[FFmpeg-devel] [PATCH] lavfi/buffersrc: issue more specific error in case of invalid parameters

[Anton Khirnov]

Quoting Stefano Sabatini (2023-03-01 01:05:29)
> On date Wednesday 2023-03-01 01:01:26 +0100, Stefano Sabatini wrote:
> > ---
> >  libavfilter/buffersrc.c | 13 ++++++++++---
> >  1 file changed, 10 insertions(+), 3 deletions(-)
> > 
> > diff --git a/libavfilter/buffersrc.c b/libavfilter/buffersrc.c
> > index ba17450b93..ea9556d691 100644
> > --- a/libavfilter/buffersrc.c
> > +++ b/libavfilter/buffersrc.c
> > @@ -273,9 +273,16 @@ static av_cold int init_video(AVFilterContext *ctx)
> >  {
> >      BufferSourceContext *c = ctx->priv;
> >  
> > -    if (c->pix_fmt == AV_PIX_FMT_NONE || !c->w || !c->h ||
> > -        av_q2d(c->time_base) <= 0) {
> > -        av_log(ctx, AV_LOG_ERROR, "Invalid parameters provided.\n");
> > +    if (c->pix_fmt == AV_PIX_FMT_NONE) {
> > +        av_log(ctx, AV_LOG_ERROR, "Unspecified pixel format\n");
> > +        return AVERROR(EINVAL);
> > +    }
> > +    if (!c->w || !c->h) {
> > +        av_log(ctx, AV_LOG_ERROR, "Invalid null size %dx%d\n", c->w, c->h);
> > +        return AVERROR(EINVAL);
> > +    }
> > +    if (av_q2d(c->time_base) <= 0) {
> > +        av_log(ctx, AV_LOG_ERROR, "Invalid time base %d/%d\n", c->time_base.num, c->time_base.den);
> >          return AVERROR(EINVAL);
> >      }
> 
> BTW, I noticied this as part of debugging transcode.c (which looks
> broken at the moment), since the timebase is read as 0/1 from the
> decoder context, it would be a valid value when reading from the
> AVStream (but this information is not copied by
> avcodec_parameters_to_context). In decode_filter_video.c this is
> indeed "fixed" by copying the timebase directly from the AVStream.
> 
> Is this expected? Shouldn't the timebase be copied to the decoder
> context?

Historically, AVCodecContext.time_base for decoding was NOT (as one
might expect) the timebase of input packets, set by the user. It was
instead the inverse of the framerate stored in codec-level headers,
which was called "codec timebase" by some documents.

Since that was massively confusing for pretty much everyone, I added
AVCodecContext.framerate for exporting the framerate from the decoder,
and deprecated the use of AVCodecContext.time_base for decoding
entirely. After the recent major bump, time_base should not be used at
all in any way when decoding.

The timebase of input packets should instead be stored in
AVCodecContext.pkt_timebase. I suppose after some time has passed we
might want to merge its functionality into time_base.

-- 
Anton Khirnov