lavf: replace AVStream.codec with AVStream.codecpar

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.

1 files changed, 4 insertions, 4 deletions

diff --git a/libavformat/rtp.h b/libavformat/rtp.h
index feaf167965..01b83dfa23 100644
--- a/libavformat/rtp.h
+++ b/libavformat/rtp.h
@@ -32,11 +32,11 @@
  * The format context private option payload_type overrides both.
  *
  * @param fmt   The context of the format
- * @param codec The context of the codec
+ * @param par   The codec parameters
  * @param idx   The stream index
  * @return The payload type (the 'PT' field in the RTP header).
  */
-int ff_rtp_get_payload_type(AVFormatContext *fmt, AVCodecContext *codec,
+int ff_rtp_get_payload_type(AVFormatContext *fmt, AVCodecParameters *par,
                             int idx);
 
 /**
@@ -46,12 +46,12 @@ int ff_rtp_get_payload_type(AVFormatContext *fmt, AVCodecContext *codec,
  * information depending on the payload type; for audio codecs, the
  * channels and sample_rate fields are also filled.
  *
- * @param codec The context of the codec
+ * @param par The codec parameters
  * @param payload_type The payload type (the 'PT' field in the RTP header)
  * @return In case of unknown payload type or dynamic payload type, a
  * negative value is returned; otherwise, 0 is returned
  */
-int ff_rtp_get_codec_info(AVCodecContext *codec, int payload_type);
+int ff_rtp_get_codec_info(AVCodecParameters *par, int payload_type);
 
 /**
  * Return the encoding name (as defined in