From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ffbox0-bg.mplayerhq.hu (ffbox0-bg.ffmpeg.org [79.124.17.100]) by master.gitmailbox.com (Postfix) with ESMTP id 7549640EA4 for ; Sat, 1 Jan 2022 00:42:06 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id 5072E68B072; Sat, 1 Jan 2022 02:42:04 +0200 (EET) Received: from mail.personalprojects.net (mail.personalprojects.net [51.79.67.80]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id 95EFC68B004 for ; Sat, 1 Jan 2022 02:41:58 +0200 (EET) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=personalprojects.net; s=20211201; h=Content-Transfer-Encoding:Content-Type: In-Reply-To:From:References:To:Subject:MIME-Version:Date:Message-ID:Sender: Reply-To:Cc:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=hVZJCEHuAfT+CVTTyIstArDapuuB52CEZfhj2GLbPyQ=; b=C+YImwPWw7LKwcsEVxvRbhqZoM Btsf4qpFeHKHfI7iv6QRB8b6wD6hAagwk8bZeGVXW7btQCRjOC+7+qEkL5CaTUqwqNiVFAwwaGpdJ 9Gt0llZw/td5ND6lkTeQ6QcJBSG3GzI4o3uISoiezMyasJiDqnqHp/r+eB+YkK52N1YU=; Received: from bras-base-simcon3012w-grc-05-64-231-188-105.dsl.bell.ca ([64.231.188.105] helo=[192.168.10.2]) by mail.personalprojects.net with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1n3ST7-0006j8-G8 for ffmpeg-devel@ffmpeg.org; Fri, 31 Dec 2021 19:41:57 -0500 Message-ID: Date: Fri, 31 Dec 2021 19:41:56 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.1 Content-Language: en-CA To: ffmpeg-devel@ffmpeg.org References: <20211231195019.16191-1-jpstewart@personalprojects.net> <80d511a7-846b-6803-171e-98e07eccb227@personalprojects.net> From: John-Paul Stewart In-Reply-To: Subject: Re: [FFmpeg-devel] [PATCH 0/2] avformat/mvdec: make audio stream conditional 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-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: On 2021-12-31 19:33, Andreas Rheinhardt wrote: > John-Paul Stewart: >> On 2021-12-31 17:19, Andreas Rheinhardt wrote: >>> John-Paul Stewart: >>>> Recent discussion on the list led me to realize that libavformat was >>>> unconditionally creating an audio stream for all SGI movie format >>>> (version 2) files, even when no audio is present in the file. >>>> >>>> A sample of a movie file with no audio can be found at >>>> http://www.personalprojects.net/ffmpeg/silent.movie >>>> >>>> Unpatched ffmpeg will report an audio stream even though no audio is >>>> present. After the following patch no audio stream is reported. >>>> >>>> SGI movie files with audio are slightly affected by the fact that the >>>> audio stream is now allocated after the video stream, changing the order >>>> they are listed in the output of ffprobe or ffmpeg. I don't think this >>>> materially affects anything. All existing FATE tests pass. >>>> >>> >>> If I am not mistaken, it actually changes it a bit more: The audio data >>> (if present) is stored before the video data in the file and >>> mv_read_packet returns the data in the order of the stream numbers. Now >> >> Thanks for that info. I hadn't realized that mv_read_packet relied on >> the order of the stream numbers. >> > > It is actually documented (right before creating the audio stream): > "/* allocate audio track first to prevent unnecessary seeking > * (audio packet always precede video packet for a given frame) */" I saw that, but thought it referred only to seeking through the metadata in the file header. I didn't realize that the comment meant the seeks would happen later in processing the actual data stream in another function. I didn't look at the code in enough detail to fully understand the comment. _______________________________________________ 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".