RE: tvapi-ACTION-24: use of Media Capture to realize recording requirements

Thank you Paul for the taking the action.

I created a dedicated wiki page to measure the progress of the spec [1], and captured Paul's analysis in the progress measurement wiki. Note that this progress measurement wiki is liked from the "API Specification" section in our main wiki page [2].

Thanks
Bin

[1] https://www.w3.org/community/tvapi/wiki/Main_Page/Progress_Measurement
[2] https://www.w3.org/community/tvapi/wiki/Main_Page#API_Specification

From: Paul Higgs [mailto:paul.higgs@ericsson.com]
Sent: Thursday, February 19, 2015 2:34 PM
To: public-tvapi@w3.org
Subject: RE: tvapi-ACTION-24: use of Media Capture to realize recording requirements

Following the "chain-of-specifications" a little further, it seems that the File API [5] specification can only construct a file from a single Blob (the blob is the output from the MediaStream Recording API).
It would be beneficial for our purposes if the File API included an "append( blob )" methods, then the first blob received from the recording could be used to create the file which subsequent blobs could be appended to.

It would probably be unrealistic to expect an single in-memory blob to contain an HD recording of an hour or more (given that would be 4+ GB of HD content)

Paul

[5] http://www.w3.org/TR/2013/WD-FileAPI-20130912/

From: Paul Higgs [mailto:paul.higgs@ericsson.com]
Sent: Thursday, February 19, 2015 3:38 PM
To: public-tvapi@w3.org<mailto:public-tvapi@w3.org>
Subject: tvapi-ACTION-24: use of Media Capture to realize recording requirements

Hi

During the February 17 TV Control API conference call, I took an action [1] to review the MediaStream Recording API [2] for its relevance and use in fulfilling the requirements around recording [3]

It is possible to see that an TVTuner defined in the TV Control API can "output" via a MediaStream which can then me recorded through the MediaRecorder API. In order to do this, the MediaRecorder constructor requires the mime type of the TVTuner output, so a "readonly attribute DOMString  mimeType" attribute should be added to the TVTuner interface.

At a period denoted by the timeSlice property, the ondataavailable event handler is trigger, an argument to which is the recorded data. The application implementing this handler would then need to write the capture stream data to a file (perhaps via the File API [4]). The MediaStream Recording API also has the ability to throw a "MediaRecorderErrorEvent" with name=OutOfMemory

What this means is that there is no native recording functionality in the device implementing TVManager.  Instead one of the applications running on the terminal is the "recording scheduler" (how that application gets and manages data is probably application specific). Note that this requires the UA support some form of "background application".

In essence, the requirement mapping table should, for each of the [recording.*] requirements, state "not supported, realized through the webapp and MediaStream Recording API"


[1] http://www.w3.org/community/tvapi/track/actions/24
[2] http://www.w3.org/TR/mediastream-recording/
[3] https://www.w3.org/community/tvapi/wiki/Main_Page/Technical_Requirement#Program_Recording_Requirements
[4] http://www.w3.org/TR/FileAPI/


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