- From: Dirk-Willem van Gulik <Dirk-Willem.van.Gulik@BBC.co.uk>
- Date: Wed, 12 Jan 2011 00:23:59 +0000
Right - but that foregoes a bit how subtle the SMPTE timecode definition is (http://en.wikipedia.org/wiki/SMPTE_time_code is a good start) - and this is exactly why it is defined in such odd a manner (as you do have exactly this tautology problem between, say, NTSC and PAL). So yes - you want do express this - knowing full well that once you have less than one frame/second the interpretation is a bit odd. But ultimately it does let you define exactly where a cut/splice/etc is - and how exactly two things are overlaid, etc. Dw. On 11 Jan 2011, at 22:51, David Singer wrote: > OK, but it does seem kinda a tautology if you say "I want to use a time-expression that represents fractions of seconds as frame numbers, and it's not very accurate if there aren't very many frames/second..." ! > > On Jan 11, 2011, at 23:40 , Rob Coenen wrote: > >> Hi David- that is b/c in an ideal world I'd want to seek to a time expressed as a SMPTE timecode (think web apps that let users step x frames back, seek y frames forward etc.). In order to convert SMPTE to the floating point value for video.seekTime I need to know the frame rate. >> >> -Rob >> >> On Tue, Jan 11, 2011 at 10:35 PM, David Singer <singer at apple.com> wrote: >> 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. >> >> > > David Singer > Multimedia and Software Standards, Apple Inc. >
Received on Tuesday, 11 January 2011 16:23:59 UTC