[Bug 732266] vaapidecode: h264: add support for decoding SVC base layers only

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=732266

Orestis Floros <orestisf1993 at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
 Attachment #358041|reviewed                    |none
             status|                            |
 Attachment #358041|0                           |1
        is obsolete|                            |

--- Comment #34 from Orestis Floros <orestisf1993 at gmail.com> ---
Created attachment 358103
  --> https://bugzilla.gnome.org/attachment.cgi?id=358103&action=edit
libs: decoder: h264: decode SVC base view only

(In reply to sreerenj from comment #33)
> Review of attachment 358041 [details] [review]:
>
> ::: gst-libs/gst/vaapi/gstvaapidecoder_h264.c
> @@ +1793,3 @@
>
> +  if (priv->base_only && !GST_H264_IS_MVC_NALU (&pi->nalu))
> +    result = gst_h264_parse_sps (&pi->nalu, sps, FALSE);
>
> Why does it only for SVC? svc and mvc base-only mode should behave
> similarly. right?

I don't know how I missed it, this part is buggy and breaks MVC streams with
base-only=TRUE right now. This patch should do it.

I don't know why they behave differently here, I made the distinction through
trial and error.

> @@ +1941,3 @@
>    GST_DEBUG ("decode subset SPS");
>
> +  /* Don't replace. Could overwrite needeed SPS's. */
>
> Bit confused with this comment. I understood that in base-only case, we
> don't have to store the subset_sps. But when can this "Overwrite needed sps"
> happen?

spec says:

> NOTE 7 ? A decoder must be capable of simultaneously storing the contents of the sequence parameter sets and subset sequence
parameter sets for all values of seq_parameter_set_id. The content of the
sequence parameter set with a particular value of
seq_parameter_set_id is overwritten when a new sequence parameter set NAL unit
with the same value of seq_parameter_set_id is
received, and the content of the subset sequence parameter set with a
particular value of seq_parameter_set_id is overwritten when
a new subset sequence parameter set NAL unit with the same value of
seq_parameter_set_id is received.

Eg in SVCHS-2.264:
nalu type=7 has seq_parameter_set_id=0 and next nalu type=15 has
seq_parameter_set_id=0.

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