On Wed, Oct 13, 2021 at 6:15 PM Mattias Wadman <mattias.wad...@gmail.com> wrote:
> Reduces the risk of finding false frames that happens to have valid values > and CRC. > > Fixes ticket #9185 ffmpeg flac decoder incorrectly finds junk frame > https://trac.ffmpeg.org/ticket/9185 > --- > libavcodec/flac_parser.c | 30 ++++++++++++++++++++++++++++-- > 1 file changed, 28 insertions(+), 2 deletions(-) > > diff --git a/libavcodec/flac_parser.c b/libavcodec/flac_parser.c > index d3d9c889a1..2c550507fc 100644 > --- a/libavcodec/flac_parser.c > +++ b/libavcodec/flac_parser.c > @@ -96,8 +96,34 @@ static int frame_header_is_valid(AVCodecContext *avctx, > const uint8_t *buf, > FLACFrameInfo *fi) > { > GetBitContext gb; > - init_get_bits(&gb, buf, MAX_FRAME_HEADER_SIZE * 8); > - return !ff_flac_decode_frame_header(avctx, &gb, fi, 127); > + uint8_t subframe_type; > + > + // header plus one byte from first subframe > + init_get_bits(&gb, buf, MAX_FRAME_HEADER_SIZE * 8 + 8); > + if (ff_flac_decode_frame_header(avctx, &gb, fi, 127)) { > + return 0; > + } > + // subframe zero bit > + if (get_bits1(&gb) != 0) { > + return 0; > + } > + // subframe type > + // 000000 : SUBFRAME_CONSTANT > + // 000001 : SUBFRAME_VERBATIM > + // 00001x : reserved > + // 0001xx : reserved > + // 001xxx : if(xxx <= 4) SUBFRAME_FIXED, xxx=order ; else reserved > + // 01xxxx : reserved > + // 1xxxxx : SUBFRAME_LPC, xxxxx=order-1 > + subframe_type = get_bits(&gb, 6); > + if (!(subframe_type == 0 || > + subframe_type == 1 || > + ((subframe_type >= 8) && (subframe_type <= 12)) || > + (subframe_type >= 32))) { > + return 0; > + } > + > + return 1; > } > > /** > -- > 2.29.2 > > Ping Maybe I should give some more context. I originally reported https://trac.ffmpeg.org/ticket/9185 after seeing decode errors 1-2 times a day in a system that decodes tens of thousands of FLAC files per day. All of the failing ones I've looked at decodes fine with the FLAC reference decoder and nearly all of them are encoded using "Switch Audio File Converter", but I've managed to make ffmpeg's FLAC encoder produce valid files that it fails on also. With the patch I haven't seen any errors for the last 2 weeks and I've also gone through older files and all have decoded fine. I've looked into solving this without adding more validation in the flac parser but failed. I can't see how to know the frame size without more or less decoding it. -Mattias _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
