Hi, All.
I'm using libavcodec to decode APE files, and one of them starting like this:
4D 41 43 20 96 0F 00 00 34 00 00 00
( this file has been verified by mac )
and the function in libavcodec/apedec.c:
static av_cold int ape_decode_init(AVCodecContext * avctx)
{
// ...
s->avctx = avctx;
s->channels = avctx->channels;
s->fileversion = AV_RL16(avctx->extradata);
s->compression_level = AV_RL16(avctx->extradata + 2);
s->flags = AV_RL16(avctx->extradata + 4);
av_log(avctx, AV_LOG_DEBUG, "Compression Level: %d - Flags: %d\n",
s->compression_level, s->flags);
if (s->compression_level % 1000 || s->compression_level >
COMPRESSION_LEVEL_INSANE) {
av_log(avctx, AV_LOG_ERROR, "Incorrect compression level
%d\n", s->compression_level);
return -1;
}
s->fset = s->compression_level / 1000 - 1;
for (i = 0; i < APE_FILTER_LEVELS; i++) {
if (!ape_filter_orders[s->fset][i])
break;
s->filterbuf[i] = av_malloc((ape_filter_orders[s->fset][i] * 3
+ HISTORY_SIZE) * 4);
}
// ...
}
The file version( 96 0F ) is 3990, which is correct.
But the compression level( 00 00 ) is 0, so s->fset will be -1,
and ape_filter_orders[s->fset] will be ... ?
Notice that 0 can pass test
(s->compression_level % 1000 || s->compression_level >
COMPRESSION_LEVEL_INSANE),
but it is not regular compress level. ( Is it? )
I don't know why my program won't crash at run time,
but this compression level seems cause wrong offset
when decoding.
If 0 is not a regular value, should this codec guess a right value, or
just log an error?
Thanks.
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