Re: [FFmpeg-devel] [PATCH v2 1/2] avcodec/aac_ac3_parser: remove dead code

From: James Almer <jamrial-at-gmail.com@ffmpeg.org>
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH v2 1/2] avcodec/aac_ac3_parser: remove dead code
Date: Mon, 7 Jul 2025 10:40:52 -0300
Message-ID: <bdb973a4-ede0-49cf-929d-a4c28ead3e09@gmail.com> (raw)
In-Reply-To: <20250707131930.2924213-1-nicolas.gaullier@cji.paris>

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On 7/7/2025 10:19 AM, Nicolas Gaullier wrote:
> ff_adts_header_parse() gets the object_type from only 2 bits.
> See also 696ea1c2236842572df88d573e24a39be3f19c98.
> 
> Introduced in 64bb91fd3b5a00a8849531c7e8dd207f2a626096.
> 
> Signed-off-by: Nicolas Gaullier <nicolas.gaullier@cji.paris>
> ---
>   libavcodec/aac_ac3_parser.c | 7 +++----
>   1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/libavcodec/aac_ac3_parser.c b/libavcodec/aac_ac3_parser.c
> index e10ce13a3b..b49ce0277c 100644
> --- a/libavcodec/aac_ac3_parser.c
> +++ b/libavcodec/aac_ac3_parser.c
> @@ -147,15 +147,14 @@ get_next:
>           } else {
>   #if CONFIG_AAC_PARSER
>               AACADTSHeaderInfo hdr;
> -            GetBitContext gb;
>   
> -            init_get_bits8(&gb, buf, buf_size);
>               if (buf_size < AV_AAC_ADTS_HEADER_SIZE ||
> -                ff_adts_header_parse(&gb, &hdr) < 0)
> +                ff_adts_header_parse_buf(buf, &hdr) < 0)
>                   return i;
>   
>               avctx->profile = hdr.object_type - 1;
> -            s1->key_frame = (avctx->profile == AV_PROFILE_AAC_USAC) ? get_bits1(&gb) : 1;
> +            /* ADTS does not support USAC */
> +            s1->key_frame = 1;
>               bit_rate = hdr.bit_rate;
>   #endif
>           }

This isn't dead code. It just moves the getbitcontext creation to the 
wrapper function ff_adts_header_parse_buf().

Also, the buffer needs AV_INPUT_BUFFER_PADDING_SIZE of padding bytes, so 
maybe use a zeroed local buffer while at it and memcpy 
AV_AAC_ADTS_HEADER_SIZE bytes to it, then pass that.

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