Currently, AVStream contains an embedded AVCodecContext instance, which
is used by demuxers to export stream parameters to the caller and by
muxers to receive stream parameters from the caller. It is also used
internally as the codec context that is passed to parsers.
In addition, it is also widely used by the callers as the decoding (when
demuxer) or encoding (when muxing) context, though this has been
officially discouraged since Libav 11.
There are multiple important problems with this approach:
- the fields in AVCodecContext are in general one of
* stream parameters
* codec options
* codec state
However, it's not clear which ones are which. It is consequently
unclear which fields are a demuxer allowed to set or a muxer allowed to
read. This leads to erratic behaviour depending on whether decoding or
encoding is being performed or not (and whether it uses the AVStream
embedded codec context).
- various synchronization issues arising from the fact that the same
context is used by several different APIs (muxers/demuxers,
parsers, bitstream filters and encoders/decoders) simultaneously, with
there being no clear rules for who can modify what and the different
processes being typically delayed with respect to each other.
- avformat_find_stream_info() making it necessary to support opening
and closing a single codec context multiple times, thus
complicating the semantics of freeing various allocated objects in the
codec context.
Those problems are resolved by replacing the AVStream embedded codec
context with a newly added AVCodecParameters instance, which stores only
the stream parameters exported by the demuxers or read by the muxers.
Fixes use of uninitialized memory
Fixes: signal_sigsegv_504fb0_10_signal_sigsegv_504fb0_343_mewmew_ssa.avi
Found-by: Mateusz j00ru Jurczyk and Gynvael Coldwind
After this the order from the original file is stored through readorder
when doing ffmpeg -i input.ass -c copy output.mkv.
And now that the ASS muxer honors the ReadOrder, extracting the ass back
(without transcoding) restores the original order.
Use the UTF-16 BOM to detect UTF-16 encoding. Convert the file contents
to UTF-8 on the fly using FFTextReader, which acts as converting wrapper
around AVIOContext. It also can work on a static buffer, needed for
format probing. The FFTextReader wrapper now also takes care of skipping
the UTF-8 BOM.
Fix Ticket #3496.
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.
This also lists the objects from those two libraries as internal (by adding
the ff_ prefix) so that they can then be hidden via linker scripts.
(cherry picked from commit c6610a216e)