Livestream: Playback with Closed Caption

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floh79

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Livestream: Playback with Closed Caption

PostMon Oct 11, 2021 12:28 pm

Hi, I need a solution to deliver stream from existing videofiles like MP4 with SRT-file to CDN. So we have a streaming with closed caption. Which BMD device offer this feature :?: The new HyperDeck Studio XYZ and ATEM mini XYZ?

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Floh
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floh79

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Re: Livestream: Playback with Closed Caption

PostWed Oct 13, 2021 10:34 am

Hi I found out the BMD Web Presenter 4K supports closed caption:
Closed Captions
Web Presenter 4K supports embedding CEA‑608 and CEA‑708 closed captions in your live RTMP stream.


So I still don't know how to embed. Do I still need a CC-Encoder which sends the SDI-signal with the CC embedded to the Web Presenter 4K, or is there a way for the Web Presenter 4K to encode CC itself? Or I just need to embed the subtitle with Davinci Resolve (see screenshot) and then play with Hyperdeck Studio XYZ?

Bildschirmfoto 2021-10-13 um 12.31.40.png
Bildschirmfoto 2021-10-13 um 12.31.40.png (50.28 KiB) Viewed 589 times


Suggestions are warmly welcomed. ;) I just don't have the devices (Hyperdeck Studio, Web Presenter, ...) so I cannot just try out. :( I have to be 100% sure before I order these devices.

Best regards
Floh
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Edgriswold

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Re: Livestream: Playback with Closed Caption

PostWed Oct 13, 2021 4:22 pm

Are you wanting to caption a live stream or a post production ?
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Dave Del Vecchio

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Re: Livestream: Playback with Closed Caption

PostWed Oct 13, 2021 7:16 pm

For the Web Presenter HD or 4K, the captions need to be embedded in the SDI ancillary data of the SDI video input in either CEA‑608 or CEA‑708 format. If they are present in the SDI ancillary data, the Web Presenter will detect and indicate this on the monitoring screen and the captions will be included in the RTMP output: https://www.blackmagicdesign.com/produc ... monitoring

There isn't any kind of other mechanism in the Web Presenter at the moment to embed captions from some other external source.

In terms of closed captioning on the HyperDecks, I believe they record captions embedded in the SDI video input as a sidecar file in the MacCaption VANC format (.mcc files):
https://www.prweb.com/releases/2013/4/prweb10609376.htm

Given the way playback works for other formats on the HyperDeck, I would presume that if you were able to generate a video file and corresponding .mcc caption file in exactly the same format as one of the HyperDeck's built-in recording formats, then it would playout the video with the captions as ancillary data in the SDI output.

Regarding how to generate such a file from Resolve, I am not sure. I'm pretty sure that Premiere supports the .mcc format, but there was an earlier discussion thread in the DaVinci Resolve section of the forum about various difficulties with caption output from Resolve, and I'm not sure whether this is still the case:
viewtopic.php?f=32&t=95822

Also note that the specs page for the current HyperDeck models only mentions support for CEA‑708 captions and not the earlier analog-era CEA-608 format: https://www.blackmagicdesign.com/produc ... s/W-HYD-14
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rogersuski

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Re: Livestream: Playback with Closed Caption

PostWed Oct 13, 2021 8:07 pm

I can perform a test in the next few days whether the mcc files are accessed upon playback and then those contents placed in the anc portion of the video data. I'm dubious, however a press release I have stumbled across says it should work. Challenge will be providing the proper format of the mcc file to marry with the video. And making a video file that will play back without incident from the hyperdeck. Alternatively, you could great prores files with the data in the anc and then the webpresenter should handle the playback just like any other video source and encode the anc caption data into the h264 stream.
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floh79

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Re: Livestream: Playback with Closed Caption

PostThu Oct 14, 2021 6:55 am

Hello everybody,

@Edgriswold: Like the title says I want to caption a live stream by play back premade (=postproduction ;) ) videos.

The Idea about MacCaption sounds good, but the software itself is expensive... :/ I'm working mostly for small non-profits organizations. (FYI: I'm deaf and I'm working for accessibility-project like producing sign language videos and producing/applying subtitles for videos and accessible video streams.)

Yes I earlier found the thread and it's sad that someone has to use Premiere Pro instead of DaVinci Resolve and it's still the case since the last post is June 2021, tested with Davinci Resolve version 17. :(

It's fine by me with CEA-708 which is the prefered one.

@rogersuski: That would be great! Thank you for willing to test it. ProRes should be fine for me, any format are fine as long as DaVinci Resolve support this one.

I want to clarify: How many subtitle language can I use with CEA-708? Only one? Multiple so viewer can select the desired subtitle language? (that is for me the main reason for closed caption)

Best regards
Floh
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Dave Del Vecchio

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Re: Livestream: Playback with Closed Caption

PostFri Oct 15, 2021 4:33 am

floh79 wrote:I want to clarify: How many subtitle language can I use with CEA-708? Only one? Multiple so viewer can select the desired subtitle language? (that is for me the main reason for closed caption)
CEA-708 allows for up to 63 caption service channels which can support different languages. This is up from 4 caption channels that were supported in CEA-608.

Now, whether or not you can generate multiple caption streams from Premiere, Resolve, or another NLE, I am not sure. And even if multiple caption service streams were included with a broadcast, whether the receiving end would process and allow access to all of them, I am also not about. This may depend on various parts broadcast path.

In the ATSC broadcast specifications, for example, there is some mention of a limit of 16 caption service descriptors, so in practice you may be limited to less than 63 allowed in CEA-708. And it wouldn't surprise me if some receivers only provide access to a single caption channel.

And I'd imagine that for internet broadcasts, things are probably even less standardized. YouTube for example, supports CEA-608/CEA-708 embedded captions for live streams, but only uses the first caption track if there is more than one: https://support.google.com/youtube/answer/3068031
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floh79

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Re: Livestream: Playback with Closed Caption

PostFri Oct 15, 2021 10:26 pm

Hello, thank you very much for your detailed explaination. So I have to find out how multi language subtitle works with our CDN-Provider. I'll wait for the test result of rogersuski before I decide to buy devices for further testing.

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Floh
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Rey Kroona

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Re: Livestream: Playback with Closed Caption

PostSun Oct 17, 2021 4:48 pm

Hi,
I've done some closed captioning things in the past so I know how confusing this all can be, especially in a livestream environment. Blackmagic can also be mysteriously vague on more complex things like this, so I feel that pain.

I'm sure you've thought through this, but does it absolutely have to be a livestream? If you can live with an on-demand scenario. For example, uploading to Vimeo then sending the video to Rev.com and be translated to your various languages would be much simpler than trying to livestream with multiple languages.

If you really need livestream maybe look into some "simulated live" setups. I've seen this where it forces the YouTube or Vimeo player to be in sync with a time. So it feels like a live video, everyone is watching it at the same time, but it's on a true livestream.

One other thought, I know you used to be able to add closed captions in QuickTime 7 Pro pretty easily. I think it was just a copy & paste situation. I don't know if you can still get QuickTime 7 Pro or if it even runs on current OS's, but might be worth checking out if Premiere doesn't work out (I think I read premiere only supports 608 in a QuickTime file, otherwise you have to use MXF Op1a, but I'm not sure if the Hyperdeck will playback those files.

Anyways, good luck, I'm interested to hear how this gets going.

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