Re: [FFmpeg-devel] [PATCH 3/4] avformat/lc3: Add file format for LC3/LC3plus transport

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

On Thu, Mar 28, 2024 at 5:40 PM Antoine Soulier <asoulier@google.com> wrote:

> I don't think it's "easy" seekable.
> We cannot move to an arbitrary position:
> - There is no start-code
>

Not relevant.


> - The frame size can be variable (not generated by the proposed encoder
> implementation, but allowed).
>

Not relevant.


>
> The only possibility I see is checking that the frame size looks valid for
> multiple frames.
>

Not relevant, the only needed feature is known stored number of samples in
each packet for proper pts/timestamp generation.

The range of valid frame sizes is large (20 to 625 Bytes), so I can only
> validate 6 bits for each 16 bits packet size read.
>
> This format is not really designed to be seekable.
> Do you think we will need it?
>

I cant force you do to correct implementation.

Seeking is possible, just you are not aware of actual solution.
Hint: see other demuxers.


>
>
> On Thu, Mar 28, 2024 at 2:33 AM Paul B Mahol <onemda@gmail.com> wrote:
>
>> This format actually supports seeking.
>>
>> The proposed solution here is sub-optimal.
>>
>> On Wed, Mar 27, 2024 at 11:22 PM Antoine Soulier via ffmpeg-devel <
>> ffmpeg-devel@ffmpeg.org> wrote:
>>
>>> A file format is described in Bluetooth SIG LC3 and ETSI TS 103 634, for
>>> test purpose. This is the format implemented here.
>>>
>>> Signed-off-by: Antoine Soulier <asoulier@google.com>
>>> ---
>>>  doc/muxers.texi          |   6 ++
>>>  libavformat/Makefile     |   2 +
>>>  libavformat/allformats.c |   2 +
>>>  libavformat/lc3dec.c     | 135 +++++++++++++++++++++++++++++++++++++++
>>>  libavformat/lc3enc.c     | 102 +++++++++++++++++++++++++++++
>>>  5 files changed, 247 insertions(+)
>>>  create mode 100644 libavformat/lc3dec.c
>>>  create mode 100644 libavformat/lc3enc.c
>>>
>>> diff --git a/doc/muxers.texi b/doc/muxers.texi
>>> index a10a8e216f..9687746c30 100644
>>> --- a/doc/muxers.texi
>>> +++ b/doc/muxers.texi
>>> @@ -2612,6 +2612,12 @@ WebDAV server every second:
>>>  ffmpeg -f x11grab -framerate 1 -i :0.0 -q:v 6 -update 1 -protocol_opts
>>> method=PUT http://example.com/desktop.jpg
>>>  @end example
>>>
>>> +@section lc3
>>> +Bluetooth SIG Low Complexity Communication Codec audio (LC3), or
>>> +ETSI TS 103 634 Low Complexity Communication Codec plus (LC3plus).
>>> +
>>> +This muxer accepts a single @code{lc3} audio stream.
>>> +
>>>  @section matroska
>>>
>>>  Matroska container muxer.
>>> diff --git a/libavformat/Makefile b/libavformat/Makefile
>>> index 44aa485029..4961c42852 100644
>>> --- a/libavformat/Makefile
>>> +++ b/libavformat/Makefile
>>> @@ -332,6 +332,8 @@ OBJS-$(CONFIG_KVAG_DEMUXER)              += kvag.o
>>>  OBJS-$(CONFIG_KVAG_MUXER)                += kvag.o rawenc.o
>>>  OBJS-$(CONFIG_LAF_DEMUXER)               += lafdec.o
>>>  OBJS-$(CONFIG_LATM_MUXER)                += latmenc.o rawenc.o
>>> +OBJS-$(CONFIG_LC3_DEMUXER)               += lc3dec.o
>>> +OBJS-$(CONFIG_LC3_MUXER)                 += lc3enc.o
>>>  OBJS-$(CONFIG_LMLM4_DEMUXER)             += lmlm4.o
>>>  OBJS-$(CONFIG_LOAS_DEMUXER)              += loasdec.o rawdec.o
>>>  OBJS-$(CONFIG_LUODAT_DEMUXER)            += luodatdec.o
>>> diff --git a/libavformat/allformats.c b/libavformat/allformats.c
>>> index e15d0fa6d7..e225354faf 100644
>>> --- a/libavformat/allformats.c
>>> +++ b/libavformat/allformats.c
>>> @@ -252,6 +252,8 @@ extern const FFInputFormat  ff_kvag_demuxer;
>>>  extern const FFOutputFormat ff_kvag_muxer;
>>>  extern const FFInputFormat  ff_laf_demuxer;
>>>  extern const FFOutputFormat ff_latm_muxer;
>>> +extern const FFInputFormat  ff_lc3_demuxer;
>>> +extern const FFOutputFormat ff_lc3_muxer;
>>>  extern const FFInputFormat  ff_lmlm4_demuxer;
>>>  extern const FFInputFormat  ff_loas_demuxer;
>>>  extern const FFInputFormat  ff_luodat_demuxer;
>>> diff --git a/libavformat/lc3dec.c b/libavformat/lc3dec.c
>>> new file mode 100644
>>> index 0000000000..9ca9825f1b
>>> --- /dev/null
>>> +++ b/libavformat/lc3dec.c
>>> @@ -0,0 +1,135 @@
>>> +/*
>>> + * LC3 demuxer
>>> + * Copyright (C) 2024  Antoine Soulier <asoulier@google.com>
>>> + *
>>> + * 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
>>> + */
>>> +
>>> +/**
>>> + * @file
>>> + * Based on the file format specified by :
>>> + *
>>> + * - Bluetooth SIG - Low Complexity Communication Codec Test Suite
>>> + *
>>> https://www.bluetooth.org/docman/handlers/downloaddoc.ashx?doc_id=502301
>>> + *   3.2.8.2 Reference LC3 Codec Bitstream Format
>>> + *
>>> + * - ETSI TI 103 634 V1.4.1 - Low Complexity Communication Codec plus
>>> + *
>>> https://www.etsi.org/deliver/etsi_ts/103600_103699/103634/01.04.01_60/ts_103634v010401p.pdf
>>> + *   LC3plus conformance script package
>>> + */
>>> +
>>> +#include "libavcodec/packet.h"
>>> +#include "libavutil/intreadwrite.h"
>>> +
>>> +#include "avformat.h"
>>> +#include "avio.h"
>>> +#include "demux.h"
>>> +#include "internal.h"
>>> +
>>> +typedef struct LC3DemuxContext {
>>> +    int frame_samples;
>>> +    int64_t position;
>>> +    int64_t length;
>>> +} LC3DemuxContext;
>>> +
>>> +static int lc3_read_header(AVFormatContext *s)
>>> +{
>>> +    LC3DemuxContext *lc3 = s->priv_data;
>>> +    AVStream *st = NULL;
>>> +    uint16_t tag, hdr_size;
>>> +    uint16_t frame_us;
>>> +    uint32_t length;
>>> +    int ep_mode, hr_mode;
>>> +    int srate_hz, channels, bit_rate;
>>> +    int num_extra_params, ret;
>>> +
>>> +    tag = avio_rb16(s->pb);
>>> +    hdr_size = avio_rl16(s->pb);
>>> +
>>> +    if (tag != 0x1ccc || hdr_size < 9 * sizeof(uint16_t))
>>> +        return AVERROR_INVALIDDATA;
>>> +
>>> +    num_extra_params = hdr_size / sizeof(uint16_t) - 9;
>>> +
>>> +    srate_hz = avio_rl16(s->pb) * 100;
>>> +    bit_rate = avio_rl16(s->pb) * 100;
>>> +    channels = avio_rl16(s->pb);
>>> +    frame_us = avio_rl16(s->pb) * 10;
>>> +    ep_mode  = avio_rl16(s->pb) != 0;
>>> +    length   = avio_rl32(s->pb);
>>> +    hr_mode  = num_extra_params >= 1 && avio_rl16(s->pb);
>>> +
>>> +    st = avformat_new_stream(s, NULL);
>>> +    if (!st)
>>> +        return AVERROR(ENOMEM);
>>> +
>>> +    avpriv_set_pts_info(st, 32, 1, srate_hz);
>>> +    st->duration = length;
>>> +
>>> +    st->codecpar->codec_type = AVMEDIA_TYPE_AUDIO;
>>> +    st->codecpar->codec_id = AV_CODEC_ID_LC3;
>>> +    st->codecpar->sample_rate = srate_hz;
>>> +    st->codecpar->bit_rate = bit_rate;
>>> +    st->codecpar->ch_layout.nb_channels = channels;
>>> +
>>> +    if ((ret = ff_alloc_extradata(st->codecpar, 6)) < 0) {
>>> +        av_log(s, AV_LOG_ERROR, "Could not allocate extradata\n");
>>> +        return ret;
>>> +    }
>>> +
>>> +    AV_WL16(st->codecpar->extradata + 0, frame_us);
>>> +    AV_WL16(st->codecpar->extradata + 2, ep_mode);
>>> +    AV_WL16(st->codecpar->extradata + 4, hr_mode);
>>> +
>>> +    lc3->frame_samples = av_rescale(frame_us, srate_hz, 1000*1000);
>>> +
>>> +    lc3->position = 0;
>>> +    lc3->length = st->duration +
>>> +        av_rescale(frame_us == 7500 ? 4000 : 2500, srate_hz, 1000*1000);
>>> +
>>> +    return 0;
>>> +}
>>> +
>>> +static int lc3_read_packet(AVFormatContext *s, AVPacket *pkt)
>>> +{
>>> +    LC3DemuxContext *lc3 = s->priv_data;
>>> +    AVIOContext *pb = s->pb;
>>> +    int ret;
>>> +
>>> +    ret = av_get_packet(s->pb, pkt, avio_rl16(pb));
>>> +    if (ret < 0)
>>> +        return ret;
>>> +
>>> +    pkt->duration = lc3->frame_samples;
>>> +    lc3->position += lc3->frame_samples;
>>> +    if (lc3->position > lc3->length) {
>>> +        pkt->duration -= lc3->position - lc3->length;
>>> +        lc3->position = lc3->length;
>>> +    }
>>> +
>>> +    return 0;
>>> +}
>>> +
>>> +const FFInputFormat ff_lc3_demuxer = {
>>> +    .p.name         = "lc3",
>>> +    .p.long_name    = NULL_IF_CONFIG_SMALL("LC3 (Low Complexity
>>> Communication Codec)"),
>>> +    .p.extensions   = "lc3",
>>> +    .p.flags        = AVFMT_NOBINSEARCH | AVFMT_NOGENSEARCH |
>>> AVFMT_NO_BYTE_SEEK | AVFMT_NOTIMESTAMPS,
>>> +    .priv_data_size = sizeof(LC3DemuxContext),
>>> +    .read_header    = lc3_read_header,
>>> +    .read_packet    = lc3_read_packet,
>>> +};
>>> diff --git a/libavformat/lc3enc.c b/libavformat/lc3enc.c
>>> new file mode 100644
>>> index 0000000000..a7e3e3f4f7
>>> --- /dev/null
>>> +++ b/libavformat/lc3enc.c
>>> @@ -0,0 +1,102 @@
>>> +/*
>>> + * LC3 muxer
>>> + * Copyright (C) 2024  Antoine Soulier <asoulier@google.com>
>>> + *
>>> + * 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
>>> + */
>>> +
>>> +/**
>>> + * @file
>>> + * Based on the file format specified by :
>>> + *
>>> + * - Bluetooth SIG - Low Complexity Communication Codec Test Suite
>>> + *
>>> https://www.bluetooth.org/docman/handlers/downloaddoc.ashx?doc_id=502301
>>> + *   3.2.8.2 Reference LC3 Codec Bitstream Format
>>> + *
>>> + * - ETSI TI 103 634 V1.4.1 - Low Complexity Communication Codec plus
>>> + *
>>> https://www.etsi.org/deliver/etsi_ts/103600_103699/103634/01.04.01_60/ts_103634v010401p.pdf
>>> + *   LC3plus conformance script package
>>> + */
>>> +
>>> +#include "libavutil/intreadwrite.h"
>>> +
>>> +#include "avformat.h"
>>> +#include "avio.h"
>>> +#include "mux.h"
>>> +#include "internal.h"
>>> +
>>> +static av_cold int lc3_init(AVFormatContext *s)
>>> +{
>>> +    if (s->nb_streams != 1) {
>>> +        av_log(s, AV_LOG_ERROR, "This muxer only supports a single
>>> stream.\n");
>>> +        return AVERROR(EINVAL);
>>> +    }
>>> +
>>> +    return 0;
>>> +}
>>> +
>>> +static int lc3_write_header(AVFormatContext *s)
>>> +{
>>> +    AVStream *st = s->streams[0];
>>> +    int channels = st->codecpar->ch_layout.nb_channels;
>>> +    int srate_hz = st->codecpar->sample_rate;
>>> +    int bit_rate = st->codecpar->bit_rate;
>>> +    uint16_t frame_us = 10000;
>>> +    int ep_mode = 0, hr_mode = 0;
>>> +    uint32_t nb_samples = av_rescale_q(
>>> +        st->duration, st->time_base, (AVRational){ 1, srate_hz });
>>> +
>>> +    if (st->codecpar->extradata_size >= 2)
>>> +        frame_us = AV_RL16(st->codecpar->extradata + 0);
>>> +
>>> +    if (st->codecpar->extradata_size >= 6) {
>>> +        ep_mode = AV_RL16(st->codecpar->extradata + 2);
>>> +        hr_mode = AV_RL16(st->codecpar->extradata + 4);
>>> +    }
>>> +
>>> +    avio_wb16(s->pb, 0x1ccc);
>>> +    avio_wl16(s->pb, (9 + hr_mode) * sizeof(uint16_t));
>>> +    avio_wl16(s->pb, srate_hz / 100);
>>> +    avio_wl16(s->pb, bit_rate / 100);
>>> +    avio_wl16(s->pb, channels);
>>> +    avio_wl16(s->pb, frame_us / 10);
>>> +    avio_wl16(s->pb, ep_mode);
>>> +    avio_wl32(s->pb, nb_samples);
>>> +    if (hr_mode)
>>> +        avio_wl16(s->pb, hr_mode);
>>> +
>>> +    return 0;
>>> +}
>>> +
>>> +static int lc3_write_packet(AVFormatContext *s, AVPacket *pkt)
>>> +{
>>> +    avio_wl16(s->pb, pkt->size);
>>> +    avio_write(s->pb, pkt->data, pkt->size);
>>> +    return 0;
>>> +}
>>> +
>>> +const FFOutputFormat ff_lc3_muxer = {
>>> +    .p.name        = "lc3",
>>> +    .p.long_name   = NULL_IF_CONFIG_SMALL("LC3 (Low Complexity
>>> Communication Codec)"),
>>> +    .p.extensions  = "lc3",
>>> +    .p.audio_codec = AV_CODEC_ID_LC3,
>>> +    .p.video_codec = AV_CODEC_ID_NONE,
>>> +    .p.flags       = AVFMT_NOTIMESTAMPS,
>>> +    .init          = lc3_init,
>>> +    .write_header  = lc3_write_header,
>>> +    .write_packet  = lc3_write_packet,
>>> +};
>>> --
>>> 2.44.0.478.gd926399ef9-goog
>>>
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>>
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