[Bug 786802] vaapidecode: h264: fix nal aligned streams

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=786802

Hyunjun Ko <zzoon at igalia.com> changed:

           What    |Removed                     |Added
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                 CC|                            |zzoon at igalia.com

--- Comment #2 from Hyunjun Ko <zzoon at igalia.com> ---
I've looked into this issue all this week.
This is a bit tricky but let me try to explain briefly.

1. This is introduced by my commit to gsth264parse (201e71c in gst-plugins-bad)
Since the commit landed, incoming data with byte-stream/nal is like:
<AU><SLICE> instead of just only <SLICE>.
vaapih264dec can't handle this now, which is this issue.

2. I think vaapih264dec is doing fine in the way it should do.
Adding AU to a frame and adding SLICE to the frame (by add_to_frame)
and have_frame call.

3. Meanwhile, in the base video decoder, it tries to decide frame information
such as pts, duration, etc. See gst_video_decoder_get_buffer_info_at_offset.
Previously it choose info from slice buffer properly, but for now it choose
from AU buffer.

Finally this wrong information leads to dropping all frames in
gst_video_decoder_clip_and_push_buf.

Acutally, I tried to improve gst_video_decoder_get_buffer_info_at_offset, but I
realized that I have to be careful since there are lots of cases.

Now I'm looking for other solution. :(

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