[Bug 781748] New: One frame delayed in vaapidecode when playing h264.

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=781748

            Bug ID: 781748
           Summary: One frame delayed in vaapidecode when playing h264.
    Classification: Platform
           Product: GStreamer
           Version: unspecified
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gstreamer-vaapi
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: njh5320752 at gmail.com
        QA Contact: gstreamer-bugs at lists.freedesktop.org
                CC: bsreerenj at gmail.com, vjaquez at igalia.com
     GNOME version: ---

Created attachment 350431
  --> https://bugzilla.gnome.org/attachment.cgi?id=350431&action=edit
h264 file

In the log, DPB size is 1.
So I expect to be decoded as soon as IDR slice or non-IDR slice push to
vaapidecode.
But in the log, vaapidecode doesn't decode a frame when received IDR slice.
And then vaapidecode is received 1st non-IDR slice, vaapidecode decode one
frame.(I guess this frame is IDR's picture)
And then vaapidecode is received 2nd non-IDR slice, vaapidecode decode one
frame.(I guess this frame is 1st non-IDR's picture)
....
This is repeated.

That's why I think that vaapidecode is delayed one frame.
This can become the problem in real-time streaming such as Android Auto or
Carplay.
Because the last frame does not display always when playing.


vaapi gstvaapidecoder_h264.c:1037:dpb_reset:^[[00m DPB size 1
vaapi gstvaapidecoder_h264.c:2878:init_picture:^[[00m <IDR>
vaapi gstvaapidecoder_h264.c:3697:decode_slice:^[[00m slice (1511 bytes)
vaapi gstvaapidecoder_objects.c:241:gst_vaapi_picture_decode:^[[00m decode
picture 0x04000000
vaapi gstvaapidecoder_h264.c:3697:decode_slice:^[[00m slice (6 bytes)
vaapi gstvaapidecoder_objects.c:241:gst_vaapi_picture_decode:^[[00m decode
picture 0x04000001
vaapi gstvaapidecoder.c:378:push_frame:^[[00m push frame 0 (surface 0x04000000)
vaapi gstvaapidecoder.c:399:pop_frame:^[[00m pop frame 0 (surface 0x04000000)
vaapi gstvaapidecoder_h264.c:3697:decode_slice:^[[00m slice (751 bytes)
vaapi gstvaapidecoder_objects.c:241:gst_vaapi_picture_decode:^[[00m decode
picture 0x04000002
vaapi gstvaapidecoder.c:378:push_frame:^[[00m push frame 1 (surface 0x04000001)
vaapi gstvaapidecoder.c:399:pop_frame:^[[00m pop frame 1 (surface 0x04000001)
....

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