Subtitle Filtering 2022
===
This is a substantial update to the earlier subtitle filtering patch series.
A primary goal has been to address others' concerns as much as possible on
one side and to provide more clarity and control over the way things are
working. Clarity is is specifically important to allow for a better
understanding of the need for a subtitle start pts value that can be
different from the frame's pts value. This is done by refactoring the
subtitle timing fields in AVFrame, adding a frame field to indicate repeated
subtitle frames, and finally the full removal of the heartbeat
functionality, replaced by a new 'subfeed' filter that provides different
modes for arbitrating subtitle frames in a filter graph. Finally, each
subtitle filter's documentation has been amended by a section describing the
filter's timeline behavior (in v3 update).
Subtitle Filtering Demos
I published a demonstration of subtitle filtering capabilities with OCR,
text and bitmap subtitle manipulation involved: Demo 1: Text-Manipulation
with Bitmap Subtitles
[https://github.com/softworkz/SubtitleFilteringDemos/tree/master/Demo1]
v9
==
* Cleared the cc recipient list
* Resending after e-mail error
v8
==
* Rebased and adapted to upstream changes
v7
==
* Revert loglevel change
* snull: propagate format
* fftools/ffmpeg: ensure monotonic (frame-)pts values for subtitles
v6 - Fix assertion errors
=
* text2graphicsub: fix null point on uninit after error
* strim: propagate width and height
* avfilter: add default propagation time_base from inlink to outlink
v5 - Conversion to Graphic Subtitles, and other enhancements
* I'm glad to announce that Traian (@tcoza) has joined the project and
contributed a new 'text2graphicsub' filter to convert text subtitles to
graphic subtitles, which can in turn be encoded as dvd, dvb or x-subs
(and any other encoder for graphic subs that might be added in the
future). This filter closes the last open "gap" in subtitle processing.
* stripstyles filter: now allows very fine-grained control over which ASS
style codes should be preserved or stripped
* stripstyles: do not drop dialog margin values
* subfeed filter: eliminates duplicate frames with duplicate start times
when 'fix_overlap' is specified
* textmod: do not drop effect values
* graphicsub2text: reduce font size jitter
* ass_split: add function to selectively preserve elements when splitting
* add strim, snull and ssink and further unify subtitle frame handling with
audio and video
* ffmpeg_filter: get simple filter notation working for subtitles
v4 - Quality Improvements
=
* finally an updated version
* includes many improvements from internal testing
* all FATE tests passed
* all example commands from the docs verified to work
* can't list all the detail changes..
* I have left out the extra commits which can be handled separately, just
in case somebody wonders why these are missing:
* avcodec/webvttenc: Don't encode drawing codes and empty lines
* avcodec/webvttenc: convert hard-space tags to
* avutil/ass_split: Add parsing of hard-space tags (\h)
* avutil/ass_split: Treat all content in curly braces as hidden
* avutil/ass_split: Fix ass parsing of style codes with comments
v3 - Rebase
===
due to merge conflicts - apologies.
Changes in v2
=
* added .gitattributes file to enforce binary diffs for the test refs that
cannot be applied when being sent via e-mail
* perform filter graph re-init due to subtitle "frame size" change only
when the size was unknown before and not set via -canvas_size
* overlaytextsubs: Make sure to request frames on the subtitle input
* avfilter/splitcc: Start parsing cc data on key frames only
* avcodec/webvttenc: Don't encode ass drawing codes and empty lines
* stripstyles: fix mem leak
* gs2t: improve color detection
* gs2t: empty frames must not be skipped
* subfeed: fix name
* textmod: preserve margins
* added .gitattributes file to enforce binary diffs for the test refs that
cannot be applied when being sent via e-mail
* perform filter graph re-init due to subtitle "frame size" change only
when the size was unknown before and not set via -canvas_size
* avcodec/dvbsubdec: Fix conditions for fallback to default resolution
* Made changes suggested by Andreas
* Fixed failing command line reported by Michael
Changes from previous version v24:
AVFrame
===
* Removed sub_start_time The start time is now added to the subtitle
start_pts during decoding The sub_end_time field is adjusted accordingly
* Renamed sub_end_time to duration which it is effectively after removing
the start_time
* Added a sub-struct 'subtitle_timing' to av frame Contains subtitle_pts
renamed to 'subtitle_timing.start_pts' and
