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

[Michael Niedermayer]

On Sat, Apr 06, 2019 at 10:44:00AM +0200, Lynne wrote:
> Apr 4, 2019, 10:30 AM by michael at niedermayer.cc:
> 
> > On Wed, Mar 06, 2019 at 02:47:37PM +0100, Lynne wrote:
> >
> >> 6 Mar 2019, 11:22 by >> dev at lynne.ee <mailto:dev at lynne.ee>>> :
> >>
> >> > 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.
> >> >
> >> v2 attached
> >>
> >> apedec.c |   26 +++++++++++++++++++++++++-
> >>  1 file changed, 25 insertions(+), 1 deletion(-)
> >> c0cc550d77927ee0349094a4976f73d0ef671ff6  0001-apedec-add-ability-to-check-CRC-v2.patch
> >> From 68c25bb026761eacda3c276148e2beb34e8929fd Mon Sep 17 00:00:00 2001
> >> From: Lynne <>> dev at lynne.ee <mailto:dev at lynne.ee>>> >
> >> Date: Wed, 6 Mar 2019 11:01:01 +0000
> >> Subject: [PATCH v2] 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 | 26 +++++++++++++++++++++++++-
> >>  1 file changed, 25 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/libavcodec/apedec.c b/libavcodec/apedec.c
> >> index 15eb416ba4..a20d884606 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 = UINT32_MAX;
> >>  if ((ctx->fileversion > 3820) && (ctx->CRC & 0x80000000)) {
> >>  ctx->CRC &= ~0x80000000;
> >>  
> >> @@ -1548,6 +1551,27 @@ static int ape_decode_frame(AVCodecContext *avctx, void *data,
> >>  
> >>  s->samples -= blockstodecode;
> >>  
> >> +    if ((avctx->err_recognition & AV_EF_CRCCHECK) &&
> >>
> >> +        (s->fileversion >= 3900) && (s->bps < 24)) {
> >>
> >
> > what about file versions other than this ? do they have no crc ?
> >
> They have a different CRC version which is poorly documented.
> 
> 
> 

> >
> > what about othet bps ?
> >
> 24 bit CRC needs to ignore the zeroes padding each sample in 32 bits. I couldn't find any 24-bit files so I left that for a future patch.

can such a file not be generated ? or
maybe printing a note and asking for a sample in this case would be an option
if noone has one either ...

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
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