Opened 13 years ago
Closed 13 years ago
#10273 closed Patch - Bug Fix (fixed)
CEA-708 captions are delayed because of incorrect byte-pair handling
| Reported by: | Owned by: | danielk | |
|---|---|---|---|
| Priority: | minor | Milestone: | 0.25 |
| Component: | MythTV - ATSC | Version: | Master Head |
| Severity: | medium | Keywords: | cea-708 |
| Cc: | Ticket locked: | no |
Description
ATSC closed captions (CEA-708) are sometimes delayed due do a bug in the way the DTVCC transport layer is packetized. According to the CEA-708 specification:
"The end of the packet is indicated by either: (1) receipt of the header (cc_valid = 1, cc_type = 11) of the next DTVCC packet, or (2) receipt of a byte-pair where cc_valid = 0 and cc_type = 10 or cc_type = 11."
But only case (1) is handled currently. As a result, a received packet will not be processed until the next one arrives, which in some cases only occurs after a long time has passed. This usually manifests in roll-up captions that are missing the last letter or two until more text appears, on in pop-on captions that appear too late, not leaving enough time for the viewer to read them before they disappear.
The attached patch adds handling for case (2). I have tested it with the PBS test material (http://ncamftp.wgbh.org/DTV/CEA%20test%20material/) and recorded programs from various local ATSC stations. The delays are gone, and I have not observed any new problems.
Attachments (1)
Change History (2)
Changed 13 years ago by
| Attachment: | cc708-null-fix.patch added |
|---|
comment:1 Changed 13 years ago by
| Milestone: | unknown → 0.25 |
|---|---|
| Resolution: | → fixed |
| Status: | new → closed |
CEA-708: Fix delayed presentation of some captions.
Patch from argilo@… (received with thanks) - see #10273 for details. Fixes a number of test streams with no obvious regressions.
Closes #10273
Branch: master Changeset: f8312c35f01980be8d10a048cc23220f11864211
fix for delayed closed captions