[FFmpeg-devel] [PATCH] avcodec/av1dec: Adjust incorrect error output

[Soft Works]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of
> Wang, Fei W
> Sent: Tuesday, 24 August 2021 07:32
> To: ffmpeg-devel at ffmpeg.org
> Subject: Re: [FFmpeg-devel] [PATCH] avcodec/av1dec: Adjust incorrect
> error output
> 
> On Tue, 2021-08-24 at 02:45 +0000, Soft Works wrote:
> > > -----Original Message-----
> > > From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of
> > > Ronald S. Bultje
> > > Sent: Tuesday, 24 August 2021 04:34
> > > To: FFmpeg development discussions and patches <ffmpeg-
> > > devel at ffmpeg.org>
> > > Subject: Re: [FFmpeg-devel] [PATCH] avcodec/av1dec: Adjust
> > > incorrect
> > > error output
> > >
> > > Hi,
> > >
> > > On Mon, Aug 23, 2021 at 9:39 PM Soft Works
> <softworkz at hotmail.com>
> > > wrote:
> > >
> > > > The current message "Your platform doesn't suppport
> > > > hardware accelerated AV1 decoding." is inaccurate and
> > > > misleading. When a user doesn't specify a hwcaccel,
> > > > this doesn't tell anything about what is actually
> > > > supported on that platform.
> > > >
> > > > Signed-off-by: softworkz <softworkz at hotmail.com>
> > > > ---
> > > >  libavcodec/av1dec.c | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/libavcodec/av1dec.c b/libavcodec/av1dec.c
> > > > index a75d6744d3..8dfcd26cb6 100644
> > > > --- a/libavcodec/av1dec.c
> > > > +++ b/libavcodec/av1dec.c
> > > > @@ -462,8 +462,8 @@ static int get_pixel_format(AVCodecContext
> > >
> > > *avctx)
> > > >       * implemented in the future, need remove this check.
> > > >       */
> > > >      if (!avctx->hwaccel) {
> > > > -        av_log(avctx, AV_LOG_ERROR, "Your platform doesn't
> > >
> > > suppport"
> > > > -               " hardware accelerated AV1 decoding.\n");
> > > > +        av_log(avctx, AV_LOG_ERROR, "AV1 decoding requires a
> hw
> > > > acceleration"
> > > > +               " to be specified.\n");
> > > >
> > >
> > > This is misleading.
> > >
> > > This error message (for me) happens when I accidentally compile
> > > FFmpeg
> > > without aom/dav1d support, and try to play AV1 content.
> >
> > It also happens to me when I specify:
> >
> > ffmpeg -c:v av1 -i INPUT OUTPUT
> >
> > (e.g. like when I'd have forgotten to specify the hwaccel)
> >
> > > AV1 decoding
> > > does
> > > not require hw decoding - it simply requires an external library.
> > >
> > > Will the hwaccel be autodetected when AV1 hw decoding is
> supported
> > > by
> > > the
> > > platform?
> >
> > No.
> >
> > How about this: "The AV1 decoder requires a hw acceleration to be
> > specified." ?
> 
> This will bring new misleading if user specify the hw acceleration
> but
> the hardware itself doesn't support av1 dec.

Such situations may happen, but this is not subject of this patch.
This patch is about the error that is printed when no hw acceleration
has been specified.

If the specified hw accel is not available or cannot be initialized,
then there will be an error reported at an earlier stage.

If the specified hw accel has been initialized successfully but the
hwaccel doesn't support AV1, this check won't catch it anyway.

Kind regards,
softworkz