[FFmpeg-devel] [PATCH 2/2] avformat: add avformat_flush()

[Michael Niedermayer]

On Mon, Sep 29, 2014 at 08:34:44PM +0200, wm4 wrote:
> On Mon, 29 Sep 2014 20:25:47 +0200
> Michael Niedermayer <michaelni at gmx.at> wrote:
> 
> > On Mon, Sep 29, 2014 at 07:41:28PM +0200, wm4 wrote:
> > > Useful for Bluray and DVD, since the libraries used to read them just
> > > change the byte stream under your feet on seeking.
> > > 
> > > Maybe there should be a AVInputFormat callback for this. But the
> > > mpeg-ps (DVD) and the mpeg-ts (Bluray) demuxers don't change much
> > > state during seeking - they just try to find a new packet with
> > > timestamps (in read_timestamp), so I haven't found a need for this
> > > yet. I don't want to add unused things.
> > > 
> > > I've also thought about adding a flush callback, and implementing
> > > them in mpeg.c and mpegts.c by just calling ff_read_frame_flush().
> > > Might be slightly better, because you can have avformat_flush() fail
> > > on formats which don't support this?
> > > 
> > > Or maybe a flag?
> > > 
> > > TODO: add entry to APIchanges, bump minor version.
> > > ---
> > >  libavformat/avformat.h | 13 +++++++++++++
> > >  libavformat/utils.c    |  6 ++++++
> > >  2 files changed, 19 insertions(+)
> > > 
> > > diff --git a/libavformat/avformat.h b/libavformat/avformat.h
> > > index 78054de..eaa52fa 100644
> > > --- a/libavformat/avformat.h
> > > +++ b/libavformat/avformat.h
> > > @@ -2173,6 +2173,19 @@ int av_seek_frame(AVFormatContext *s, int stream_index, int64_t timestamp,
> > >  int avformat_seek_file(AVFormatContext *s, int stream_index, int64_t min_ts, int64_t ts, int64_t max_ts, int flags);
> > >  
> > >  /**
> > > + * Discard all internally buffered data. This can be useful when dealing with
> > > + * discontinuities in the byte stream. Generally works only with some simple
> > > + * formats.
> > 
> > id call them stream based or without a central header instead of
> > simple.
> 
> I can change that and replace "simple" with "headerless".

please do, headerless is more specific


> 
> > 
> > > + *
> > > + * This does not flush the AVIOContext (s->pb). If necessary, call
> > > + * avio_flush(s->pb) before calling this function.
> > > + *
> > > + * @param s media file handle
> > > + * @return >=0 on success, error code otherwise
> > > + */
> > > +int avformat_flush(AVFormatContext *s);
> > 
> > i think this should document what happens with the streams
> > are they flushed too so that nb_streams could decrease ...
> > i guess the case where they could decrease doesnt make much sense
> > as that can already be achived by closing the demuxer and reopening
> > it ...
> 
> Removing the AVStreams would be not useful; keeping the streams around
> is in fact this is the reason why reopening might not work, and
> avformat_flush() is needed at all.
> 

> I can add something to the doxygen to explain this. Maybe: "The set of
> streams, the detected duration, stream parameters and codecs do not
> change when calling this function."

sounds good

thx

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

The misfortune of the wise is better than the prosperity of the fool.
-- Epicurus
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