[FFmpeg-devel] 回复： [PATCH] avcodec/videotoolboxenc: add low-latency encoding

[Zhao Zhili]

> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of Rick Kern
> Sent: 2023年5月20日 23:01
> To: FFmpeg development discussions and patches <ffmpeg-devel at ffmpeg.org>
> Subject: Re: [FFmpeg-devel] 回复： [PATCH] avcodec/videotoolboxenc: add low-latency encoding
> 
> On Fri, May 19, 2023 at 2:06 PM Zhao Zhili <quinkblack at foxmail.com> wrote:
> 
> >
> > > From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of Rick
> > Kern
> > > Sent: 2023年5月19日 21:37
> > > To: FFmpeg development discussions and patches <ffmpeg-devel at ffmpeg.org>
> > > Cc: zhilizhao(赵志立) <quinkblack at foxmail.com>
> > > Subject: Re: [FFmpeg-devel] 回复： [PATCH] avcodec/videotoolboxenc: add
> > low-latency encoding
> > >
> > > On Fri, May 19, 2023 at 1:56 AM 徐福隆 <839789740 at qq.com> wrote:
> > >
> > > > Thank you for your review, and point out the details.
> > > > Actually, I have also considered this issue.
> > > > I see that some keys are used directly, some are used by compatibility.
> > > >
> > >
> > > The compat_keys are used for symbols that might not exist. For constants
> > > available in the earliest version of VideoToolbox, compat_keys doesn't
> > need
> > > to be used.
> >
> > I curious to know what's the minimum supported version of macOS which
> > doesn't need dynamic loading symbols. I can't find such information. The
> > question
> > applies to other OS too. It's not clear from configure, and I can't find
> > the relevant
> > documentation.
> >
> VideoToolbox was released in MacOS 10.8 and iOS 8.0. I'll update the
> compat_keys docs with this info.

Maybe it's off-topic, but besides than the first version of MacOS which has
videotoolbox supports, I'm considering the strategy from FFmpeg's side: how
to decide when to bump the minimum supported version of OS, like
"[RFC] [Vote] Drop Windows XP support".

https://ffmpeg.org/pipermail/ffmpeg-devel/2017-December/222354.html

I'm not saying it's time to bump the required version of macOS now, but as
time goes by, we might need to do that in the future for other OS, to relief the
maintaining burden.

> 
> 
> > >
> > > Your patch looks good - I'll push it shortly.
> > >
> > >
> > > > I will use compat_key instead, and submit a new patch.
> > > >
> > > >
> > > > ------------------ 原始邮件 ------------------
> > > > 发件人:
> > > >                                                   ""zhilizhao(赵志立)""
> > > >
> > > > <quinkblack at foxmail.com>;
> > > > 发送时间: 2023年5月19日(星期五) 中午11:34
> > > > 收件人: "FFmpeg development discussions and patches"<
> > > > ffmpeg-devel at ffmpeg.org>;
> > > > 抄送: "徐福隆"<839789740 at qq.com>;
> > > > 主题: Re: [FFmpeg-devel] [PATCH] avcodec/videotoolboxenc: add
> > > > low-latency encoding
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > > On May 19, 2023, at 11:17, xufuji456 <839789740 at qq.com> wrote:
> > > > >
> > > > > When using low-latency mode, it eliminates frame reordering
> > > > > and follows a one-in-one-out encoding mode
> > > > >
> > > > > Signed-off-by: xufuji456 <839789740 at qq.com>
> > > > > ---
> > > > > libavcodec/videotoolboxenc.c | 11 +++++++++++
> > > > > 1 file changed, 11 insertions(+)
> > > > >
> > > > > diff --git a/libavcodec/videotoolboxenc.c
> > > > b/libavcodec/videotoolboxenc.c
> > > > > index c6f22723d6..ae1ef32b2d 100644
> > > > > --- a/libavcodec/videotoolboxenc.c
> > > > > +++ b/libavcodec/videotoolboxenc.c
> > > > > @@ -1441,6 +1441,17 @@ static int
> > > > vtenc_create_encoder(AVCodecContext   *avctx,
> > > > >         }
> > > > >     }
> > > > >
> > > > > +    // low-latency mode: eliminate frame
> > reordering,
> > > > follow a one-in-one-out encoding mode
> > > > > +    if ((avctx->flags &
> > > > AV_CODEC_FLAG_LOW_DELAY) && avctx->codec_id ==
> > AV_CODEC_ID_H264)
> > > > {
> > > > > +        status =
> > > > VTSessionSetProperty(vtctx->session,
> > > > >
> > > >
> > >
> >
> +                  &nbsp
> > >
> > ;                  
> > > > kVTVideoEncoderSpecification_EnableLowLatencyRateControl,
> > > > >
> > > >
> > >
> >
> +                  &nbsp
> > >
> > ;                  
> > > > kCFBooleanTrue);
> > > >
> > > > Please use compat_keys in case of
> > > > kVTVideoEncoderSpecification_EnableLowLatencyRateControl
> > > > isn’t available.
> > > >
> > > > > +
> > > > > +        if (status) {
> > > > >
> > +           
> > > > av_log(avctx, AV_LOG_ERROR, "Error setting low latency property: %d\n",
> > > > status);
> > > > > +        }
> > > > > +    }
> > > > > +
> > > > >     status =
> > > > VTCompressionSessionPrepareToEncodeFrames(vtctx->session);
> > > > >     if (status) {
> > > > >         av_log(avctx,
> > > > AV_LOG_ERROR, "Error: cannot prepare encoder: %d\n", status);
> > > > > --
> > > > > 2.32.0 (Apple Git-132)
> > > > >
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