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[82.13.65.128]) by smtp.gmail.com with ESMTPSA id n8-20020a5d67c8000000b00332e84210c2sm9832199wrw.88.2023.11.27.05.08.24 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Nov 2023 05:08:24 -0800 (PST) Message-ID: Date: Mon, 27 Nov 2023 13:08:43 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Content-Language: en-US To: ffmpeg-devel@ffmpeg.org References: <259cfc93-3e34-4081-8640-82890edbf76a@jkqxz.net> <20231025205553.GG3543730@pb2> From: Mark Thompson In-Reply-To: <20231025205553.GG3543730@pb2> Subject: Re: [FFmpeg-devel] [PATCH] cbs_av1: Reject thirty-two zero bits in uvlc code 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 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Archived-At: List-Archive: List-Post: On 25/10/2023 21:55, Michael Niedermayer wrote: > On Sun, Oct 22, 2023 at 07:35:52PM +0100, Mark Thompson wrote: >> The spec allows at least thirty-two zero bits followed by a one to mean >> 2^32-1, with no constraint on the number of zeroes. The libaom >> reference decoder does not match this, instead reading thirty-two zeroes >> but not the following one to mean 2^32-1. These two interpretations are >> incompatible and other implementations may follow one or the other. >> Therefore reject thirty-two zeroes because the intended behaviour is not >> clear. >> --- >> libaom, dav1d and SVT-AV1 all have the same nonstandard behaviour of stopping at thirty-two zeroes and not reading the one. gav1 just rejects thirty-two zeroes. > > I would suggest to contact the authors of the spec to bring this discrepancy > to their attention, unless this is already known and > unless this sequence is declared invalid by some other part of the spec > (which would make the discrepancy only occur in invalid sequences) Since this only occurs in nonconforming streams, fixing the spec seems like the better option. Thanks, - Mark _______________________________________________ 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".