amf: Replace writer_id option with LIBAV_AMF_WRITER_ID constant

AMFTraceWriter is an abstraction to configure how AMF outputs its logs
for the current process and can be configured to output different levels
of trace output. If multiple LibavWriter objects are used in one process,
there will be duplication of output in av_log. Use a constant writer_id
to prevent this scenario.
Signed-off-by: Diego Biurrun <diego@biurrun.de>

libavcodec/amfenc.c

@@ -46,6 +46,8 @@
 #include <dlfcn.h>
 #endif
 
+#define LIBAV_AMF_WRITER_ID L"libav_log"
+
 #define PTS_PROP L"PtsProp"
 
 const enum AVPixelFormat ff_amf_pix_fmts[] = {
@@ -171,8 +173,8 @@ static int amf_init_context(AVCodecContext *avctx)
     // connect AMF logger to av_log
     ctx->tracer.vtbl = &tracer_vtbl;
     ctx->tracer.avctx = avctx;
-    ctx->trace->pVtbl->RegisterWriter(ctx->trace, ctx->writer_id, (AMFTraceWriter*)&ctx->tracer, 1);
-    ctx->trace->pVtbl->SetWriterLevel(ctx->trace, ctx->writer_id, AMF_TRACE_TRACE);
+    ctx->trace->pVtbl->RegisterWriter(ctx->trace, LIBAV_AMF_WRITER_ID,(AMFTraceWriter *)&ctx->tracer, 1);
+    ctx->trace->pVtbl->SetWriterLevel(ctx->trace, LIBAV_AMF_WRITER_ID, AMF_TRACE_TRACE);
 
     res = ctx->factory->pVtbl->CreateContext(ctx->factory, &ctx->context);
     AMF_RETURN_IF_FALSE(ctx, res == AMF_OK, AVERROR_UNKNOWN, "CreateContext() failed with error %d\n", res);
@@ -283,7 +285,7 @@ int av_cold ff_amf_encode_close(AVCodecContext *avctx)
     av_buffer_unref(&ctx->hw_frames_ctx);
 
     if (ctx->trace) {
-        ctx->trace->pVtbl->UnregisterWriter(ctx->trace, ctx->writer_id);
+        ctx->trace->pVtbl->UnregisterWriter(ctx->trace, LIBAV_AMF_WRITER_ID);
     }
     if (ctx->library) {
         dlclose(ctx->library);

libavcodec/amfenc.h

@@ -80,7 +80,6 @@ typedef struct AmfContext {
 
     // common encoder options
     int                 log_to_dbg;
-    char                *writer_id;
 
     // Static options, have to be set before Init() call
     int                 usage;
@@ -152,7 +151,6 @@ extern const enum AVPixelFormat ff_amf_pix_fmts[];
     }
 
 #define AMF_COMMON_OPTIONS \
-    { "log_to_dbg",     "Enable AMF logging to debug output",   OFFSET(log_to_dbg), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 1, VE }, \
-    { "writer_id",      "Enable AMF logging to writer id",      OFFSET(writer_id),  AV_OPT_TYPE_STRING, { .str = "libavcodec" }, 0, 1, VE } \
+    { "log_to_dbg",     "Enable AMF logging to debug output",   OFFSET(log_to_dbg), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 1, VE } \
 
 #endif //AVCODEC_AMFENC_H