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codecs: h264decoder: update max_dpb_frames only if VUI is present

Víctor Manuel Jáquez Leal requested to merge vjaquez/gst-plugins-bad:max-dpb-frames into master

There are some streams, with HRD, where the the calculated max_dpb_frames is zero (max_dpb_mbs is less than size mb). In order to get the dbp size it is required to rely on the VUI parameters if they are present.

According to the spec Annex E.2.1

max_dec_frame_buffering specifies the required size of the HRD decoded picture buffer (DPB) in units of frame buffers. It is a requirement of bitstream conformance that the coded video sequence shall not require a decoded picture buffer with size of more than Max(1, max_dec_frame_buffering) frame buffers to enable the output of decoded pictures at the output times specified by dpb_output_delay of the picture timing SEI messages. The value of max_dec_frame_buffering shall be greater than or equal to max_num_ref_frames. An upper bound for the value of max_dec_frame_buffering is specified by the level limits in clauses A.3.1, A.3.2, G.10.2.1, and H.10.2.

When the max_dec_frame_buffering syntax element is not present, the value of max_dec_frame_buffering shall be inferred as follows:

– If profile_idc is equal to 44, 86, 100, 110, 122, or 244 and constraint_set3_flag is equal to 1, the value of max_dec_frame_buffering shall be inferred to be equal to 0.

– Otherwise (profile_idc is not equal to 44, 86, 100, 110, 122, or 244 or constraint_set3_flag is equal to 0), the value of max_dec_frame_buffering shall be inferred to be equal to MaxDpbFrames.

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