W3C home > Mailing lists > Public > public-texttracks@w3.org > September 2012

RE: iOS6 WebVTT TextTrack Support in Safari

From: Goldstein, Glenn <glenn.goldstein@viacom.com>
Date: Wed, 26 Sep 2012 23:40:19 +0000
To: Eric Carlson <eric.carlson@apple.com>, John Foliot <john@foliot.ca>
CC: "public-texttracks@w3.org" <public-texttracks@w3.org>
Message-ID: <75386C677798CF40BE98B873913D0052147ED5@ABFABNJ04A.mtvn.ad.viacom.com>
i find this news about iOS6 on iPhone terribly disappointing. our workflow here for internet video is oriented around out-of-band captioning for on-demand content. we start with SCC files (608 captions) and can convert them to whatever format we need for use with specific players (SMPTE-TT, webVTT, etc...)

and we've been doing just fine with ActionScript and JavaScript renderers of SMPTE-TT. the problem is for our HTML5 player in safari on iPhone, our javascript code cannot render in video overlay. it was my hope that the solution would be the HTML5 video tag, with caption rendering managed by the user agent/native player.

reworking our encoding process to place captions in-band in h.264 video or in mp4 container is not realistic for us for several reasons. one issue, in particular, is the fact that we do some video in non 29.97 frame rates, creating challenges in injecting captions properly. our lowest bitrate mobile video is at 15fps, making in-band captions very challenging (608 captions are 2 bytes/frame).

HTML5 track seems like the elegant approach. ideally, it would support webVTT, SMPTE-TT, and SCC files (enabling perfect replication of TV 608 captions).


From: Eric Carlson [eric.carlson@apple.com]
Sent: Wednesday, September 26, 2012 5:59 PM
To: John Foliot
Cc: Goldstein, Glenn; public-texttracks@w3.org
Subject: Re: iOS6 WebVTT TextTrack Support in Safari

Hi John -

On Sep 26, 2012, at 2:47 PM, John Foliot <john@foliot.ca> wrote:

> Eric Carlson wrote:
>>  The lack of WebVTT support in MobileSafari on iOS 6 has nothing to do
>> with any of this, we just didn't have enough time to implement it.
> Thanks, so I guess I was misinformed: I thought that previously the videos
> were handed directly to the native media player on the handsets, and not
> rendered in the MobileSafari interface (was this ever the case, and has this
> changed, or have I just been clued out? Both possibilities exist)

  <video> in MobileSafari on the iPhone does always play in fullscreen, but not in another app. The experience is similar to playing fullscreen video on the desktop.

>>  In-band captions, eg. captions in an MPEG-4 container, have been
>> supported on iOS for some time.
> Yep, I should have been more precise, as this was what I was alluding to
> when I said "burned in". I know that initially that required the SCC caption
> file with Final Cut Pro, but am also aware that other, lighter-weight tools
> have emerged that allow for inclusion of caption files in the .mp4
> container.

  I assumed that you mean that captions had been pre-rendered into a video track when you said "burned-in". While authors can choose to do this, typically captions are added as a separate track which is then rendered as the video plays.

  I believe that Final Cut does allow an author to add captions to a video file, but quite a number of other tools - from various companies - do as well.

Received on Wednesday, 26 September 2012 23:57:26 UTC

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