[FFmpeg-devel] [PATCH 2/2] libavcodec/ac3_parser: add avpriv function to parse EC3SpecificBox (dec3)

[Nachiket Tarate]

So you want me to change ff_ac3_sample_rate_tab to avpriv_ac3_sample_rate_tab and get channel count using av_get_channel_layout_nb_channels(). Is my understanding correct ?
________________________________
From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> on behalf of James Almer <jamrial at gmail.com>
Sent: Saturday, October 3, 2020 11:04 PM
To: ffmpeg-devel at ffmpeg.org <ffmpeg-devel at ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 2/2] libavcodec/ac3_parser: add avpriv function to parse EC3SpecificBox (dec3)

On 10/3/2020 2:30 PM, Nachiket Tarate wrote:
> Actually names of 2 tables ff_ac3_sample_rate_tab and ff_ac3_channels_tab need to be changed in order to access them from libavformat.
> There would be changes in multiple files in which these tables have been used currently. Is that fine ?

You can use av_get_channel_layout_nb_channels() to get channel count
from the output of avpriv_ac3_channel_layout_tab[]. Same as
mov_read_dec3() in libavformat/mov.c does.

>
> ________________________________
> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> on behalf of James Almer <jamrial at gmail.com>
> Sent: Friday, October 2, 2020 7:48 PM
> To: ffmpeg-devel at ffmpeg.org <ffmpeg-devel at ffmpeg.org>
> Subject: Re: [FFmpeg-devel] [PATCH 2/2] libavcodec/ac3_parser: add avpriv function to parse EC3SpecificBox (dec3)
>
> On 10/2/2020 10:10 AM, Nachiket Tarate wrote:
>> This will be used by HLS demuxer for SAMPLE-AES decryption.
>>
>> Signed-off-by: Nachiket Tarate <nachiket.tarate at outlook.com>
>> ---
>>  libavcodec/ac3_parser.c          | 47 ++++++++++++++++++++++++++++++++
>>  libavcodec/ac3_parser_internal.h |  4 +++
>>  2 files changed, 51 insertions(+)
>>
>> diff --git a/libavcodec/ac3_parser.c b/libavcodec/ac3_parser.c
>> index ba171653ef..a8fdde0ff9 100644
>> --- a/libavcodec/ac3_parser.c
>> +++ b/libavcodec/ac3_parser.c
>> @@ -2,6 +2,7 @@
>>   * AC-3 parser
>>   * Copyright (c) 2003 Fabrice Bellard
>>   * Copyright (c) 2003 Michael Niedermayer
>> + * Copyright (c) 2020 Nachiket Tarate
>>   *
>>   * This file is part of FFmpeg.
>>   *
>> @@ -172,6 +173,47 @@ int avpriv_ac3_parse_header(AC3HeaderInfo **phdr, const uint8_t *buf,
>>      return get_bits_count(&gb);
>>  }
>>
>> +/*
>> + * Parse 'dec3' EC3SpecificBox
>> + */
>> +int avpriv_eac3_parse_dec3(AC3HeaderInfo **phdr, const uint8_t *buf, size_t size)
>> +{
>> +    GetBitContext gb;
>> +    AC3HeaderInfo *hdr;
>> +    int err;
>> +
>> +    int data_rate, fscod, acmod, lfeon;
>> +
>> +    if (!*phdr)
>> +        *phdr = av_mallocz(sizeof(AC3HeaderInfo));
>> +    if (!*phdr)
>> +        return AVERROR(ENOMEM);
>> +    hdr = *phdr;
>> +
>> +    err = init_get_bits8(&gb, buf, size);
>> +    if (err < 0)
>> +        return AVERROR_INVALIDDATA;
>> +
>> +    data_rate = get_bits(&gb, 13);
>> +    skip_bits(&gb, 3);
>> +    fscod = get_bits(&gb, 2);
>> +    skip_bits(&gb, 10);
>> +    acmod = get_bits(&gb, 3);
>> +    lfeon = get_bits(&gb, 1);
>> +
>> +    hdr->sample_rate = ff_ac3_sample_rate_tab[fscod];
>
> Why not instead just make this array avpriv_? Everything else can be
> done within libavformat. See mov_read_dec3() in mov.c
>
>> +
>> +    hdr->channels = ff_ac3_channels_tab[acmod] + lfeon;
>> +
>> +    hdr->channel_layout = avpriv_ac3_channel_layout_tab[acmod];
>> +    if (lfeon)
>> +        hdr->channel_layout |= AV_CH_LOW_FREQUENCY;
>> +
>> +    hdr->bit_rate = data_rate*1000;
>> +
>> +    return 0;
>> +}
>> +
>>  int av_ac3_parse_header(const uint8_t *buf, size_t size,
>>                          uint8_t *bitstream_id, uint16_t *frame_size)
>>  {
>> @@ -256,6 +298,11 @@ int avpriv_ac3_parse_header(AC3HeaderInfo **phdr, const uint8_t *buf,
>>      return AVERROR(ENOSYS);
>>  }
>>
>> +int avpriv_eac3_parse_dec3(AC3HeaderInfo **phdr, const uint8_t *buf, size_t size)
>> +{
>> +    return AVERROR(ENOSYS);
>> +}
>> +
>>  int av_ac3_parse_header(const uint8_t *buf, size_t size,
>>                          uint8_t *bitstream_id, uint16_t *frame_size)
>>  {
>> diff --git a/libavcodec/ac3_parser_internal.h b/libavcodec/ac3_parser_internal.h
>> index 3648802a73..0388a5bb5e 100644
>> --- a/libavcodec/ac3_parser_internal.h
>> +++ b/libavcodec/ac3_parser_internal.h
>> @@ -38,5 +38,9 @@ int ff_ac3_parse_header(GetBitContext *gbc, AC3HeaderInfo *hdr);
>>
>>  int avpriv_ac3_parse_header(AC3HeaderInfo **hdr, const uint8_t *buf,
>>                              size_t size);
>> +/*
>> + * Parse 'dec3' EC3SpecificBox
>> + */
>> +int avpriv_eac3_parse_dec3(AC3HeaderInfo **phdr, const uint8_t *buf, size_t size);
>>
>>  #endif /* AVCODEC_AC3_PARSER_INTERNAL_H */
>>
>
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