avcodec/smvjpegdec: Make decoder init-threadsafe

The only thing that stands in the way of adding the
FF_CODEC_CAP_INIT_THREADSAFE flag to the SMV JPEG decoder is its usage
of ff_codec_open2_recursive(): This function requires its caller to hold
the lock for the mutex that guards initialization of AVCodecContexts
whose codecs have a non-threadsafe init function and only callers whose
codec does not have the FF_CODEC_CAP_INIT_THREADSAFE flag set hold said
lock (the others don't need to care about said lock). But one can set
the flag if one switches to avcodec_open2() at the same time.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/smvjpegdec.c

@@ -129,7 +129,7 @@ static av_cold int smvjpeg_decode_init(AVCodecContext *avctx)
     s->avctx->refcounted_frames = 1;
     s->avctx->flags = avctx->flags;
     s->avctx->idct_algo = avctx->idct_algo;
-    if ((r = ff_codec_open2_recursive(s->avctx, codec, &thread_opt)) < 0) {
+    if ((r = avcodec_open2(s->avctx, codec, &thread_opt)) < 0) {
         av_log(avctx, AV_LOG_ERROR, "MJPEG codec failed to open\n");
         ret = r;
     }
@@ -220,4 +220,5 @@ AVCodec ff_smvjpeg_decoder = {
     .close          = smvjpeg_decode_end,
     .decode         = smvjpeg_decode_frame,
     .priv_class     = &smvjpegdec_class,
+    .caps_internal  = FF_CODEC_CAP_INIT_THREADSAFE,
 };