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

Lynne dev at lynne.ee
Tue Apr 9 16:56:09 EEST 2019




Apr 7, 2019, 12:56 AM by michael at niedermayer.cc:

> On Sat, Apr 06, 2019 at 10:44:00AM +0200, Lynne wrote:
>
>> Apr 4, 2019, 10:30 AM by >> michael at niedermayer.cc <mailto: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>>>  <mailto:>> 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>>>  <mailto:>> 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 ...
>

I think skipping the check for such files is okay for now. Its just for verification purposes after all, and not all decoders implement the option but silently skip it.


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