Currently, we have a AV_CODEC_ID_SSA, which matches the way the ASS/SSA
markup is muxed in a standalone .ass/.ssa file. This means the AVPacket
data starts with a "Dialogue:" string, followed by a timing information
(start and end of the event as string) and a trailing CRLF after each
line. One packet can contain several lines. We'll refer to this layout
as "SSA" or "SSA lines".
In matroska, this markup is not stored as such: it has no "Dialogue:"
prefix, it contains a ReadOrder field, the timing information is not in
the payload, and it doesn't contain the trailing CRLF. See [1] for more
info. We'll refer to this layout as "ASS".
Since we have only one common codec for both formats, the matroska
demuxer is constructing an AVPacket following the "SSA lines" format.
This causes several problems, so it was decided to change this into
clean ASS packets.
Some insight about what is changed or unchanged in this commit:
CODECS
------
- the decoding process still writes "SSA lines" markup inside the ass
fields of the subtitles rectangles (sub->rects[n]->ass), which is
still the current common way of representing decoded subtitles
markup. It is meant to change later.
- new ASS codec id: AV_CODEC_ID_ASS (which is different from the
legacy AV_CODEC_ID_SSA)
- lavc/assdec: the "ass" decoder is renamed into "ssa" (instead of
"ass") for consistency with the codec id and allows to add a real
ass decoder. This ass decoder receives clean ASS lines (so it starts
with a ReadOrder, is followed by the Layer, etc). We make sure this
is decoded properly in a new ass-line rectangle of the decoded
subtitles (the ssa decoder OTOH is doing a simple straightforward
copy). Using the packet timing instead of data string makes sure the
ass-line now contains the appropriate timing.
- lavc/assenc: just like the ass decoder, the "ssa" encoder is renamed
into "ssa" (instead of "ass") for consistency with the codec id, and
allows to add a real "ass" encoder.
One important thing about this encoder is that it only supports one
ass rectangle: we could have put several dialogue events in the
AVPacket (separated by a \0 for instance) but this would have cause
trouble for the muxer which needs not only the start time, but also
the duration: typically, you have merged events with the same start
time (stored in the AVPacket->pts) but a different duration. At the
moment, only the matroska do the merge with the SSA-line codec.
We will need to make sure all the decoders in the future can't add
more than one rectangle (and only one Dialogue line in it
obviously).
FORMATS
-------
- lavf/assenc: the .ass/.ssa muxer can take both SSA and ASS packets.
In the case of ASS packets as input, it adds the timing based on the
AVPacket pts and duration, and mux it with "Dialogue:", trailing
CRLF, etc.
- lavf/assdec: unchanged; it currently still only outputs SSA-lines
packets.
- lavf/mkv: the demuxer can now output ASS packets without the need of
any "SSA-lines" reconstruction hack. It will become the default at
next libavformat bump, and the SSA support will be dropped from the
demuxer. The muxer can take ASS packets since it's muxed normally,
and still supports the old SSA packets. All the SSA support and
hacks in Matroska code will be dropped at next lavf bump.
[1]: http://www.matroska.org/technical/specs/subtitles/ssa.html
This commit also makes sure the extradata and subtitle_header are NUL
terminated, without taking into account the trailing '\0' in account in
the size.
At the same time, it should fix 'warning: dereferencing type-punned
pointer will break strict-aliasing rules' warning for compilers who
don't consider uint8_t** and char** compatibles.
* commit '23aae62c2cb4504a09ceb8cd0cabc1c8b260f521':
alsdec: Check k used for rice decoder.
avfiltergraph: silence an uninitialized variable warning
xsubenc: reindent
lavc: replace AVCodecContext.encode with subtitle-specific callback
lavc: add const to private codec class initialization.
avconv: don't pass a bogus parameter to avfilter_graph_create_filter().
id3v2: strdup the genre name explicitly.
lavf/id3v2: do not export empty fields.
buffersrc: add const to the AVFrame* argument of av_buffersrc_write_frame()
lavfi: replace empty input/output lists with null pointers
Conflicts:
ffmpeg_filter.c
libavcodec/alsdec.c
libavcodec/dvdsubenc.c
libavcodec/utils.c
libavcodec/v210dec.h
libavfilter/af_channelsplit.c
libavfilter/avfiltergraph.c
libavfilter/buffersrc.c
libavfilter/src_movie.c
libavfilter/vf_ass.c
Merged-by: Michael Niedermayer <michaelni@gmx.at>
* qatar/master:
Fix even more missing includes after the common.h removal
build: Factor out rangecoder dependencies to CONFIG_RANGECODER
build: Factor out error resilience dependencies to CONFIG_ERROR_RESILIENCE
x86: avcodec: Consistently name all init files
Add more missing includes after removing the implicit common.h
Add some more missing includes after removing the implicit common.h
Don't include common.h from avutil.h
rtmp: Automatically compute the hash for SWFVerification
Conflicts:
configure
doc/APIchanges
doc/examples/decoding_encoding.c
libavcodec/Makefile
libavcodec/assdec.c
libavcodec/audio_frame_queue.c
libavcodec/avpacket.c
libavcodec/dv_profile.c
libavcodec/dwt.c
libavcodec/libtheoraenc.c
libavcodec/rawdec.c
libavcodec/rv40dsp.c
libavcodec/tiff.c
libavcodec/tiffenc.c
libavcodec/v210dec.h
libavcodec/vc1dsp.c
libavcodec/x86/Makefile
libavfilter/asrc_anullsrc.c
libavfilter/avfilter.c
libavfilter/buffer.c
libavfilter/formats.c
libavfilter/vf_ass.c
libavfilter/vf_drawtext.c
libavfilter/vf_fade.c
libavfilter/vf_select.c
libavfilter/video.c
libavfilter/vsrc_testsrc.c
libavformat/version.h
libavutil/audioconvert.c
libavutil/error.h
libavutil/version.h
Merged-by: Michael Niedermayer <michaelni@gmx.at>
* qatar/master:
mpc8: return more meaningful error codes.
mpc: return more meaningful error codes.
wv,mpc8: don't return apetag data in packets.
rtmp: do not warn about receiving metadata packets
x86: h264dsp: Adjust YASM #ifdefs
x86: yadif: Mark mmxext optimizations as such
h264: convert loop filter strength dsp function to yasm.
Improve descriptiveness of a number of codec and container long names
Conflicts:
libavcodec/flvdec.c
libavcodec/libopenjpegdec.c
libavformat/apetag.c
libavformat/mp3dec.c
Merged-by: Michael Niedermayer <michaelni@gmx.at>
None of these symbols should be accessed directly, so declare them as
hidden.
Signed-off-by: Mans Rullgard <mans@mansr.com>
(cherry picked from commit d36beb3f69)
Clément Bœsch