[FFmpeg-devel] [PATCH] apedec: add ability to check CRC

[James Almer]

On 3/6/2019 8:22 AM, Lynne wrote:
> The CRC flag is only signalled once every few minutes but CRC is still
> always present so the patch uses the file version instead.
> CRC on 24-bit files wants non-padded samples so skip such files.
> Some corrupt samples may have been output before the final check
> depending on the -max_samples setting.
> 
> 
> 0001-apedec-add-ability-to-check-CRC.patch
> 
> From ad5773274448c209371dc8c70b4b21f39f968308 Mon Sep 17 00:00:00 2001
> From: Lynne <dev at lynne.ee>
> Date: Wed, 6 Mar 2019 11:01:01 +0000
> Subject: [PATCH] apedec: add ability to check CRC
> 
> The CRC flag is only signalled once every few minutes but CRC is still
> always present so the patch uses the file version instead.
> CRC on 24-bit files wants non-padded samples so skip such files.
> Some corrupt samples may have been output before the final check
> depending on the -max_samples setting.
> ---
>  libavcodec/apedec.c | 25 ++++++++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/apedec.c b/libavcodec/apedec.c
> index 15eb416ba4..3208275f6e 100644
> --- a/libavcodec/apedec.c
> +++ b/libavcodec/apedec.c
> @@ -24,6 +24,7 @@
>  
>  #include "libavutil/avassert.h"
>  #include "libavutil/channel_layout.h"
> +#include "libavutil/crc.h"
>  #include "libavutil/opt.h"
>  #include "lossless_audiodsp.h"
>  #include "avcodec.h"
> @@ -147,7 +148,8 @@ typedef struct APEContext {
>      int fset;                                ///< which filter set to use (calculated from compression level)
>      int flags;                               ///< global decoder flags
>  
> -    uint32_t CRC;                            ///< frame CRC
> +    uint32_t CRC;                            ///< signalled frame CRC
> +    uint32_t CRC_state;                      ///< accumulated CRC
>      int frameflags;                          ///< frame flags
>      APEPredictor predictor;                  ///< predictor used for final reconstruction
>  
> @@ -730,6 +732,7 @@ static int init_entropy_decoder(APEContext *ctx)
>  
>      /* Read the frame flags if they exist */
>      ctx->frameflags = 0;
> +    ctx->CRC_state = ~0U;

nit: UINT32_MAX.

>      if ((ctx->fileversion > 3820) && (ctx->CRC & 0x80000000)) {
>          ctx->CRC &= ~0x80000000;
>  
> @@ -1548,6 +1551,26 @@ static int ape_decode_frame(AVCodecContext *avctx, void *data,
>  
>      s->samples -= blockstodecode;
>  
> +    if ((avctx->err_recognition & (AV_EF_CRCCHECK | AV_EF_COMPLIANT)) &&
> +        (s->fileversion >= 3900) && (s->bps < 24)) {
> +        uint32_t crc = s->CRC_state;
> +        const AVCRC *crc_tab = av_crc_get_table(AV_CRC_32_IEEE_LE);
> +        for (i = 0; i < blockstodecode; i++) {
> +            for (ch = 0; ch < s->channels; ch++) {
> +                uint8_t *smp = frame->data[ch] + (i*(s->bps >> 3));
> +                crc = av_crc(crc_tab, crc, smp, s->bps >> 3);
> +            }
> +        }
> +
> +        if (!s->samples && ((~crc >> 1) ^ s->CRC)) {
> +            av_log(avctx, AV_LOG_ERROR, "CRC mismatch! Previously decoded "
> +                   "frames may have been affected as well.\n");
> +            return AVERROR_INVALIDDATA;

Abort with an error only if (avctx->err_recognition & AV_EF_EXPLODE) is
true.

> +        }
> +
> +        s->CRC_state = crc;
> +    }
> +
>      *got_frame_ptr = 1;
>  
>      return !s->samples ? avpkt->size : 0;
> -- 2.21.0
> 
> 
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