Hi Nicolas, On Mon, 2021-03-29 at 16:53 -0400, Nicolas Dufresne wrote: > Le lundi 29 mars 2021 à 15:13 -0300, Ezequiel Garcia a écrit : > > As stated in the MPEG-2 specification, section 6.3.7 "Quant matrix > > extension": > > > > Each quantisation matrix has a default set of values. When a > > sequence_header_code is decoded all matrices shall be reset to > > their default values. User defined matrices may be downloaded > > and this can occur in a sequence_header() or in a > > quant_matrix_extension(). > > > > The load_intra_quantiser_matrix syntax elements are transmitted > > in the bistream headers, signalling that a quantization matrix > quantisation > > Not really a typo, just a suggestion to follow the specification spelling. I > would like to see concistant spelling the API. My rational is that you can > copy > and paste the strings when searching inside the specification PDF, and you > don't > mix both in the API like we do now. >
Absolutely. Thanks for spotting this. > > needs to be loaded and used for pictures transmitted afterwards > > (until the matrices are reset). > > > > These "load" semantics are implemented in the V4L2 interface > > without the need of any "load" flags: passing the control > > is effectively a load. > > > > Therefore, rework the V4L2_CID_MPEG_VIDEO_MPEG2_QUANTIZATION > S > > > semantics to match the MPEG-2 semantics. Quantization matrices > s > > etc. > > > values are now initialized by the V4L2 control core to their > > reset default value, and applications are expected to reset > > their values as specified. > > > > The quantization control is therefore optional, and used to > > load bitstream-defined values in the quantization matrices. > > Perhaps: > > "The quantisation controls is therefore optional for decoding streams that > uses > the default matrices." > > A stack that would not handle the default, would have to read the control at > least once in order to avoid overriding valid values with 0s, not sure if that > is worth mentioning ? > Hm, not entirely sure. If application calls S_EXT_CTRL with 0s, then that's what will happen. Thanks, Ezequiel
