[FFmpeg-devel] [PATCH v16 05/15] lavc/jpegtables: Handle multiple mappings to the same value

[Michael Niedermayer]

On Wed, Aug 28, 2019 at 03:27:13PM +0300, Nick Renieris wrote:
> From: Nick Renieris <velocityra at gmail.com>
> 
> Some JPEGs [1] have incorrect DHT entries that map 2 codes to
> the same value.
> 
> The second (last) mapping does not ever actually appear in the
> code stream, therefore ignoring any mappings after the first one
> fixes this.
> 
> Without this, an "mjpeg_decode_dc: bad vlc: 0:0" error is thrown.
> 
> In all known files, the 2 codes are mapped to symbol 0 so only
> that case is checked.
> 
> [1]: Embedded JPEGs in "X7 RAW" and "X7 CinemaDNG" samples here:
>      https://www.dji.com/gr/zenmuse-x7/info#downloads
> 
> Signed-off-by: Nick Renieris <velocityra at gmail.com>
> ---
>  libavcodec/jpegtables.c | 17 ++++++++++++++---
>  libavcodec/tiff.c       |  6 +++---
>  2 files changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/libavcodec/jpegtables.c b/libavcodec/jpegtables.c
> index cbe5523cb4..fa5c6f9fc5 100644
> --- a/libavcodec/jpegtables.c
> +++ b/libavcodec/jpegtables.c
> @@ -130,14 +130,25 @@ void ff_mjpeg_build_huffman_codes(uint8_t *huff_size, uint16_t *huff_code,
>  {
>      int i, j, k,nb, code, sym;
>  
> -    code = 0;
> +    /* Some badly encoded files [1] map 2 different codes to symbol 0.
> +       Only the first one is valid, so we zero-initialize this here and
> +       make sure we only set it once (the first time) in the loop below.
> +
> +       [1]: Embedded JPEGs in "X7 RAW" and "X7 CinemaDNG" samples here:
> +            https://www.dji.com/gr/zenmuse-x7/info#downloads
> +     */
> +    huff_size[0] = 0;
> +
>      k = 0;
> +    code = 0;
>      for(i=1;i<=16;i++) {
>          nb = bits_table[i];
>          for(j=0;j<nb;j++) {
>              sym = val_table[k++];
> -            huff_size[sym] = i;
> -            huff_code[sym] = code;
> +            if (sym != 0 || huff_size[sym] == 0) { /* see comment above */
> +                huff_size[sym] = i;
> +                huff_code[sym] = code;
> +            }
>              code++;
>          }
>          code <<= 1;

> diff --git a/libavcodec/tiff.c b/libavcodec/tiff.c
> index dd1295fad6..78b4bd5301 100644
> --- a/libavcodec/tiff.c
> +++ b/libavcodec/tiff.c
> @@ -754,10 +754,10 @@ static int tiff_unpack_strip(TiffContext *s, AVFrame *p, uint8_t *dst, int strid
>  }
>  
>  static float av_always_inline linear_to_srgb(float value) {
> -    if (value <= 0.0031308)
> -        return value * 12.92;
> +    if (value <= 0.0031308f)
> +        return value * 12.92f;
>      else
> -        return pow(value * 1.055, 1.0 / 2.4) - 0.055;
> +        return powf(value * 1.055f, 1.0f / 2.4f) - 0.055f;
>  }

This looks unrelated


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Opposition brings concord. Out of discord comes the fairest harmony.
-- Heraclitus
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