- From: Bob Lund <B.Lund@CableLabs.com>
- Date: Fri, 26 Sep 2014 22:12:01 +0000
- To: Jon Piesing <Jon.Piesing@tpvision.com>, Silvia Pfeiffer <silviapfeiffer1@gmail.com>, "alexander.adolf@condition-alpha.com" <alexander.adolf@condition-alpha.com>
- CC: "public-inbandtracks@w3.org" <public-inbandtracks@w3.org>, Nigel Megitt <nigel.megitt@bbc.co.uk>
- Message-ID: <D049F21F.464E3%b.lund@cablelabs.com>
Hi Alexander, I’ve provided comments below for the diffs in the MPEG-2 TS section. I will provide more comments for the DASH and ISOBMFF section diffs. Regards, Bob On 9/24/14, 6:51 AM, "Jon Piesing" <Jon.Piesing@tpvision.com<mailto:Jon.Piesing@tpvision.com>> wrote: Sylvia, In particular, I would like to know if we really need to distinguish three different types of MPEG-2 TS formats?? Well if a UA interprets a DVB TS according to the rules for an ASTC TS it's going to give wrong results. >From a quick look at the differences between the two sets of text, the ATSC rules would not recognise any DVB subtitle (+caption) tracks and would not recognise some DVB video and audio tracks. <snip> Also: what's the purpose in not exposing any of the cue content for MPEG-2 TS ? HbbTV has no requirement for this and it seems like a lot of work. DVB has many, many different ways of carrying data in an MPEG-2 transport stream and there's no outright winner or lowest common denominator. Jon ________________________________________ From: Silvia Pfeiffer [silviapfeiffer1@gmail.com<mailto:silviapfeiffer1@gmail.com>] Sent: 22 September 2014 11:52 To: alexander.adolf@condition-alpha.com<mailto:alexander.adolf@condition-alpha.com> Cc: public-inbandtracks@w3.org<mailto:public-inbandtracks@w3.org>; Jon Piesing; Nigel Megitt Subject: Re: Proposal from HbbTV For those looking for a quick summary of the changes, the best way to look at Alexander's changes is by diff. I've also extracted Alexander's change notes so you can give feedback right here on this thread. In particular, I would like to know if we really need to distinguish three different types of MPEG-2 TS formats?? And if so, does anyone have the missing information on ISDB? Also, I would suggest creating a completely separate section for these different formats since they are so fundamentally different from each other. Also: what's the purpose in not exposing any of the cue content for MPEG-2 TS ? 1) Diff for the MPEG-DASH section: ============================ http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-dash%2Findex.html Change notes and rationale: * We are proposing to source DASH EventStreams as text tracks. These are e.g. used for ad insertion, and for dealing with timelines in second screen applications. * The updates to the table for sourcing the attributes of text tracks other than event streams try to provide further detail and align with MPEG-DASH and DVB's profile of it. * The updates to the table for sourcing the attributes of audio and video tracks try to provide further detail and align with MPEG-DASH and DVB's profile of it. * At the end of the section, we propose a new table for sourcing the attributes of text tracks representing DASH EventStreams. 2) Diff for MPEG-4 ISO-BMFF section: ============================== http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-isobmff%2Findex.html Change notes and rationale: We are proposing adding support for W3C TTML 2nd edition, and for EBU-TT-D as captions and subtitles. The note below the table tries to give some guidance on the various profiles and extensions that both SMPTE-TT and EBU-TT-D apply to TTML. The value of the 'namespace' field in the 'XMLSubtitleSampleEntry' is still under discussion. unfortunately, the ISOBMFF spec remains sufficiently vague ("...shall be set to indicate the namespace...") to warrant further discussion. Concatenating the namespaces in angle brackets to make the string discernable to URI parser is one option. Another option would be to use short names as hinted in the ISOBMFF spec (e.g. "TTML+SMPTETT"). But then there is no registry yet to provide the mappings and help avoid name clashes. 3. Changes for MPEG-2 TS section: ============================ 1. http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-1%2Findex.html The added text for determining the type of broadcast system does not appear to be something the UA needs to do. AFAICT in the diffs below, all DVB cases reference DVB specific information or descriptors for doing some DVB specific action. Theses won’t exist in the ATSC case. And, the ATSC specific information won’t exist in DVB. So, the UA can just do the ATSC action or DVB action based on the presence of ATSC or DVB information. 2. http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-2%2Findex.html There doesn’t appear to be a need to the UA to distinguish based on broadcast system so no need to change the first paragraph. The table based on broadcast system type doesn’t add any value. Audio, video and text tracks are identified in DVB just as in ATSC – based on stream_type and the presence of specific descriptors. You should keep the text format that is there and add to it. For example, in text tracks: text track: * The elementary stream with PID 0x02 or the stream type value is "0x02", "0x05", "0x80", between "0x82" and "0x86", or between "0x88 and 0xFF". * The CEA 708 caption service [CEA708 <#bib-CEA708>], as identified by a 'Caption Service Descriptor' [ATSC65 <#bib-ATSC65>] in the 'Elementary Stream Descriptors' in the PMT entry for a video stream with stream type 0x02 or 0x1B. * a DVB subtitle component [DVB-SUB <http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-2%2Findex.html#bib-DVB-SUB>] as identified by a 'subtitling_descriptor' [DVB-SI <http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-2%2Findex.html#bib-DVB-SI>] in the 'Elementary Stream Descriptors' in the PMT entry for a stream with a 'stream_type' of "0x06" Do the same for audio and video tracks. 3. http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-3%2Findex.html Keep the existing table format For @id, why doesn’t the use of PID work. And, why can’t the pid be a decimal representation as in the case of ATSC? For @kind, keep the same format as is currently used, just add new bullets for the DVB case, e.g. * "captions”: * for a caption service * for a DVB subtitle component [DVB-SUB<http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-3%2Findex.html#bib-DVB-SUB>] as identified by a 'subtitling_descriptor' [DVB-SI<http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-3%2Findex.html#bib-DVB-SI>] in the PMT with a 'subtitling_type' in the range "0x20" to "0x25" * an ITU-R System B Teletext component [DVB-TXT<http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-3%2Findex.html#bib-DVB-TXT>] as identified by an 'teletext_descriptor' [DVB-SI<http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-3%2Findex.html#bib-DVB-SI>] with a 'teletext_type' value of "0x05" in the PMT * a VBI data component [DVB-VBI<http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-3%2Findex.html#bib-DVB-VBI>] as identified by a 'VBI_teletext_descriptor' [DVB-SI<http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-3%2Findex.html#bib-DVB-SI>] with a 'teletext_type' value of "0x05" in the PMT * "subtitles”: * if the stream type value is “0x82" * for a DVB subtitle component [DVB-SUB<http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-3%2Findex.html#bib-DVB-SUB>] as identified by a 'subtitling_descriptor' [DVB-SI<http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-3%2Findex.html#bib-DVB-SI>] in the PMT with a 'subtitling_type' in the range "0x10" to "0x15" * an ITU-R System B Teletext component [DVB-TXT<http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-3%2Findex.html#bib-DVB-TXT>] as identified by an 'teletext_descriptor' [DVB-SI<http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-3%2Findex.html#bib-DVB-SI>] with a 'teletext_type' value of "0x02" in the PMT * a VBI data component [DVB-VBI<http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-3%2Findex.html#bib-DVB-VBI>] as identified by a 'VBI_teletext_descriptor' [DVB-SI<http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-3%2Findex.html#bib-DVB-SI>] with a 'teletext_type' value of "0x02" in the PMT * "metadata": otherwise Same for @language and @label 4. http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-4%2Findex.html Same comments as for #3 above: why can’t PID be used for track ID, add DVB cases in existing section format. 5. http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-5%2Findex.html (note: this patch destroys the document structure) There doesn’t seem to be a need to describe a case that is not used If there are no elementary streams of the type identified as a metatdata text track then no cues will be created. 6. http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-6%2Findex.html (note: this patch destroys the document structure) I don’t understand this. First, you state generically that caption cues are exposed as DataCue. This is may not be true for ATSC. Then you define a DVB DataCue that doesn’t have any fields populated, except pause_on_exit. I suggest the following instead: MPEG-2 TS captions are in the CEA 708 format [CEA708]. Caption data is are carried in the video stream in Picture User Data [ATSC53-4] for 'stream_type' 0x02 and in Supplemental Enhancement Information [ATSC72-1] for 'stream_type' 0x1B. Browsers that can render the CEA 708 format should expose them in as yet to be specified CEA708Cue objects. Alternatively, browsers can also map the CEA 708 features to WebVTTCue objects [VTT708]. Finally, browsers that cannot render CEA 708 captions should expose them as DataCue objects [HTML5]. In this case, each 'service block' in a digital TV closed caption (DTVCC) transport channel creates a DataCue object with TextTrackCue attributes sourced as follows: Table as it currently exists. Since there is no definition of any other MPEG-2 TS caption cue than 708 there seems to be no reason to say that an undefined thing is not exposed. 7. http://services.w3.org/htmldiff?doc1=https%3A%2F%2Frawgit.com%2Fsilviapfeiffer%2FHTMLSourcingInbandTracks%2Fmaster%2Findex.html&doc2=https%3A%2F%2Frawgit.com%2Fc-alpha%2FHTMLSourcingInbandTracks%2Fhbbtv-mpeg2ts-7%2Findex.html (note: this patch destroys the document structure) Same comments as captions. Change existing text to: MPEG-2 subtitles are in the SCTE 27 format [SCTE27]. Browsers that can render the SCTE 27 format should be exposed them in as yet to be specified SCTE27Cue objects. Alternatively, browsers can also map the SCTE 27 features to WebVTTCue object via an as yet to be specified mapping process. Finally, browsers that cannot render SCTE 27 subtitles, should expose them as DataCue objects [HTML5]. In this case, each 'section' in an elementary stream identified as a subtitles text track creates a DataCue object with TextTrackCue attributes sourced as follows: Leave the table as is. Statement about DVB subtitles not being exposed seems unnecessary since there is no definition of how to do it. Change notes and rationale summary: The text you currently have deals with ATSC systems only. We propose to add support for DVB and ISDB systems, too. In the proposed updates to the opening of the MPEG2-TS section, we set the scene for TS originating from different kinds of broadcast systems. The link to "ATSC Worldwide" is a dead one as I couldn't find any such page. This may seem logical for a national SDO at first, but then ATSC is used in South Korea and in most countries in South America; whence creating an "ATSC Worldwide" page might actually make sense. Regards, Silvia. On Mon, Sep 22, 2014 at 6:24 PM, Silvia Pfeiffer <silviapfeiffer1@gmail.com<mailto:silviapfeiffer1@gmail.com>> wrote: On Wed, Sep 17, 2014 at 8:29 AM, <alexander.adolf@condition-alpha.com<mailto:alexander.adolf@condition-alpha.com>> wrote: Dear Media Resource In-band Tracks Community Group, As suggested by Silvia and Bob, I have refactored the pull request on GitHub into smaller chunks, which hopefully will be easier to handle. The comments on GitHub to each of them contains a link to a visual diff. They can all be merged without conflicts. If you go through them one by one and merge them all, the end result will be identical to what the initial, big pull request contains. Please ignore all the commits in the GitHub history, and focus on the diffs (visual or source, whichever works better for you). ---------------------------------------------------------------------- https://github.com/silviapfeiffer/HTMLSourcingInbandTracks/pull/2 This contains the changes to the MPEG DASH section. ---------------------------------------------------------------------- https://github.com/silviapfeiffer/HTMLSourcingInbandTracks/pull/3 This contains the changes to the ISOBMFF section. ---------------------------------------------------------------------- https://github.com/silviapfeiffer/HTMLSourcingInbandTracks/pull/4 https://github.com/silviapfeiffer/HTMLSourcingInbandTracks/pull/5 https://github.com/silviapfeiffer/HTMLSourcingInbandTracks/pull/6 https://github.com/silviapfeiffer/HTMLSourcingInbandTracks/pull/7 https://github.com/silviapfeiffer/HTMLSourcingInbandTracks/pull/8 https://github.com/silviapfeiffer/HTMLSourcingInbandTracks/pull/9 https://github.com/silviapfeiffer/HTMLSourcingInbandTracks/pull/10 These contain the changes to the MPEG2-TS part, on a section by section basis. ---------------------------------------------------------------------- Please see the GitHub comments for each of the pull requests for more details. I have however not included the references in these pull requests to improve the signal to noise ratio. I will of course add the references to https://github.com/tobie/specref as you approve and merge the pull requests. I hope that this refactoring is along the lines of what you had expected. Many thanks and cheers, --alexander adolf Hi Alexander, Thanks for grouping the patches logically. You have, however, somehow made them on my fork of the spec rather than on the w3c's main spec in GitHub: https://github.com/w3c/HTMLSourcingInbandTracks I will review them on my fork, but it will make sense for you to change your upstream to be the one of w3c. Also, Bob is our main expert around MPEG, so he will probably be the one to merge your patches. Regards, Silvia.
Received on Friday, 26 September 2014 22:12:40 UTC