Opened 18 years ago
Closed 18 years ago
#1558 closed patch (fixed)
Ignore timecode when decoding IVTV, EIA-608 Closed Captions
Reported by: | Owned by: | danielk | |
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Priority: | minor | Milestone: | 0.20 |
Component: | mythtv | Version: | head |
Severity: | medium | Keywords: | |
Cc: | Ticket locked: | no |
Description
This patch works around a couple of issues:
- Wrong timestamps used for IVTV CC. AVF "lastccptsu" is taken from video packets, which is appropriate for ATSC CC but not for IVTV VBI packets. This issue results in the problem reported by Robert Johnston here:
http://www.gossamer-threads.com/lists/mythtv/dev/184534#184534 (It is possible to fix this by using the pkt->pts from the VBI packets but that timestamp does not seem to be normalized.)
- ATSC CC timestamps not always in sequential order. Although AVF DecodeDTVCC now receives data in the correct order, the corresponding "lastccptsu" is not always incrementing. (There is probably a better way of calculating "lastccptsu".)
This patch allows the CC decoder to ignore the timecode. The main use of the timecode in the original (backend) V4L CC decoding was to detect false duplicate codes because VBI reads were not reliably synchronized to the frame rate. When decoding in the frontend, embedded VBI codes should be reliable. (The incorrect timecodes was defeating this duplicate detection, resulting in extra "erase" codes.)
Ignoring the timecode also disables logic which postpones "scroll-up" caption updates by accumulating characters in the same caption line. This was originally used to reduce the number of CC records when recording to NUV but this is not really an issue for AVF decoding. Also, disabling this logic for AVF allows "scroll-up" captions to be displayed more accurately (less "bursty"). However, the depth of NVP txtbuffers needed to be increased to handle the larger number of updates.
Some VERBOSE debugging has been added in CCDecoder.
NOTE: I do not have an IVTV card to test these changes but I have tested it on a sample IVTV stream provided by Robert.
Attachments (1)
Change History (4)
Changed 18 years ago by
Attachment: | ignore_cc_tc-9409.patch added |
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comment:1 Changed 18 years ago by
Sorry, the patch to ClassicCommDetector? was meant for Ticket #1557.
comment:2 Changed 18 years ago by
Milestone: | → 0.20 |
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Owner: | changed from Isaac Richards to danielk |
Status: | new → assigned |
Version: | → head |
comment:3 Changed 18 years ago by
Resolution: | → fixed |
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Status: | assigned → closed |
Ignore timecode in EIA-608 CC decoder