1. 07 Jan, 2020 1 commit
    • Marton Balint's avatar
      avformat: remove avio_flush() calls from the end of write_header functions · 4bf90e09
      Marton Balint authored
      To make it consistent with other muxers.
      
      The user can still control the generic flushing behaviour after write_header
      (same way as after packets) using the -flush_packets option, the default
      typically means to flush unless a non-streamed file output is used.
      
      Therefore this change should have no adverse effect on streaming, even if it is
      assumed that the first packet has a clean buffer, so small seekbacks within the
      output buffer work even when the IO context is not seekable.
      Signed-off-by: 's avatarMarton Balint <cus@passwd.hu>
      4bf90e09
  2. 17 Aug, 2019 1 commit
  3. 26 Feb, 2016 2 commits
  4. 23 Feb, 2016 1 commit
    • Anton Khirnov's avatar
      lavf: replace AVStream.codec with AVStream.codecpar · 9200514a
      Anton Khirnov authored
      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.
      9200514a
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  16. 18 Apr, 2013 1 commit
    • Clément Bœsch's avatar
      subtitles: introduce ASS codec id and use it. · 7c1a002c
      Clément Bœsch authored
      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
      7c1a002c
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