Re: [FFmpeg-devel] [PATCH 1/2] avcodec: add null encoders

[Paul B Mahol <onemda@gmail.com>]

On Mon, Mar 14, 2022 at 1:12 PM James Almer <jamrial@gmail.com> wrote:

>
>
> On 3/14/2022 8:56 AM, Paul B Mahol wrote:
> > Signed-off-by: Paul B Mahol <onemda@gmail.com>
> > ---
> >   libavcodec/Makefile     |  2 ++
> >   libavcodec/allcodecs.c  |  2 ++
> >   libavcodec/codec_desc.c | 14 ++++++++++
> >   libavcodec/codec_id.h   |  2 ++
> >   libavcodec/nullenc.c    | 61 +++++++++++++++++++++++++++++++++++++++++
> >   5 files changed, 81 insertions(+)
> >   create mode 100644 libavcodec/nullenc.c
> >
> > diff --git a/libavcodec/Makefile b/libavcodec/Makefile
> > index cd929da8e6..8554b5ee7d 100644
> > --- a/libavcodec/Makefile
> > +++ b/libavcodec/Makefile
> > @@ -542,6 +542,8 @@ OBJS-$(CONFIG_MXPEG_DECODER)           += mxpegdec.o
> >   OBJS-$(CONFIG_NELLYMOSER_DECODER)      += nellymoserdec.o nellymoser.o
> >   OBJS-$(CONFIG_NELLYMOSER_ENCODER)      += nellymoserenc.o nellymoser.o
> >   OBJS-$(CONFIG_NOTCHLC_DECODER)         += notchlc.o
> > +OBJS-$(CONFIG_NULL_AUDIO_ENCODER)      += nullenc.o
> > +OBJS-$(CONFIG_NULL_VIDEO_ENCODER)      += nullenc.o
> >   OBJS-$(CONFIG_NUV_DECODER)             += nuv.o rtjpeg.o
> >   OBJS-$(CONFIG_ON2AVC_DECODER)          += on2avc.o on2avcdata.o
> >   OBJS-$(CONFIG_OPUS_DECODER)            += opusdec.o opus.o opus_celt.o
> opus_rc.o \
> > diff --git a/libavcodec/allcodecs.c b/libavcodec/allcodecs.c
> > index 628d27fd75..a30920bfe2 100644
> > --- a/libavcodec/allcodecs.c
> > +++ b/libavcodec/allcodecs.c
> > @@ -487,6 +487,8 @@ extern const AVCodec ff_mpc8_decoder;
> >   extern const AVCodec ff_msnsiren_decoder;
> >   extern const AVCodec ff_nellymoser_encoder;
> >   extern const AVCodec ff_nellymoser_decoder;
> > +extern const AVCodec ff_null_audio_encoder;
> > +extern const AVCodec ff_null_video_encoder;
> >   extern const AVCodec ff_on2avc_decoder;
> >   extern const AVCodec ff_opus_encoder;
> >   extern const AVCodec ff_opus_decoder;
> > diff --git a/libavcodec/codec_desc.c b/libavcodec/codec_desc.c
> > index 81f3b3c640..7d6bfd352c 100644
> > --- a/libavcodec/codec_desc.c
> > +++ b/libavcodec/codec_desc.c
> > @@ -3516,6 +3516,20 @@ static const AVCodecDescriptor
> codec_descriptors[] = {
> >           .long_name = NULL_IF_CONFIG_SMALL("AVFrame to AVPacket
> passthrough"),
> >           .props     = AV_CODEC_PROP_LOSSLESS,
> >       },
> > +    {
> > +        .id        = AV_CODEC_ID_AUDIO_NULL,
> > +        .type      = AVMEDIA_TYPE_AUDIO,
> > +        .name      = "null_audio",
> > +        .long_name = NULL_IF_CONFIG_SMALL("Audio NULL"),
> > +        .props     = AV_CODEC_PROP_LOSSY,
> > +    },
> > +    {
> > +        .id        = AV_CODEC_ID_VIDEO_NULL,
> > +        .type      = AVMEDIA_TYPE_VIDEO,
> > +        .name      = "null_video",
> > +        .long_name = NULL_IF_CONFIG_SMALL("Video NULL"),
> > +        .props     = AV_CODEC_PROP_LOSSY,
>
> Also AV_CODEC_PROP_INTRA_ONLY on both.
>
> > +    },
> >   };
> >
> >   static int descriptor_compare(const void *key, const void *member)
> > diff --git a/libavcodec/codec_id.h b/libavcodec/codec_id.h
> > index 3ffb9bd22e..4822dc7685 100644
> > --- a/libavcodec/codec_id.h
> > +++ b/libavcodec/codec_id.h
> > @@ -571,6 +571,8 @@ enum AVCodecID {
> >                                   * stream (only used by libavformat) */
> >       AV_CODEC_ID_FFMETADATA = 0x21000,   ///< Dummy codec for streams
> containing only metadata information.
> >       AV_CODEC_ID_WRAPPED_AVFRAME = 0x21001, ///< Passthrough codec,
> AVFrames wrapped in AVPacket
> > +    AV_CODEC_ID_AUDIO_NULL = 0x21002, ///< Null audio codec
> > +    AV_CODEC_ID_VIDEO_NULL = 0x21003, ///< Null video codec
> >   };
> >
> >   /**
> > diff --git a/libavcodec/nullenc.c b/libavcodec/nullenc.c
> > new file mode 100644
> > index 0000000000..8d3553ed33
> > --- /dev/null
> > +++ b/libavcodec/nullenc.c
> > @@ -0,0 +1,61 @@
> > +/*
> > + * Copyright (c) 2022 The FFmpeg Project
> > + *
> > + * This file is part of FFmpeg.
> > + *
> > + * FFmpeg is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU Lesser General Public
> > + * License as published by the Free Software Foundation; either
> > + * version 2.1 of the License, or (at your option) any later version.
> > + *
> > + * FFmpeg is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > + * Lesser General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU Lesser General Public
> > + * License along with FFmpeg; if not, write to the Free Software
> > + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
> 02110-1301 USA
> > + */
> > +
> > +#include "libavutil/internal.h"
> > +#include "libavutil/frame.h"
> > +#include "libavutil/buffer.h"
> > +
> > +#include "avcodec.h"
> > +#include "internal.h"
> > +#include "encode.h"
> > +
> > +static int null_encoder(AVCodecContext *avctx, AVPacket *pkt,
> > +                        const AVFrame *frame, int *got_packet)
> > +{
> > +    int ret;
> > +
> > +    pkt->pts = frame->pts;
> > +    if (avctx->codec_type == AVMEDIA_TYPE_AUDIO)
> > +        pkt->duration = ff_samples_to_time_base(avctx,
> frame->nb_samples);
> > +    pkt->flags |= AV_PKT_FLAG_KEY;
> > +    if ((ret = ff_alloc_packet(avctx, pkt, 1)) < 0)
>
> To avoid bogus statistics, could you instead allocate a blank packet of
> size av_samples_get_buffer_size()?
> Also, use ff_get_encode_buffer() and set the DR1 codec cap.
>
> > +        return ret;
> > +    *got_packet = 1;
> > +    return 0;
> > +}
> > +
> > +const AVCodec ff_null_video_encoder = {
> > +    .name           = "null_video",
> > +    .long_name      = NULL_IF_CONFIG_SMALL("Video NULL encoder"),
> > +    .type           = AVMEDIA_TYPE_VIDEO,
> > +    .id             = AV_CODEC_ID_VIDEO_NULL,
> > +    .encode2        = null_encoder,
> > +    .caps_internal  = FF_CODEC_CAP_INIT_THREADSAFE,
> > +};
> > +
> > +const AVCodec ff_null_audio_encoder = {
> > +    .name           = "null_audio",
> > +    .long_name      = NULL_IF_CONFIG_SMALL("Audio NULL encoder"),
> > +    .type           = AVMEDIA_TYPE_AUDIO,
> > +    .id             = AV_CODEC_ID_AUDIO_NULL,
> > +    .encode2        = null_encoder,
> > +    .caps_internal  = FF_CODEC_CAP_INIT_THREADSAFE,
> > +    .capabilities   = AV_CODEC_CAP_VARIABLE_FRAME_SIZE,
>
> What's the benefit from this? If the idea is to get rid of
> wrappedavframe, then you also need to fix vapoursync, decklink, kmsgrab,
> opengl, xv, and yuv4mpeg.
>
> I'd rather not add more fake codec ids for this purpose unless it's a
> thorough solution.
>

See null muxer patch. null muxer does not need pcm codecs or wrapped video
codec.


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