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new 5e95a3ddfb avcodec/dovi_rpudec: skip full padding byte if it is
already aligned
5e95a3ddfb is described below
commit 5e95a3ddfbdb68e81bbe58db10c75961566c7c02
Author: Kacper Michajłow <[email protected]>
AuthorDate: Wed Jun 3 17:42:24 2026 +0200
Commit: Kacper Michajłow <[email protected]>
CommitDate: Mon Sep 7 00:40:53 2026 +0000
avcodec/dovi_rpudec: skip full padding byte if it is already aligned
On some files when we land already at a byte boundary, there is a full
padding byte added by the encoder. Skip this byte and also validate
it's zero as the alignment padding should be.
It is likely just an encoder quirk that adds padding always, and if it
is aligned, it does full additional byte.
When extremely unlikely situation happens that we cannot infer
terminator position by looking at the surrounding bytes, calculate crc
twice, to avoid failing it on padded streams.
Signed-off-by: Kacper Michajłow <[email protected]>
---
libavcodec/dovi_rpudec.c | 23 ++++++++++++++++++++++-
1 file changed, 22 insertions(+), 1 deletion(-)
diff --git a/libavcodec/dovi_rpudec.c b/libavcodec/dovi_rpudec.c
index ba4e7cd214..d0374f6717 100644
--- a/libavcodec/dovi_rpudec.c
+++ b/libavcodec/dovi_rpudec.c
@@ -721,18 +721,39 @@ int ff_dovi_rpu_parse(DOVIContext *s, const uint8_t *rpu,
size_t rpu_size,
av_refstruct_unref(&s->ext_blocks);
}
+ int aligned = get_bits_count(gb) % 8 == 0;
align_get_bits(gb);
+
+ /* The payload is followed by a CRC32 and a 0x80 terminator. Some encoders
+ * emit an extra zero padding byte before the CRC32 when the payload
already
+ * ended on a byte boundary. A leading zero byte is then ambiguous: it may
+ * be that padding, or simply a CRC32 that starts with a zero byte. If only
+ * the padded position holds the terminator, assume the padding is real. If
+ * both do (the last CRC32 byte is 0x80 or there is stray 0x80 after real
+ * payload) the terminator position is ambiguous. Calculate CRC twice when
+ * AV_EF_CRCCHECK is requested. Note that this situation is extremely
+ * unlikely, there shouldn't be non-zero data after payload. */
+ int pad = aligned && show_bits(gb, 8) == 0;
skip_bits(gb, 32); /* CRC32 */
- if (get_bits(gb, 8) != 0x80) {
+ int term_unpadded = get_bits(gb, 8) == 0x80; /* terminator w/o
padding */
+ int term_padded = pad && show_bits(gb, 8) == 0x80; /* terminator w/
padding */
+
+ if (!term_unpadded && !term_padded) {
avpriv_request_sample(s->logctx, "Unexpected RPU format");
ff_dovi_ctx_unref(s);
return AVERROR_PATCHWELCOME;
}
if (err_recognition & AV_EF_CRCCHECK) {
+ if (term_padded && !term_unpadded)
+ skip_bits(gb, 8); /* unambiguously padded */
rpu_size = get_bits_count(gb) / 8;
uint32_t crc = av_bswap32(av_crc(av_crc_get_table(AV_CRC_32_IEEE),
-1, rpu, rpu_size - 1)); /* exclude 0x80 */
+ if (crc && term_padded && term_unpadded) {
+ crc = av_bswap32(av_crc(av_crc_get_table(AV_CRC_32_IEEE),
+ -1, rpu, rpu_size)); /* include padding
byte */
+ }
if (crc) {
av_log(s->logctx, AV_LOG_ERROR, "RPU CRC mismatch: %X\n", crc);
if (err_recognition & AV_EF_EXPLODE) {
--
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