
> <michael at niedermayer.cc> wrote:
> >
> > On Mon, Jun 25, 2018 at 04:03:32PM -0700, Jacob Trimble wrote:
> > > Signed-off-by: Jacob Trimble <modmaker at google.com>
> > > ---
> > >  libavformat/avformat.h |  8 ++++++++
> > >  libavformat/utils.c    | 11 +++++++++++
> > >  2 files changed, 19 insertions(+)
> >
> >
> >
> >
> >
> > >
> > > diff --git a/libavformat/avformat.h b/libavformat/avformat.h
> > > index fdaffa5bf4..434c88837e 100644
> > > --- a/libavformat/avformat.h
> > > +++ b/libavformat/avformat.h
> > > @@ -2167,6 +2167,14 @@ AVStream *avformat_new_stream(AVFormatContext *s, const AVCodec *c);
> > >  int av_stream_add_side_data(AVStream *st, enum AVPacketSideDataType type,
> > >                              uint8_t *data, size_t size);
> > >
> > > +/**
> > > + * Removes any existing side data of the given type.
> > > + *
> > > + * @param st stream
> > > + * @param type side information type
> > > + */
> > > +void av_stream_remove_side_data(AVStream *st, enum AVPacketSideDataType type);
> >
> > What would use this and why ?
> > The commit message does not explain this
> >
> > If side data is changing it probably should be put in AVPackets or AVFrames
> > not the stream.
> >
> 
> I am using this to removing the side data that contains the
> AVEncryptionInitInfo objects once I handle them.  Since an MP4 file
> can contain multiple pssh atoms, there can be multiple
> AVEncryptionInitInfo structs.  To make it easier for me, I want to
> remove the side data that contain them once I have handled them.  This
> means that if the AVStream contains the side data, it is because of
> new init info I haven't seen.  Since the pssh atoms are more "global"
> it makes more sense to put them in the AVStream.

I dont fully understand but
If you intend to remove things while reading the "header" of a mp4 file
these things probably should not be in side data to begin with but be
internal to the demuxer.

otherwise, after the header or outside the demuxer removal seems a "no go"
but i may misunderstand what you intend to do. Please explain if iam 
totally off here with how i interpret this

One simple API good vs. bad test btw should be to consider that theres
a demuxer connected to a muxer.
If this does not work to produce a equivalent file the API is not good
for example if you change side data in the AVStream in the middle between
outputing packets i would not expect the muxer to see this and thus not
be able to reproduce this in the stored file.

Also if you mess with the demxuers side data from outside, not only
will this result in undefined behavior it also might be that you still
need it when for example seeking back to the start

again maybe i totally misunderstand what you intend here


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The worst form of inequality is to try to make unequal things equal.
-- Aristotle
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