avformat/ffmenc: Make ffm_write_header_codec_ctx() use codecpar

This would be simpler if codecpar supported AVOptions
modern ffserver should be unaffected by this, older ffserver which required the
muxer to directly access the encoder could have issues with this, but this
direct access is just wrong and unsafe
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/ffmenc.c

@@ -95,11 +95,12 @@ static void write_header_chunk(AVIOContext *pb, AVIOContext *dpb, unsigned id)
     av_free(dyn_buf);
 }
 
-static int ffm_write_header_codec_ctx(AVIOContext *pb, AVCodecContext *ctx, unsigned tag, int type)
+static int ffm_write_header_codec_ctx(AVIOContext *pb, AVCodecParameters *ctxpar, unsigned tag, int type)
 {
     AVIOContext *tmp;
     char *buf = NULL;
     int ret, need_coma = 0;
+    AVCodecContext *ctx = NULL;
 
 #define SKIP_DEFAULTS   AV_OPT_SERIALIZE_SKIP_DEFAULTS
 #define OPT_FLAGS_EXACT AV_OPT_SERIALIZE_OPT_FLAGS_EXACT
@@ -107,6 +108,16 @@ static int ffm_write_header_codec_ctx(AVIOContext *pb, AVCodecContext *ctx, unsi
 
     if (avio_open_dyn_buf(&tmp) < 0)
         return AVERROR(ENOMEM);
+
+    // AVCodecParameters does not suport AVOptions, we thus must copy it over to a context that does
+    // otherwise it could be used directly and this would be much simpler
+    ctx = avcodec_alloc_context3(NULL);
+    if (!ctx) {
+        ret = AVERROR(ENOMEM);
+        goto fail;
+    }
+    avcodec_parameters_to_context(ctx, ctxpar);
+
     if ((ret = av_opt_serialize(ctx, ENC | type, SKIP_DEFAULTS, &buf, '=', ',')) < 0)
         goto fail;
     if (buf && strlen(buf)) {
@@ -124,10 +135,12 @@ static int ffm_write_header_codec_ctx(AVIOContext *pb, AVCodecContext *ctx, unsi
     av_freep(&buf);
     avio_w8(tmp, 0);
     write_header_chunk(pb, tmp, tag);
+    avcodec_free_context(&ctx);
     return 0;
   fail:
     av_free(buf);
     ffio_free_dyn_buf(&tmp);
+    avcodec_free_context(&ctx);
     return ret;
 
 #undef SKIP_DEFAULTS
@@ -261,7 +274,7 @@ static int ffm_write_header(AVFormatContext *s)
                 if ((ret = ffm_write_recommended_config(s->pb, codec, MKBETAG('S', '2', 'V', 'I'),
                                                         st->recommended_encoder_configuration)) < 0)
                 return ret;
-            } else if ((ret = ffm_write_header_codec_ctx(s->pb, codec, MKBETAG('S', '2', 'V', 'I'), AV_OPT_FLAG_VIDEO_PARAM)) < 0)
+            } else if ((ret = ffm_write_header_codec_ctx(s->pb, codecpar, MKBETAG('S', '2', 'V', 'I'), AV_OPT_FLAG_VIDEO_PARAM)) < 0)
                 return ret;
             break;
         case AVMEDIA_TYPE_AUDIO:
@@ -271,7 +284,7 @@ static int ffm_write_header(AVFormatContext *s)
                 if ((ret = ffm_write_recommended_config(s->pb, codec, MKBETAG('S', '2', 'A', 'U'),
                                                         st->recommended_encoder_configuration)) < 0)
                 return ret;
-            } else if ((ret = ffm_write_header_codec_ctx(s->pb, codec, MKBETAG('S', '2', 'A', 'U'), AV_OPT_FLAG_AUDIO_PARAM)) < 0)
+            } else if ((ret = ffm_write_header_codec_ctx(s->pb, codecpar, MKBETAG('S', '2', 'A', 'U'), AV_OPT_FLAG_AUDIO_PARAM)) < 0)
                 return ret;
             break;
         default:

tests/ref/lavf/ffm

-03f2673a39a9494157eb4be9af537f84 *./tests/data/lavf/lavf.ffm
+a0e9616f0d9a8c1029f3220b1b9175f4 *./tests/data/lavf/lavf.ffm
 376832 ./tests/data/lavf/lavf.ffm
 ./tests/data/lavf/lavf.ffm CRC=0x000e23ae