threads: change the default for threads back to 1

Using threaded decoding by default breaks backward compatibility if
AVHWAccel is used or if an appliction sets threadunsafe callbacks.
Avconv and avplay still use -threads auto if not specified.

avconv.c

@@ -2210,6 +2210,8 @@ static int init_input_stream(int ist_index, OutputStream *output_streams, int nb
             ist->st->codec->opaque         = ist;
         }
 
+        if (!av_dict_get(ist->opts, "threads", NULL, 0))
+            av_dict_set(&ist->opts, "threads", "auto", 0);
         if (avcodec_open2(ist->st->codec, codec, &ist->opts) < 0) {
             snprintf(error, error_len, "Error while opening decoder for input stream #%d:%d",
                     ist->file_index, ist->st->index);
@@ -2512,6 +2514,8 @@ static int transcode_init(OutputFile *output_files,
                 memcpy(ost->st->codec->subtitle_header, dec->subtitle_header, dec->subtitle_header_size);
                 ost->st->codec->subtitle_header_size = dec->subtitle_header_size;
             }
+            if (!av_dict_get(ost->opts, "threads", NULL, 0))
+                av_dict_set(&ost->opts, "threads", "auto", 0);
             if (avcodec_open2(ost->st->codec, codec, &ost->opts) < 0) {
                 snprintf(error, sizeof(error), "Error while opening encoder for output stream #%d:%d - maybe incorrect parameters such as bit_rate, rate, width or height",
                         ost->file_index, ost->index);

avplay.c

@@ -2194,6 +2194,8 @@ static int stream_component_open(VideoState *is, int stream_index)
     if (lowres) avctx->flags  |= CODEC_FLAG_EMU_EDGE;
     if (fast)   avctx->flags2 |= CODEC_FLAG2_FAST;
 
+    if (!av_dict_get(opts, "threads", NULL, 0))
+        av_dict_set(&opts, "threads", "auto", 0);
     if (!codec ||
         avcodec_open2(avctx, codec, &opts) < 0)
         return -1;

libavcodec/options.c

@@ -372,7 +372,7 @@ static const AVOption options[]={
 {"float", NULL, 0, AV_OPT_TYPE_CONST, {.dbl = FF_AA_FLOAT }, INT_MIN, INT_MAX, V|D, "aa"},
 #endif
 {"qns", "quantizer noise shaping", OFFSET(quantizer_noise_shaping), AV_OPT_TYPE_INT, {.dbl = DEFAULT }, INT_MIN, INT_MAX, V|E},
-{"threads", NULL, OFFSET(thread_count), AV_OPT_TYPE_INT, {.dbl = 0 }, 0, INT_MAX, V|E|D, "threads"},
+{"threads", NULL, OFFSET(thread_count), AV_OPT_TYPE_INT, {.dbl = 1 }, 0, INT_MAX, V|E|D, "threads"},
 {"auto", "detect a good number of threads", 0, AV_OPT_TYPE_CONST, {.dbl = 0 }, INT_MIN, INT_MAX, V|E|D, "threads"},
 {"me_threshold", "motion estimaton threshold", OFFSET(me_threshold), AV_OPT_TYPE_INT, {.dbl = DEFAULT }, INT_MIN, INT_MAX, V|E},
 {"mb_threshold", "macroblock threshold", OFFSET(mb_threshold), AV_OPT_TYPE_INT, {.dbl = DEFAULT }, INT_MIN, INT_MAX, V|E},