[FFmpeg-devel] [PATCH] avformat: close parser if codec changed

[Michael Niedermayer]

On Wed, Nov 02, 2016 at 10:30:30PM +0100, Andreas Cadhalpun wrote:
> On 02.11.2016 13:07, Michael Niedermayer wrote:
> > On Sat, Oct 22, 2016 at 01:16:00AM +0200, Andreas Cadhalpun wrote:
> >>  utils.c |   12 ++++++++++++
> >>  1 file changed, 12 insertions(+)
> >> ffefc22756b774cb7652587207ae66cfbf681be3  0001-avformat-close-parser-if-codec-changed.patch
> >> From 9de87a4fb2c6c6311a11a2da5de8554a71adfa66 Mon Sep 17 00:00:00 2001
> >> From: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
> >> Date: Mon, 17 Oct 2016 20:26:51 +0200
> >> Subject: [PATCH] avformat: close parser if codec changed
> >>
> >> The parser depends on the codec and thus must not be used with a different one.
> >> If it is, the 'avctx->codec_id == s->parser->codec_ids[0] ...' assert in
> >> av_parser_parse2 gets triggered.
> >>
> >> Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
> >> ---
> >>  libavformat/utils.c | 12 ++++++++++++
> >>  1 file changed, 12 insertions(+)
> >>
> >> diff --git a/libavformat/utils.c b/libavformat/utils.c
> >> index 70dbfa1..a8a78ed 100644
> >> --- a/libavformat/utils.c
> >> +++ b/libavformat/utils.c
> >> @@ -480,6 +480,12 @@ static int update_stream_avctx(AVFormatContext *s)
> >>          if (!st->internal->need_context_update)
> >>              continue;
> >>  
> >> +        /* close parser, because it depends on the codec */
> >> +        if (st->parser && st->internal->avctx->codec_id != st->codecpar->codec_id) {
> >> +            av_parser_close(st->parser);
> >> +            st->parser = NULL;
> >> +        }
> >> +
> >>          /* update internal codec context, for the parser */
> >>          ret = avcodec_parameters_to_context(st->internal->avctx, st->codecpar);
> >>          if (ret < 0)
> >> @@ -1515,6 +1521,12 @@ static int read_frame_internal(AVFormatContext *s, AVPacket *pkt)
> >>                  st->info->found_decoder = 0;
> >>              }
> >>  
> >> +            /* close parser, because it depends on the codec */
> >> +            if (st->parser && st->internal->avctx->codec_id != st->codecpar->codec_id) {
> >> +                av_parser_close(st->parser);
> >> +                st->parser = NULL;
> >> +            }
> >> +
> > 
> > what if the codec id differs but both are supported by the parser ?
> > AVCodecParser has a list of 5 codec ids ?
> > 
> > I didnt find a testcase where this makes a difference, just wondering
> 
> I think the parser should be re-initialized in that case, too.

doesnt this lead to data loss (parser internal buffers being lost at
a transition between 2 types)?
both types might be handled by the same decoder so nothing special
might be needed "downstream"


[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

There will always be a question for which you do not know the correct answer.
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