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, 17 insertions, 16 deletions

diff --git a/libavformat/gif.c b/libavformat/gif.c
index ddec778d82..e7fa37cfc7 100644
--- a/libavformat/gif.c
+++ b/libavformat/gif.c
@@ -264,7 +264,7 @@ static int gif_write_header(AVFormatContext *s)
 {
     GIFContext *gif = s->priv_data;
     AVIOContext *pb = s->pb;
-    AVCodecContext *enc, *video_enc;
+    AVCodecParameters *par, *video_par;
     int i, width, height /*, rate*/;
 
 /* XXX: do we reject audio streams or just ignore them ?
@@ -274,23 +274,23 @@ static int gif_write_header(AVFormatContext *s)
     gif->time      = 0;
     gif->file_time = 0;
 
-    video_enc = NULL;
+    video_par = NULL;
     for (i = 0; i < s->nb_streams; i++) {
-        enc = s->streams[i]->codec;
-        if (enc->codec_type != AVMEDIA_TYPE_AUDIO)
-            video_enc = enc;
+        par = s->streams[i]->codecpar;
+        if (par->codec_type != AVMEDIA_TYPE_AUDIO)
+            video_par = par;
     }
 
-    if (!video_enc) {
+    if (!video_par) {
         av_free(gif);
         return -1;
     } else {
-        width  = video_enc->width;
-        height = video_enc->height;
+        width  = video_par->width;
+        height = video_par->height;
 //        rate = video_enc->time_base.den;
     }
 
-    if (video_enc->pix_fmt != AV_PIX_FMT_RGB24) {
+    if (video_par->format != AV_PIX_FMT_RGB24) {
         av_log(s, AV_LOG_ERROR,
                "ERROR: gif only handles the rgb24 pixel format. Use -pix_fmt rgb24.\n");
         return AVERROR(EIO);
@@ -302,9 +302,10 @@ static int gif_write_header(AVFormatContext *s)
     return 0;
 }
 
-static int gif_write_video(AVFormatContext *s, AVCodecContext *enc,
+static int gif_write_video(AVFormatContext *s, AVStream *st,
                            const uint8_t *buf, int size)
 {
+    AVCodecParameters *par = st->codecpar;
     AVIOContext *pb = s->pb;
     int jiffies;
 
@@ -319,26 +320,26 @@ static int gif_write_video(AVFormatContext *s, AVCodecContext *enc,
     /* XXX: should use delay, in order to be more accurate */
     /* instead of using the same rounded value each time */
     /* XXX: don't even remember if I really use it for now */
-    jiffies = (70 * enc->time_base.num / enc->time_base.den) - 1;
+    jiffies = (70 * st->time_base.num / st->time_base.den) - 1;
 
     avio_wl16(pb, jiffies);
 
     avio_w8(pb, 0x1f); /* transparent color index */
     avio_w8(pb, 0x00);
 
-    gif_image_write_image(pb, 0, 0, enc->width, enc->height,
-                          buf, enc->width * 3, AV_PIX_FMT_RGB24);
+    gif_image_write_image(pb, 0, 0, par->width, par->height,
+                          buf, par->width * 3, AV_PIX_FMT_RGB24);
 
     return 0;
 }
 
 static int gif_write_packet(AVFormatContext *s, AVPacket *pkt)
 {
-    AVCodecContext *codec = s->streams[pkt->stream_index]->codec;
-    if (codec->codec_type == AVMEDIA_TYPE_AUDIO)
+    AVCodecParameters *par = s->streams[pkt->stream_index]->codecpar;
+    if (par->codec_type == AVMEDIA_TYPE_AUDIO)
         return 0; /* just ignore audio */
     else
-        return gif_write_video(s, codec, pkt->data, pkt->size);
+        return gif_write_video(s, s->streams[pkt->stream_index], pkt->data, pkt->size);
 }
 
 static int gif_write_trailer(AVFormatContext *s)