[FFmpeg-devel] [PATCH] avformat/demux: Add allow_codec_changes option to AVFormatContext (v2)

[Pavel Koshevoy]

On Sat, Jun 21, 2025 at 3:38 PM Michael Niedermayer <michael at niedermayer.cc>
wrote:

> On Sat, Jun 21, 2025 at 03:26:58PM -0600, Pavel Koshevoy wrote:
> > On Sat, Jun 21, 2025 at 3:21 PM Michael Niedermayer <
> michael at niedermayer.cc>
> > wrote:
> >
> > > On Tue, Jun 17, 2025 at 08:36:59AM -0600, Pavel Koshevoy wrote:
> > > > Make runtime AVStream.codecpar codec_id updates optional and disabled
> > > > by default, so that avformat API clients can enable this feature
> > > explicitly
> > > > when they add support for runtime codec changes.
> > > >
> > > > Accordingly, codec_close should not assume that the codec_id cannot
> > > change.
> > > > This fixes 'ffprobe 1_poc.mp4' segfault introduced with
> > > > commit 0021484d05f9b0f032fa319399de6e24eea0c04f.
> > > > ---
> > > >  doc/APIchanges              |  3 +++
> > > >  doc/formats.texi            |  6 ++++++
> > > >  libavformat/avformat.h      | 10 ++++++++++
> > > >  libavformat/demux.c         |  8 +++++++-
> > > >  libavformat/mpegts.c        |  4 +++-
> > > >  libavformat/options_table.h |  1 +
> > > >  libavformat/version.h       |  2 +-
> > > >  tests/fate/demux.mak        |  2 +-
> > > >  8 files changed, 32 insertions(+), 4 deletions(-)
> > >
> > > [...]
> > >
> > > > diff --git a/libavformat/demux.c b/libavformat/demux.c
> > > > index ecd4f40da9..3749ab67a3 100644
> > > > --- a/libavformat/demux.c
> > > > +++ b/libavformat/demux.c
> > > > @@ -1292,9 +1292,15 @@ static int codec_close(FFStream *sti)
> > > >  {
> > > >      AVCodecContext *avctx_new = NULL;
> > > >      AVCodecParameters *par_tmp = NULL;
> > > > +    const AVCodec *new_codec = NULL;
> > > >      int ret;
> > > >
> > > > -    avctx_new = avcodec_alloc_context3(sti->avctx->codec);
> > > > +    new_codec =
> > > > +      (sti->avctx->codec_id != sti->pub.codecpar->codec_id) ?
> > > > +      avcodec_find_decoder(sti->pub.codecpar->codec_id) :
> > > > +      sti->avctx->codec;
> > > > +
> > > > +    avctx_new = avcodec_alloc_context3(new_codec);
> > > >      if (!avctx_new) {
> > > >          ret = AVERROR(ENOMEM);
> > > >          goto fail;
> > >
> > > this should be a seperate patch
> > >
> >
> > It already exists as a separate patch:
> > https://ffmpeg.org/pipermail/ffmpeg-devel/2025-June/344890.html
>
> it should not be in "avformat/demux: Add allow_codec_changes option to
> AVFormatContext"
>

Okay, submitted a separate patch just for allow_codec_changes here:
https://ffmpeg.org/pipermail/ffmpeg-devel/2025-June/345613.html
Note, that https://ffmpeg.org/pipermail/ffmpeg-devel/2025-June/344890.html
is still required to actually fix the `ffplay -allow_codec_changes 1 -i
1_poc.mp4` segfault.



>
> the allow_codec_changes patch is ok without this
>
> thx
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> No great genius has ever existed without some touch of madness. --
> Aristotle
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