mpeg2decoder: fail early if no input caps have been provided

The mpeg2decoder class does not implement the ->parse() virtual function,
and we always need to add the mpegvideoparse element before it. So we should
set_needs_format of the decoder to TRUE, then if no parse before it, it
can fail with a "not-negotiated" error early, rather than go on and
generate unexpected error.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4066>

diff --git a/subprojects/gst-plugins-bad/gst-libs/gst/codecs/gstmpeg2decoder.c b/subprojects/gst-plugins-bad/gst-libs/gst/codecs/gstmpeg2decoder.c
index 7a45be6..d0fefce 100644 (file)
--- a/subprojects/gst-plugins-bad/gst-libs/gst/codecs/gstmpeg2decoder.c
+++ b/subprojects/gst-plugins-bad/gst-libs/gst/codecs/gstmpeg2decoder.c
@@ -329,6 +329,7 @@ static void
 gst_mpeg2_decoder_init (GstMpeg2Decoder * self)
 {
   gst_video_decoder_set_packetized (GST_VIDEO_DECODER (self), TRUE);
+  gst_video_decoder_set_needs_format (GST_VIDEO_DECODER (self), TRUE);
 
   self->priv = gst_mpeg2_decoder_get_instance_private (self);