CEA-708 is not supported at all for MP4 #52

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claunia · 2026-01-29T16:33:59Z

claunia commented

2026-01-29 16:33:59 +00:00

Originally created by @cfsmp3 on GitHub (Apr 17, 2015).

The MP4 code doesn't detect CEA-708, so obviously the decoder doesn't have a chance to process it.

I looked into this a bit and it might not be a lot of work.

We have one MP4 sample that contains 708 (only, no 608) in this directory:

/Chenders

From what I look, the track type is c708 which is correct (however the code in mp4.c skips it).
After that, comes the interesting thing. The atom type is not cdat (as the specs say should be for subtitles) but ccpd which is undocumented.

Someone in ffmpeg did some digging and explains here
https://trac.ffmpeg.org/ticket/3250

I think that should be enough to put us in the right direction.

Originally created by @cfsmp3 on GitHub (Apr 17, 2015). The MP4 code doesn't detect CEA-708, so obviously the decoder doesn't have a chance to process it. I looked into this a bit and it might not be a lot of work. We have one MP4 sample that contains 708 (only, no 608) in this directory: /Chenders From what I look, the track type is c708 which is correct (however the code in mp4.c skips it). After that, comes the interesting thing. The atom type is not cdat (as the specs say should be for subtitles) but ccpd which is undocumented. Someone in ffmpeg did some digging and explains here https://trac.ffmpeg.org/ticket/3250 I think that should be enough to put us in the right direction.

claunia closed this issue

2026-01-29 16:33:59 +00:00

claunia commented

2026-01-29 16:33:59 +00:00

@okisseloff commented on GitHub (Apr 24, 2015):

Spent some time trying to figure out why gpac mistakes calculating samples offsets :) (https://github.com/CCExtractor/ccextractor/pull/159)

Here comes my dev branch of mp4 CEA-708 support https://github.com/kisselef/ccextractor/tree/feature-mp4-c708-support. @cfsmp3 check it please to confirm that this is what you meant. If so, I'll run some more tests and will create a pull request.

@okisseloff commented on GitHub (Apr 24, 2015): Spent some time trying to figure out why gpac mistakes calculating samples offsets :) (https://github.com/CCExtractor/ccextractor/pull/159) Here comes my dev branch of mp4 CEA-708 support https://github.com/kisselef/ccextractor/tree/feature-mp4-c708-support. @cfsmp3 check it please to confirm that this is what you meant. If so, I'll run some more tests and will create a pull request.

claunia commented

2026-01-29 16:34:00 +00:00

@xvkdev commented on GitHub (Apr 24, 2015):

Haven't tested it but the changes seems reasonable.

About timing, I don't think the problem is with GPAC... we have the same problem with 708 inside MPEG-TS.

@xvkdev commented on GitHub (Apr 24, 2015): Haven't tested it but the changes seems reasonable. About timing, I don't think the problem is with GPAC... we have the same problem with 708 inside MPEG-TS.

claunia referenced this issue

2026-01-29 16:57:35 +00:00

[PR #52] compile and working on windows #949

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Reference: starred/ccextractor#52