[FFmpeg-devel] [PATCH 2/2] avformat/westwoodaudenc Adds muxer for Westwood AUD format.

[Andreas Rheinhardt]

Aidan Richmond:
> Format is still used by modders of these old games.
> ---
>  libavformat/Makefile          |   1 +
>  libavformat/allformats.c      |   1 +
>  libavformat/westwood_audenc.c | 120 ++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 122 insertions(+)
>  create mode 100644 libavformat/westwood_audenc.c
> 
> diff --git a/libavformat/Makefile b/libavformat/Makefile
> index bc1ddfa81c..85b5d8e7eb 100644
> --- a/libavformat/Makefile
> +++ b/libavformat/Makefile
> @@ -581,6 +581,7 @@ OBJS-$(CONFIG_WEBP_MUXER)                += webpenc.o
>  OBJS-$(CONFIG_WEBVTT_DEMUXER)            += webvttdec.o subtitles.o
>  OBJS-$(CONFIG_WEBVTT_MUXER)              += webvttenc.o
>  OBJS-$(CONFIG_WSAUD_DEMUXER)             += westwood_aud.o
> +OBJS-$(CONFIG_WSAUD_MUXER)               += westwood_audenc.o
>  OBJS-$(CONFIG_WSD_DEMUXER)               += wsddec.o rawdec.o
>  OBJS-$(CONFIG_WSVQA_DEMUXER)             += westwood_vqa.o
>  OBJS-$(CONFIG_WTV_DEMUXER)               += wtvdec.o wtv_common.o \
> diff --git a/libavformat/allformats.c b/libavformat/allformats.c
> index fa093c7ac2..fe70a1e9a2 100644
> --- a/libavformat/allformats.c
> +++ b/libavformat/allformats.c
> @@ -478,6 +478,7 @@ extern AVOutputFormat ff_webp_muxer;
>  extern AVInputFormat  ff_webvtt_demuxer;
>  extern AVOutputFormat ff_webvtt_muxer;
>  extern AVInputFormat  ff_wsaud_demuxer;
> +extern AVOutputFormat ff_wsaud_muxer;
>  extern AVInputFormat  ff_wsd_demuxer;
>  extern AVInputFormat  ff_wsvqa_demuxer;
>  extern AVInputFormat  ff_wtv_demuxer;
> diff --git a/libavformat/westwood_audenc.c b/libavformat/westwood_audenc.c
> new file mode 100644
> index 0000000000..49310a47c8
> --- /dev/null
> +++ b/libavformat/westwood_audenc.c
> @@ -0,0 +1,120 @@
> +/*
> + * Copyright (c) 2021 Aidan Richmond
> + *
> + * 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
> + * Westwood Studios AUD file muxer
> + * by Aidan Richmond (aidan.is at hotmail.co.uk)
> + * 
> + * This muxer supports IMA ADPCM packed in westwoods format.
> + * 
> + * @see http://xhp.xwis.net/documents/aud3.txt
> + */
> +
> +#include "avformat.h"
> +#include "internal.h"
> +
> +#define AUD_CHUNK_SIGNATURE 0x0000DEAF
> +
> +typedef struct AUDMuxContext {
> +    int uncomp_size;
> +    int size;
> +} AUDMuxContext;
> +
> +static int wsaud_write_header(AVFormatContext *ctx)
> +{
> +    AVStream      *s = ctx->streams[0];

We typically use st for AVStream (and s is (for some reason used for
AVFormatContext).

> +    AVIOContext  *pb = ctx->pb;
> +    AUDMuxContext *a = ctx->priv_data;
> +    unsigned char flags = 0;
> +
> +    if (s->codecpar->codec_id != AV_CODEC_ID_ADPCM_IMA_WS) {
> +        AVCodec *codec = avcodec_find_decoder(ctx->streams[0]->codecpar->codec_id);

Use avcodec_get_name() directly. Furthermore use

> +        av_log(s, AV_LOG_ERROR, "%s codec not supported for Westwood AUD.\n",
> +               codec ? codec->name : "NONE");
> +        return -1;
> +    }
> +
> +    if (ctx->nb_streams != 1) {
> +        av_log(s, AV_LOG_ERROR, "AUD files have exactly one stream\n");
> +        return AVERROR(EINVAL);
> +    }
> +
> +    a->uncomp_size = 0;
> +    a->size = 0;
> +
> +    /* Flag if we have stereo data. */
> +    if (s->codecpar->channels == 2)
> +        flags |= 1;
> +    
> +    /* This flags that the file contains 16 bit samples rather than 8 bit
> +       since the encoder only encodes 16 bit samples this should be set. */
> +    flags |= 2;

You presume that libavformat is only used in conjunction with the
current libavcodec version. But the packets might come from another
encoder or a future version of libavcodec. I presume the information
about the bitness is contained in codecpar->bits_per_raw_sample or so.

> +
> +    avio_wl16(pb, s->codecpar->sample_rate);
> +    /* We don't know the file size yet, so just skip forward 8 bytes */
> +    avio_seek(pb, 8, SEEK_CUR);

Then just zero this field.

> +    avio_w8(pb, flags);
> +    /* 99 indicates the ADPCM format. Other formats not supported. */
> +    avio_w8(pb, 99);
> +
> +    return 0;
> +}
> +
> +static int wsaud_write_packet(AVFormatContext *ctx, AVPacket *pkt)
> +{
> +    AVIOContext  *pb = ctx->pb;
> +    AUDMuxContext *a = ctx->priv_data;
> +    
> +    /* Assumes ADPCM since this muxer doesn't support SND1 or PCM format. */
> +    avio_wl16(pb, pkt->size);
> +    avio_wl16(pb, pkt->size * 4);

You need to check that this indeed fits into an uint16_t.

> +    avio_wl32(pb, AUD_CHUNK_SIGNATURE);
> +    avio_write(pb, pkt->data, pkt->size);
> +    a->size += pkt->size + 8;
> +    a->uncomp_size += pkt->size * 4;
> +
> +    return 0;
> +}
> +
> +static int wsaud_write_trailer(AVFormatContext *ctx)
> +{
> +    AVIOContext  *pb = ctx->pb;
> +    AUDMuxContext *a = ctx->priv_data;
> +
> +    avio_seek(pb, 2, SEEK_SET);

Don't just seek, check whether the file is seekable first. Otherwise you
will write junk at the end of the output.

> +    avio_wl32(pb, a->size);
> +    avio_wl32(pb, a->uncomp_size);
> +
> +    return 0;
> +}
> +
> +AVOutputFormat ff_wsaud_muxer = {
> +    .name              = "wsaud",
> +    .long_name         = NULL_IF_CONFIG_SMALL("Westwood Studios audio"),
> +    .extensions        = "aud",
> +    .priv_data_size    = sizeof(AUDMuxContext),
> +    .audio_codec       = AV_CODEC_ID_ADPCM_IMA_WS,
> +    .video_codec       = AV_CODEC_ID_NONE,
> +    .flags             = AVFMT_TS_NONSTRICT,
> +    .write_header      = wsaud_write_header,
> +    .write_packet      = wsaud_write_packet,
> +    .write_trailer     = wsaud_write_trailer,
> +};
>