Re: [FFmpeg-devel] [PATCH 2/2] avformat/lc3: Add file format for LC3/LC3plus transport

[Antoine Soulier via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

I am not sure about the block:

> +    lc3->timestamp += lc3->dt;
> +    if (lc3->timestamp > lc3->length) {
> +        pkt->duration -= lc3->timestamp - lc3->length;
> +        lc3->timestamp = lc3->length;
> +    }


The purpose is to reduce the duration of the last packet.
When converting a file, the last frame can contain "zeros" (or irrelevant)
samples that are not present in the source file (alignment to frame
boundary). These samples should be discarded.
> If I remove the "read_seek()" implementation, I lose the PTS / timestamp
information, and I don't know how to detect the last frame in the stream.
Do you know how I can handle a reduced duration for the last frame without
having an implementation of "read_seek()"?

(I can play with the position and EOF information, but can lead to strange
behaviors if the encoder adds extra frames at the end).


On Sat, Mar 30, 2024 at 4:46 AM Paul B Mahol <onemda@gmail.com> wrote:

>
>
> On Fri, Mar 29, 2024 at 6:30 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>
>> ---
>>  Changelog                |   1 +
>>  doc/muxers.texi          |   6 ++
>>  libavformat/Makefile     |   2 +
>>  libavformat/allformats.c |   2 +
>>  libavformat/lc3dec.c     | 164 +++++++++++++++++++++++++++++++++++++++
>>  libavformat/lc3enc.c     | 100 ++++++++++++++++++++++++
>>  6 files changed, 275 insertions(+)
>>  create mode 100644 libavformat/lc3dec.c
>>  create mode 100644 libavformat/lc3enc.c
>>
>> diff --git a/Changelog b/Changelog
>> index 83a4cf7888..08c200a41d 100644
>> --- a/Changelog
>> +++ b/Changelog
>> @@ -2,6 +2,7 @@ Entries are sorted chronologically from oldest to
>> youngest within each release,
>>  releases are sorted from youngest to oldest.
>>
>>  version <next>:
>> +- LC3/LC3plus demuxer and muxer
>>  - LC3/LC3plus decoding/encoding using external library liblc3
>>
>>
>> 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 9df42bb87a..0b36a7c3eb 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..74d6794d00
>> --- /dev/null
>> +++ b/libavformat/lc3dec.c
>> @@ -0,0 +1,164 @@
>> +/*
>> + * 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 dt, delay;
>> +    int64_t timestamp;
>> +    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_10us;
>> +    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_10us = avio_rl16(s->pb);
>> +    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, 64, 1, srate_hz);
>> +    st->start_time = 0;
>> +    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_10us);
>> +    AV_WL16(st->codecpar->extradata + 2, ep_mode);
>> +    AV_WL16(st->codecpar->extradata + 4, hr_mode);
>> +
>> +    lc3->dt = av_rescale(frame_10us, srate_hz, 100*1000);
>> +    lc3->delay = av_rescale(frame_10us == 750 ? 400 : 250, srate_hz,
>> 100*1000);
>> +
>> +    lc3->timestamp = -lc3->delay;
>> +    lc3->length = st->duration;
>> +
>> +    return 0;
>> +}
>> +
>> +static int lc3_read_packet(AVFormatContext *s, AVPacket *pkt)
>> +{
>> +    LC3DemuxContext *lc3 = s->priv_data;
>> +    AVIOContext *pb = s->pb;
>> +    int ret;
>> +
>>
>
> int64_t pos = avio_tell(pb);
>
>
>> +    ret = av_get_packet(s->pb, pkt, avio_rl16(pb));
>> +    if (ret < 0)
>> +        return ret;
>> +
>> +    pkt->pos -= 2;
>>
>
> pkt->pos = pos;
>
> +    pkt->pts = FFMAX(lc3->timestamp, 0);
>>
>
> Remove that line above.
>
>
>> +    pkt->duration = lc3->dt;
>> +
>> +    lc3->timestamp += lc3->dt;
>> +    if (lc3->timestamp > lc3->length) {
>> +        pkt->duration -= lc3->timestamp - lc3->length;
>> +        lc3->timestamp = lc3->length;
>> +    }
>> +
>>
>
> Remove above block.
>
>
>> +    return 0;
>> +}
>> +
>> +static int lc3_read_seek(AVFormatContext *s, int stream_index, int64_t
>> timestamp, int flags)
>> +{
>> +    AVStream *st = s->streams[stream_index];
>> +    FFStream *const sti = ffstream(st);
>> +    LC3DemuxContext *lc3 = s->priv_data;
>> +    const AVIndexEntry *ie;
>> +    int index;
>> +
>> +    timestamp = FFMAX(timestamp - lc3->delay, 0);
>> +    if (timestamp >= lc3->length)
>> +        return AVERROR_EOF;
>> +
>> +    index = av_index_search_timestamp(st, timestamp, flags);
>> +    ie = index < 0 ? NULL : &sti->index_entries[index];
>> +    if (!ie || avio_seek(s->pb, ie->pos, SEEK_SET) < 0)
>> +        return -1;
>> +
>> +    lc3->timestamp = ie->timestamp;
>> +    if (lc3->timestamp == 0)
>> +      lc3->timestamp -= lc3->delay;
>> +
>> +    return 0;
>> +}
>>
>
> This logic is unnecessary.
> Format does not store timestamp internally in bitstream.
> Just set packet duration to number of samples stored in that packet.
> No need for pts overdesign, and remove this read_seek_function.
> And just leave GENERIC_INDEX flags bellow.
>
>
>> +
>> +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_GENERIC_INDEX,
>> +    .priv_data_size = sizeof(LC3DemuxContext),
>> +    .read_header    = lc3_read_header,
>> +    .read_packet    = lc3_read_packet,
>> +    .read_seek      = lc3_read_seek,
>> +};
>> diff --git a/libavformat/lc3enc.c b/libavformat/lc3enc.c
>> new file mode 100644
>> index 0000000000..e768212f63
>> --- /dev/null
>> +++ b/libavformat/lc3enc.c
>> @@ -0,0 +1,100 @@
>> +/*
>> + * 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;
>> +    int frame_us, ep_mode, hr_mode;
>> +    uint32_t nb_samples = av_rescale_q(
>> +        st->duration, st->time_base, (AVRational){ 1, srate_hz });
>> +
>> +    if (st->codecpar->extradata_size < 6)
>> +        return AVERROR_INVALIDDATA;
>> +
>> +    frame_us = AV_RL16(st->codecpar->extradata + 0) * 10;
>> +    ep_mode = AV_RL16(st->codecpar->extradata + 2) != 0;
>> +    hr_mode = AV_RL16(st->codecpar->extradata + 4) != 0;
>> +
>> +    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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