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

[Pavel Koshevoy]

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