- From: David Singer <singer@apple.com>
- Date: Tue, 11 Jan 2011 23:35:41 +0100
why does the frame rate make any difference on the accuracy of seeking to a time? Imagine a video that runs at 1 frame every 10 seconds, and I seek to 25 seconds. I would expect to see 5 seconds of the third frame, 10 seconds of the 4th, and so on. On Jan 11, 2011, at 18:54 , Rob Coenen wrote: > just a follow up question in relation to SMPTE / frame accurate playback: As > far as I can tell there is nothing specified in the HTML5 specs that will > allow us to determine the actual frame rate (FPS) of a movie? In order to do > proper time-code calculations it's essential to know both the video.duration > and video.fps - and all I can find in the specs is video.duration, nothing > in video.fps > > -Rob > > > On Mon, Jan 10, 2011 at 9:32 PM, Kevin Marks <kevinmarks at gmail.com> wrote: > >> If you really want to test timecode, you need to get into SMPTE drop-frame >> timecode too (possibly the single most annoying standards decision of. all >> time was choosing 30000/1001 as the framerate of NTSC video) >> >> Eric, can you make BipBop movie for this? - Like the ones used in this >> demo: >> >> >> http://developer.apple.com/library/mac/#documentation/NetworkingInternet/Conceptual/StreamingMediaGuide/UsingHTTPLiveStreaming/UsingHTTPLiveStreaming.html >> >> http://devimages.apple.com/iphone/samples/bipbopgear3.html >> >> >> On Mon, Jan 10, 2011 at 11:18 AM, Rob Coenen <coenen.rob at gmail.com> wrote: >> >>> Thanks for the update. >>> I have been testing with WebKit nightly / 75294 on MacOSX 10.6.6 / 13" >>> Macbook Pro, Core Duo. >>> >>> Here's a test movie that I created a while back. Nevermind the video >>> quality- the burned-in timecodes are 100% correct, I have verified this by >>> exploring each single frame by hand. >>> >>> >>> http://www.massive-interactive.nl/html5_video/transcoded_03_30_TC_sec_ReviewTest.mp4 >>> >>> Please let me know once you guys have downloaded the file, I like to >>> remove >>> it from my el-cheapo hosting account ASAP. >>> >>> thanks, >>> >>> Rob >>> >>> >>> On Mon, Jan 10, 2011 at 2:54 PM, Eric Carlson <eric.carlson at apple.com >>>> wrote: >>> >>>> >>>> On Jan 9, 2011, at 11:14 AM, Rob Coenen wrote: >>>> >>>> I have written a simple test using a H264 video with burned-in timecode >>>> (every frame is visually marked with the actual SMPTE timecode) >>>> Webkit is unable to seek to the correct timecode using 'currentTime', >>> it's >>>> always a whole bunch of frames off from the requested position. I reckon >>> it >>>> simply seeks to the nearest keyframe? >>>> >>>> WebKit's HTMLMediaElement implementation uses different media engines >>> on >>>> different platforms (eg. QuickTime, QTKit, GStreamer, etc). Each media >>>> engine has somewhat different playback characteristics so it is >>> impossible >>>> to say what you are experiencing without more information. Please file a >>> bug >>>> report at https://bugs.webkit.org/ with your test page and video file, >>> and >>>> someone will look into it. >>>> >>>> eric >>>> >>>> >>> >> >> David Singer Multimedia and Software Standards, Apple Inc.
Received on Tuesday, 11 January 2011 14:35:41 UTC