The high level summary of RCWT can be delegated doc/muxers, which
makes it easier to maintain and more consistent with the documentation
of the demuxer.
Signed-off-by: Marth64 <marth64@proxyid.net>
AVOutputFormat has default codecs for audio, video and subtitle
and often these are the only codecs of this type allowed.
So add a flag to AVOutputFormat so that this can be checked generically.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
More exactly: Not more than one stream of each type for which
a default codec (i.e. AVOutputFormat.(audio|video|subtitle)_codec)
is set; for those types for which no such codec is set (or for
which no designated default codec in AVOutputFormat exists at all)
no streams are permitted.
Given that with this flag set the default codecs become more important,
they are now set explicitly to AV_CODEC_ID_NONE for "unset";
the earlier code relied on AV_CODEC_ID_NONE being equal to zero,
so that default static initialization set it accordingly;
but this is not how one is supposed to use an enum.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
The formal title of the muxer according to the specification
is "RCWT (Raw Captions With Time)", so canonize this
in the long name of the codec and docs.
In the documentation section, point #2 was wrong: ccextractor
extracts the Closed Captions data and stores normalized bits
similarly to this muxer.
Signed-off-by: Marth64 <marth64@proxyid.net>
It does not use the AVFormatContext at all.
Reviewed-by: Marth64 <marth64@proxyid.net>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Resetting the counter of used elements is enough as nothing is
ever read from the currently unused elements.
Reviewed-by: Marth64 <marth64@proxyid.net>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
The rcwt muxer uses several counters for how much data
it has already cached: One byte counter and one counter
for how many complete blocks (of three bytes each).
These counters can become inconsistent when the muxer is
fed incomplete blocks as the muxer presumes that it is
about to write a new block at the start of each write_packet
call. E.g. sending 65535*3+1 1-byte packets (with data[0] e.g. 0x03)
will trigger an out-of-bounds write.
This patch fixes this by processing the data in complete blocks
only. This also allows to simplify the code, e.g. to remove one of
the counters.
Reviewed-by: Marth64 <marth64@proxyid.net>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Signed-off-by: Marth64 <marth64@proxyid.net>
Raw Captions With Time (RCWT) is a format native to ccextractor, a commonly
used open source tool for processing 608/708 closed caption (CC) sources.
It can be used to archive the original, raw CC bitstream and to produce
a source file file for later CC processing or conversion. As a result,
it also allows for interopability with ccextractor for processing CC data
extracted via ffmpeg. The format is simple to parse and can be used
to retain all lines and variants of CC.
A free specification of RCWT can be found here:
https://github.com/CCExtractor/ccextractor/blob/master/docs/BINARY_FILE_FORMAT.TXT
This muxer implements the specification as of 01/05/2024, which has
been stable and unchanged for 10 years as of this writing.
This muxer will have some nuances from the way that ccextractor muxes RCWT.
No compatibility issues when processing the output with ccextractor
have been observed as a result of this so far, but mileage may vary
and outputs will not be a bit-exact match.
Specifically, the differences are:
(1) This muxer will identify as "FF" as the writing program identifier, so
as to be honest about the output's origin.
(2) ffmpeg's MPEG-1/2, H264, HEVC, etc. decoders extract closed captioning
data differently than ccextractor from embedded SEI/user data.
For example, DVD captioning bytes will be translated to ATSC A53 format.
This allows ffmpeg to handle 608/708 in a consistant way downstream.
This is a lossless conversion and the meaningful data is retained.
(3) This muxer will not alter the extracted data except to remove invalid
packets in between valid CC blocks. On the other hand, ccextractor
will by default remove mid-stream padding, and add padding at the end
of the stream (in order to convey the end time of the source video).
