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[34.83.118.50]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-23de4359c68sm51340395ad.213.2025.07.11.14.29.11 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 11 Jul 2025 14:29:11 -0700 (PDT) From: Andreas Rheinhardt X-Google-Original-From: Andreas Rheinhardt Message-Id: <87b2a6bd77bb531ef0a1f703a4dc81dcead7ecd6.1752269335.git.ffmpegagent@gmail.com> In-Reply-To: References: X-Original-From: Andreas Rheinhardt Date: Fri, 11 Jul 2025 21:28:52 +0000 Fcc: Sent MIME-Version: 1.0 To: ffmpeg-devel@ffmpeg.org Subject: [FFmpeg-devel] [PATCH 2/4] avformat/oggdec: Don't skip over data whose checksum is used X-BeenThere: ffmpeg-devel@ffmpeg.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: FFmpeg development discussions and patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: FFmpeg development discussions and patches Cc: Andreas Rheinhardt Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Archived-At: List-Archive: List-Post: From: Andreas Rheinhardt The behavior of the ffio_*_checksum feature is not well defined when using avio_skip(). The code in oggdec.c relied on the skipped data (four bytes) to be checksummed, which is mostly true because short_seek_threshold is 32768 by default, so that avio_seek() will normally read data instead of calling the underlying seek function. Yet this has two problems: a) It relies on implementation details of avio_seek(). b) There is an exception, namely if the AVIO_FLAG_DIRECT is set. In this case the underlying seek function (if set) is always called and the data is skipped, leading to CRC errors. So don't skip the data. Signed-off-by: Andreas Rheinhardt --- libavformat/oggdec.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/libavformat/oggdec.c b/libavformat/oggdec.c index da3ef815db..9dc2c62035 100644 --- a/libavformat/oggdec.c +++ b/libavformat/oggdec.c @@ -370,7 +370,7 @@ static int ogg_read_page(AVFormatContext *s, int *sid, int probing) flags = avio_r8(bc); gp = avio_rl64(bc); serial = avio_rl32(bc); - avio_skip(bc, 4); /* seq */ + avio_rl32(bc); /* seq */ crc_tmp = ffio_get_checksum(bc); crc = avio_rb32(bc); -- ffmpeg-codebot _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".