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avcodec/flac_parser: Fix off-by-one error

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The flac parser uses a fifo to buffer its data. Consequently, when
searching for sync codes of flac packets, one needs to take care of
the possibility of wraparound. This is done by using an optimized start
code search that works on each of the continuous buffers separately and
by explicitly checking whether the last pre-wrap byte and the first
post-wrap byte constitute a valid sync code.

Moreover, the last MAX_FRAME_HEADER_SIZE - 1 bytes ought not to be searched
for (the start of) a sync code because a header that might be found in this
region might not be completely available. These bytes ought to be searched
lateron when more data is available or when flushing.

Unfortunately there was an off-by-one error in the calculation of the
length to search of the post-wrap buffer: It was too large, because the
calculation was based on the amount of bytes available in the fifo from
the last pre-wrap byte onwards. This meant that a header might be
parsed twice (once prematurely and once regularly when more data is
available); it could also mean that an invalid header will be treated as
valid (namely if the length of said invalid header is
MAX_FRAME_HEADER_SIZE and the invalid byte that will be treated as the
last byte of this potential header happens to be the right CRC-8).

Should a header be parsed twice, the second instance will be the best child
of the first instance; the first instance's score will be
FLAC_HEADER_BASE_SCORE - FLAC_HEADER_CHANGED_PENALTY ( = 3) higher than
the second instance's score. So the frame belonging to the first
instance will be output and it will be done as a zero length frame (the
difference of the header's offset and the child's offset). This has
serious consequences when flushing, as returning a zero length buffer
signals to the caller that no more data will be output; consequently the
last frames not yet output will be dropped.

Furthermore, a "sample/frame number mismatch in adjacent frames" warning
got output when returning the zero-length frame belonging to the first
header, because the child's sample/frame number of course didn't match
the expected sample frame/number given its parent.

filter/hdcd-mix.flac from the FATE-suite was affected by this (the last
frame was omitted) which is the reason why several FATE-tests needed to
be updated.

Fixes ticket #5937.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
This commit is contained in:
Andreas Rheinhardt 2019-10-06 07:01:15 +02:00 committed by Paul B Mahol
parent d03c3e8517
commit e5e5be4c7f
2 changed files with 10 additions and 10 deletions
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4
libavcodec/flac_parser.c
View File

@ -244,9 +244,9 @@ static int find_new_headers(FLACParseContext *fpc, int search_start)
uint8_t wrap[2];
wrap[0] = buf[read_len - 1];
read_len = search_end - search_start + 1;
/* search_start + 1 is the post-wrap offset in the fifo. */
read_len = search_end - (search_start + 1) + 1;
buf = flac_fifo_read(fpc, search_start + 1, &read_len);
wrap[1] = buf[0];

16
tests/fate/filter-audio.mak
View File

@ -312,47 +312,47 @@ FATE_AFILTER_SAMPLES-$(call FILTERDEMDECENCMUX, HDCD, FLAC, FLAC, PCM_S24LE, PCM
fate-filter-hdcd-mix: SRC = $(TARGET_SAMPLES)/filter/hdcd-mix.flac
fate-filter-hdcd-mix: CMD = md5 -i $(SRC) -af hdcd -f s24le
fate-filter-hdcd-mix: CMP = oneline
fate-filter-hdcd-mix: REF = e7079913e90c124460cdbc712df5b84c
fate-filter-hdcd-mix: REF = 77443573e0bd3532de52a8bc0e825da7
# output will be different because of the gain mismatch in the second and third parts
FATE_AFILTER_SAMPLES-$(call FILTERDEMDECENCMUX, HDCD, FLAC, FLAC, PCM_S24LE, PCM_S24LE) += fate-filter-hdcd-mix-psoff
fate-filter-hdcd-mix-psoff: SRC = $(TARGET_SAMPLES)/filter/hdcd-mix.flac
fate-filter-hdcd-mix-psoff: CMD = md5 -i $(SRC) -af hdcd=process_stereo=false -f s24le
fate-filter-hdcd-mix-psoff: CMP = oneline
fate-filter-hdcd-mix-psoff: REF = bd0e81fe17696b825ee3515ab928e6bb
fate-filter-hdcd-mix-psoff: REF = 89e57885917a436b30855db4d478cefb
# test the different analyze modes
FATE_AFILTER_SAMPLES-$(call FILTERDEMDECENCMUX, HDCD, FLAC, FLAC, PCM_S24LE, PCM_S24LE) += fate-filter-hdcd-analyze-pe
fate-filter-hdcd-analyze-pe: SRC = $(TARGET_SAMPLES)/filter/hdcd-mix.flac
fate-filter-hdcd-analyze-pe: CMD = md5 -i $(SRC) -af hdcd=analyze_mode=pe -f s24le
fate-filter-hdcd-analyze-pe: CMP = oneline
fate-filter-hdcd-analyze-pe: REF = bb83e97bbd0064b9b1c0ef2f2c8f0c77
fate-filter-hdcd-analyze-pe: REF = 2d839d8a1cf73b10a566ce3d4cfaa79e
FATE_AFILTER_SAMPLES-$(call FILTERDEMDECENCMUX, HDCD, FLAC, FLAC, PCM_S24LE, PCM_S24LE) += fate-filter-hdcd-analyze-lle
fate-filter-hdcd-analyze-lle: SRC = $(TARGET_SAMPLES)/filter/hdcd-mix.flac
fate-filter-hdcd-analyze-lle: CMD = md5 -i $(SRC) -af hdcd=analyze_mode=lle -f s24le
fate-filter-hdcd-analyze-lle: CMP = oneline
fate-filter-hdcd-analyze-lle: REF = 121cc4a681aa0caef5c664fece7a3ddc
fate-filter-hdcd-analyze-lle: REF = b4b185332b7025c191062f49a2c015f1
FATE_AFILTER_SAMPLES-$(call FILTERDEMDECENCMUX, HDCD, FLAC, FLAC, PCM_S24LE, PCM_S24LE) += fate-filter-hdcd-analyze-cdt
fate-filter-hdcd-analyze-cdt: SRC = $(TARGET_SAMPLES)/filter/hdcd-mix.flac
fate-filter-hdcd-analyze-cdt: CMD = md5 -i $(SRC) -af hdcd=analyze_mode=cdt -f s24le
fate-filter-hdcd-analyze-cdt: CMP = oneline
fate-filter-hdcd-analyze-cdt: REF = 12136e6a00dd532994f6edcc347af1d4
fate-filter-hdcd-analyze-cdt: REF = afa6577675c63e87da3edbd442b7b6e2
FATE_AFILTER_SAMPLES-$(call FILTERDEMDECENCMUX, HDCD, FLAC, FLAC, PCM_S24LE, PCM_S24LE) += fate-filter-hdcd-analyze-tgm
fate-filter-hdcd-analyze-tgm: SRC = $(TARGET_SAMPLES)/filter/hdcd-mix.flac
fate-filter-hdcd-analyze-tgm: CMD = md5 -i $(SRC) -af hdcd=analyze_mode=tgm -f s24le
fate-filter-hdcd-analyze-tgm: CMP = oneline
fate-filter-hdcd-analyze-tgm: REF = a3c39f62e9b9b42c9c440d0045d5fb2f
fate-filter-hdcd-analyze-tgm: REF = 285f0fd2249b4903cd5e1ad5ce004219
# the two additional analyze modes from libhdcd
FATE_AFILTER_SAMPLES-$(call FILTERDEMDECENCMUX, HDCD, FLAC, FLAC, PCM_S24LE, PCM_S24LE) += fate-filter-hdcd-analyze-ltgm
fate-filter-hdcd-analyze-ltgm: SRC = $(TARGET_SAMPLES)/filter/hdcd-mix.flac
fate-filter-hdcd-analyze-ltgm: CMD = md5 -i $(SRC) -af hdcd=analyze_mode=lle:process_stereo=false -f s24le
fate-filter-hdcd-analyze-ltgm: CMP = oneline
fate-filter-hdcd-analyze-ltgm: REF = 76ffd86b762b5a93332039f27e4c0c0e
fate-filter-hdcd-analyze-ltgm: REF = 404dc2301ea97e9f96c3d6d2ebcfeaa5
FATE_AFILTER_SAMPLES-$(call FILTERDEMDECENCMUX, HDCD, FLAC, FLAC, PCM_S24LE, PCM_S24LE) += fate-filter-hdcd-analyze-pel
fate-filter-hdcd-analyze-pel: SRC = $(TARGET_SAMPLES)/filter/hdcd-mix.flac
fate-filter-hdcd-analyze-pel: CMD = md5 -i $(SRC) -af hdcd=analyze_mode=pe:force_pe=true -f s24le
fate-filter-hdcd-analyze-pel: CMP = oneline
fate-filter-hdcd-analyze-pel: REF = 8156c5a3658d789ab46447d62151f5e9
fate-filter-hdcd-analyze-pel: REF = 9342983208ec1a7f2b3e332ac4dcb723
FATE_AFILTER_SAMPLES-$(call FILTERDEMDECENCMUX, HDCD, FLAC, FLAC, PCM_S24LE, PCM_S24LE) += fate-filter-hdcd-false-positive
fate-filter-hdcd-false-positive: SRC = $(TARGET_SAMPLES)/filter/hdcd-false-positive.flac