Re: [FFmpeg-devel] [PATCH v7 0/4] add ARIB caption decoder using libaribcaption

[TADANO Tokumei <aimingoff@pc.nifty.jp>]

On 2023/02/28 9:07, Ridley Combs wrote:
> 
>> On Feb 23, 2023, at 04:17, TADANO Tokumei <aimingoff@pc.nifty.jp> wrote:
>>
>> Ping with rebased patch set.
>> Some chages are added to reflect review results from outside of this ML.
>>
>> ---
>> This patch set add another ARIB caption decoder using libaribcaption
>> external library: https://github.com/xqq/libaribcaption
>> The library decodes subtitles of ISDB-based TV broadcasting.
>> It is not only for Japanese ARIB STD-B24 caption, but also for
>> Brazilian ABNT NBR 15606-1 and Philippines version of ISDB-T.
>>
>> Unlike libaribb24, it supports 3 types of subtitle outputs:
>> * text: plain text
>> * ass: ASS formatted text
>> * bitmap: bitmap image
>>
>> Default subtitle type is ASS as same as libaribb24.
>> Advantages compared with libaribb24 on ASS subtitle are:
>> * Subtitle positioning.
>> * Multi-rect subtitle: some captions are displayed at different
>>   position at a time.
>> * More stability and reproducibility.
>>
>> Subtitle type can be changed by `-sub_type` option.
>> You can see ARIB caption with ffplay tool:
>>   ffplay -sub_type bitmap MPEG.TS
>>
>> Sample files exist under:
>>   https://streams.videolan.org/streams/ts/ARIB/
>> Some of them are encrypted and some don't contain ARIB caption data.
>> Good samples for ARIB caption are:
>>   brazil/07-25_20-33-35_UCV - HD_.ts
>>   japan/channel2[137]_clear.ts
>>   japan/osaka_15.ts
>>
>> ---
>> v7: reflect review results from outside of this ML
>>   - rename -ass_workaround option to -ass_single_rect and default to
>>     false (latest mpv supports multiple ASS rectangle)
>>   - add -canvas_size option to specify frame size to render bitmap subtitle
>>   - add -caption_encoding option to specify encoding of subtitle text
>>   - change behavior of profile C ARIB caption
>>   - some cosmetic changes
>> v6: reflect review results from outside of this ML
>>   - check clut table overflow
>>   - do not adjust vertical position of ruby for ASS format
>> v5: reflect review comments from Mao Hata
>>   - reset correct variable in aribcaption_close()
>>   - add aribcaption_close() to some places in aribcaption_init()
>>   - check if av_strdup() returns NULL in set_ass_header()
>> v4: reflect review results from outside of this ML.
>>   - resize bitmap subtitle image to display fonts with correct aspect ratio
>>   - multiple font families can be specified by '-font' option
>>   - remove 'rendering_backend' option
>>   - add document
>>   - minor bug fixes
>> v3: combine former 1/4 and 2/4 due to the patchwork shows build error.
>>   - fix help option content which incorrectly separated to 2 lines in 2/4.
>>   - amend commit message of 4/4.
>>
>> TADANO Tokumei (4):
>>   lavc/libaribcaption.c: add ARIB caption decoder using libaribcaption
>>   lavc/codec_desc.c: remove AV_CODEC_PROP_TEXT_SUB property
>>   lavf/mpegts.c: set some properties for ARIB caption
>>   doc/decoders.texi: add document of aribcaption decoder
>>
>> configure                   |    4 +
>> doc/decoders.texi           |  150 +++++
>> libavcodec/Makefile         |    1 +
>> libavcodec/allcodecs.c      |    1 +
>> libavcodec/codec_desc.c     |    1 -
>> libavcodec/libaribb24.c     |    1 +
>> libavcodec/libaribcaption.c | 1171 +++++++++++++++++++++++++++++++++++
>> libavformat/mpegts.c        |    6 +-
>> 8 files changed, 1333 insertions(+), 2 deletions(-)
>> create mode 100644 libavcodec/libaribcaption.c
>>
>> -- 
>> 2.30.2
>>
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> 
> This set looks reasonable to me at this point; the one thing blocking it is the issue with assenc.c muxing for AVSubtitles with multiple rects, which needs a decision on this question: http://ffmpeg.org/pipermail/ffmpeg-devel/2023-February/306850.html

I think this patch set can be applied independently from your patch.
If you want to export ARIB captions to ASS format, specifying
`-ass_single_rect true` is sufficient as a tentative solution.
Of course positioning information would be lost, but is valid ASS format.
Your patch has worth to improve the output, but it can be resolved later.
  
> Once that's resolved, I'm happy to merge this.
> 
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