Removing EIA-608 subtitles from mkv, FFMPEG filter_units unit docs

[nicholasserra]

Hey everyone, thanks for looking.

Trying to remove some EIA-608 subtitle streams from an mkv. MKVtoolnix won't remove them on multiplex.

I found a thread here:
https://forum.videohelp.com/threads/390217-Deleting-CEA-608-%28EIA-608%29-captions-fro...264-video-file

Where people are using FFMPEG to remove them with success. I tried with the example commands but no luck. I tried the "filter_units" bitstream filter with different unit numbers, and found that it WILL remove the streams, but I have no idea which unit number to be excluding. The above thread mentions unit number 6 for these subtitles, but that's not working for me.

Does anyone know if there's docs that simply have a list of bitstream unit type numbers? There seems to be hundreds, but I can't find any listing of them anywhere, even with ffmpeg's detailed docs.

Or if anyone else knows another trick to remove these, would be much appreciated. Thanks!

[sneaker]

Table 7-1 of the H.264 specs lists the nal_unit_types. But just like the thread you linked to says: SEIs are type 6.

Are you sure you are using ffmpeg correctly? Are you sure your subtitles are not e.g. hardcoded? Upload a sample and your complete ffmpeg log.

[nicholasserra]

Thank you!

I'm a bit confused on the unit_types stuff in general. This mkv has a mpeg2 video stream, so i'm guessing the h264 unit types don't apply? Not sure.

Here's a sample file:
https://nicholasserra-dropbox.s3.amazonaws.com/test.mkv

The subtitles aren't hardcoded, they show as separate streams. And they don't have any words, so i'm not sure what they actually are. Feels like just garbage from a standalone DVD transfer to me.

Hoping they aren't somehow baked into the mpeg2 stream?

[usually_quiet]

I examined your sample file, test.mkv, with VLC, MediaInfo, and eac3to to see if there were any closed captions available. None of them detected any closed captions, not even empty closed captions.

[Edit] The EIA 608 closed captions used for NTSC DVD and North American TV are stored in the video's GOP user data. At least one of these three programs should have detected that type of closed captioning if it was present.

[nicholasserra]

I'm seeing 4 streams of subtitles in VLC codec info. Check out the screenshot attached.

[poisondeathray]

You can use restream to remove user data from mpeg2 elementary streams

You would have to demux mpeg video elementary stream from mkv (you might have to rename extension for the video to .m2v in order for restream to "see" it )

[nicholasserra]

You can use restream to remove user data from mpeg2 elementary streams

You would have to demux mpeg video elementary stream from mkv (you might have to rename extension for the video to .m2v in order for restream to "see" it )

This did it! Thank you Guess the weird subtitles were embedded in the mpeg2 stream after all. The resulting file was only a couple hundred kilobytes smaller (3.44 gigs total) and no rerender done. Awesome

[usually_quiet]

The version of VLC which detected no closed captions was fairly old, although it could find and play CCs from my DVD and ATSC TV recordings. After I installed the latest version, VLC detected 4 closed caption streams.

The versions of MediaInfo, CCExtractor GUI, and eac3to that I tried were the latest and found nothing. I just tried the newest PotPlayer and it found no closed captions. VLC may or may not be correct.

[Edit]Never mind. I see that PDR found a solution.

[phelissimo_]

You can use restream to remove user data from mpeg2 elementary streams

You would have to demux mpeg video elementary stream from mkv (you might have to rename extension for the video to .m2v in order for restream to "see" it )

How do I remove the subtitles there? Can't find a option for it.

EDIT: nevermind

[cybergrimes]

You can use restream to remove user data from mpeg2 elementary streams

You would have to demux mpeg video elementary stream from mkv (you might have to rename extension for the video to .m2v in order for restream to "see" it )

This did it! Thank you Guess the weird subtitles were embedded in the mpeg2 stream after all. The resulting file was only a couple hundred kilobytes smaller (3.44 gigs total) and no rerender done. Awesome

Glad you posted this question here. Thanks @poisondeathray for the answer. I was trying an ffmpeg command from a different thread without any success. My file is from an older Blu-ray encoded with MPEG2. I used ReStream directly on the MKV, it completed but but the file had some issues. I got it working by using MKVCleaver to pull the video stream into an m2v file, then ran the m2v through ReStream and finally put it all back together with mkvmerge using the audio/chapters from the original MKV file.

fwiw, this file also would not report any closed caption data in MediaInfo. I was seeing the closed caption in Emby and VLC only, both reported as EIA-608. I noticed MediaInfo would report the EIA-608 text stream after the m2v was extracted from the MKV... *shrug*

[Ronstang]

It could be that you ran into a situation I ran into a while back. Some TV stations broadcast content with the four CC streams present but empty...thus they are just placeholders so some video players show they are there when you scan for info but will not display any CCs when you turn them on because they are not there....just the empty place holders. I drove myself crazy becaue my video player showed my TS files haveing 4 CC streams yet when I tried to extract them all I only got 1....because there was only one there.