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

[James Almer <jamrial@gmail.com>]

On 3/14/2022 9:17 AM, Paul B Mahol wrote:
> 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.

I saw it, hence my comment above. wrappedavframe is still used by 
several components, so this is adding two new pseudo codec ids but not 
resolving the problem wrappedavframes represents.
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