Re: [FFmpeg-devel] [PATCH 5/6] avformat/movenc: utilize existing AC-3 parsing workflow for AC-3

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Jan Ekström:
> From: Jan Ekström <jan.ekstrom@24i.com>
> 
> Signed-off-by: Jan Ekström <jan.ekstrom@24i.com>
> ---
>  libavformat/Makefile          |  1 +
>  libavformat/ac3_bitrate_tab.c | 22 ++++++++++++++
>  libavformat/movenc.c          | 55 +++++++++++++++++------------------
>  3 files changed, 50 insertions(+), 28 deletions(-)
>  create mode 100644 libavformat/ac3_bitrate_tab.c
> 
> diff --git a/libavformat/Makefile b/libavformat/Makefile
> index 1416bf31bd..c71de95b2f 100644
> --- a/libavformat/Makefile
> +++ b/libavformat/Makefile
> @@ -699,6 +699,7 @@ SHLIBOBJS-$(CONFIG_FLV_MUXER)            += mpeg4audio_sample_rates.o
>  SHLIBOBJS-$(CONFIG_HLS_DEMUXER)          += ac3_channel_layout_tab.o
>  SHLIBOBJS-$(CONFIG_MATROSKA_DEMUXER)     += mpeg4audio_sample_rates.o
>  SHLIBOBJS-$(CONFIG_MOV_DEMUXER)          += ac3_channel_layout_tab.o
> +SHLIBOBJS-$(CONFIG_MOV_MUXER)            += ac3_bitrate_tab.o
>  SHLIBOBJS-$(CONFIG_MP3_MUXER)            += mpegaudiotabs.o
>  SHLIBOBJS-$(CONFIG_MXF_MUXER)            += golomb_tab.o
>  SHLIBOBJS-$(CONFIG_NUT_MUXER)            += mpegaudiotabs.o

The above line only takes care of duplicating ac3_bitrate_tab.o into
lavf for shared builds; yet there needs to be a corresponding STLIBOBJS
entry in lavc/Makefile so that lavc/ac3_bitrate_tab.o is compiled in
case the mov muxer is enabled in a static build.
It would work either way in this case because #2 made the mov muxer
depend upon the ac3 parser which makes lavc/ac3_bitrate_tab.o be included.

> diff --git a/libavformat/ac3_bitrate_tab.c b/libavformat/ac3_bitrate_tab.c
> new file mode 100644
> index 0000000000..57b6181511
> --- /dev/null
> +++ b/libavformat/ac3_bitrate_tab.c
> @@ -0,0 +1,22 @@
> +/*
> + * AC-3 bit rate table
> + * copyright (c) 2001 Fabrice Bellard
> + *
> + * 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 "libavcodec/ac3_bitrate_tab.h"
> diff --git a/libavformat/movenc.c b/libavformat/movenc.c
> index 103f958d75..a071f1cdd5 100644
> --- a/libavformat/movenc.c
> +++ b/libavformat/movenc.c
> @@ -36,6 +36,7 @@
>  #include "av1.h"
>  #include "avc.h"
>  #include "libavcodec/ac3_parser_internal.h"
> +#include "libavcodec/ac3tab.h"
>  #include "libavcodec/dnxhddata.h"
>  #include "libavcodec/flac.h"
>  #include "libavcodec/get_bits.h"
> @@ -362,44 +363,42 @@ struct eac3_info {
>  
>  static int mov_write_ac3_tag(AVFormatContext *s, AVIOContext *pb, MOVTrack *track)
>  {
> -    GetBitContext gbc;
> +    struct eac3_info *info = track->eac3_priv;
> +    int8_t ac3_bit_rate_code = -1;
>      PutBitContext pbc;
>      uint8_t buf[3];
> -    int fscod, bsid, bsmod, acmod, lfeon, frmsizecod;
>  
> -    if (track->vos_len < 7) {
> +    if (!info || !info->ec3_done) {
>          av_log(s, AV_LOG_ERROR,
>                 "Cannot write moov atom before AC3 packets."
>                 " Set the delay_moov flag to fix this.\n");
>          return AVERROR(EINVAL);
>      }
>  
> -    avio_wb32(pb, 11);
> -    ffio_wfourcc(pb, "dac3");
> +    for (unsigned int i = 0; i < FF_ARRAY_ELEMS(ff_ac3_bitrate_tab); i++) {
> +        if (info->data_rate == ff_ac3_bitrate_tab[i]) {
> +            ac3_bit_rate_code = i;

Anyway, I see that you use ff_ac3_bitrate_tab in lavf instead of adding
the frame_size_code to AC3HeaderInfo. Did it turn out to be easier this
way or what is the reason for this?

> +            break;
> +        }
> +    }
>  
> -    init_get_bits(&gbc, track->vos_data + 4, (track->vos_len - 4) * 8);
> -    fscod      = get_bits(&gbc, 2);
> -    frmsizecod = get_bits(&gbc, 6);
> -    bsid       = get_bits(&gbc, 5);
> -    bsmod      = get_bits(&gbc, 3);
> -    acmod      = get_bits(&gbc, 3);
> -    if (acmod == 2) {
> -        skip_bits(&gbc, 2); // dsurmod
> -    } else {
> -        if ((acmod & 1) && acmod != 1)
> -            skip_bits(&gbc, 2); // cmixlev
> -        if (acmod & 4)
> -            skip_bits(&gbc, 2); // surmixlev
> +    if (ac3_bit_rate_code < 0) {
> +        av_log(s, AV_LOG_ERROR,
> +               "No valid AC3 bit rate code for data rate of %d!\n",
> +               info->data_rate);
> +        return AVERROR(EINVAL);
>      }
> -    lfeon = get_bits1(&gbc);
> +
> +    avio_wb32(pb, 11);
> +    ffio_wfourcc(pb, "dac3");
>  
>      init_put_bits(&pbc, buf, sizeof(buf));
> -    put_bits(&pbc, 2, fscod);
> -    put_bits(&pbc, 5, bsid);
> -    put_bits(&pbc, 3, bsmod);
> -    put_bits(&pbc, 3, acmod);
> -    put_bits(&pbc, 1, lfeon);
> -    put_bits(&pbc, 5, frmsizecod >> 1); // bit_rate_code
> +    put_bits(&pbc, 2, info->substream[0].fscod);
> +    put_bits(&pbc, 5, info->substream[0].bsid);
> +    put_bits(&pbc, 3, info->substream[0].bsmod);
> +    put_bits(&pbc, 3, info->substream[0].acmod);
> +    put_bits(&pbc, 1, info->substream[0].lfeon);
> +    put_bits(&pbc, 5, ac3_bit_rate_code); // bit_rate_code
>      put_bits(&pbc, 5, 0); // reserved
>  
>      flush_put_bits(&pbc);
> @@ -5975,8 +5974,7 @@ int ff_mov_write_packet(AVFormatContext *s, AVPacket *pkt)
>      if ((par->codec_id == AV_CODEC_ID_DNXHD ||
>           par->codec_id == AV_CODEC_ID_H264 ||
>           par->codec_id == AV_CODEC_ID_HEVC ||
> -         par->codec_id == AV_CODEC_ID_TRUEHD ||
> -         par->codec_id == AV_CODEC_ID_AC3) && !trk->vos_len &&
> +         par->codec_id == AV_CODEC_ID_TRUEHD) && !trk->vos_len &&
>           !TAG_IS_AVCI(trk->tag)) {
>          /* copy frame to create needed atoms */
>          trk->vos_len  = size;
> @@ -6053,7 +6051,8 @@ int ff_mov_write_packet(AVFormatContext *s, AVPacket *pkt)
>              }
>          }
>  
> -    } else if (par->codec_id == AV_CODEC_ID_EAC3) {
> +    } else if (par->codec_id == AV_CODEC_ID_EAC3 ||
> +               par->codec_id == AV_CODEC_ID_AC3) {
>          size = handle_eac3(mov, pkt, trk);
>          if (size < 0)
>              return size;

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