[FFmpeg-devel] [GSOC] [PATCH] SRCNN filter

[Michael Niedermayer]

On Wed, Mar 28, 2018 at 11:17:40AM +0300, Sergey Lavrushkin wrote:
> > [...]
> > > +#define OFFSET(x) offsetof(SRCNNContext, x)
> > > +#define FLAGS AV_OPT_FLAG_FILTERING_PARAM | AV_OPT_FLAG_VIDEO_PARAM
> > > +static const AVOption srcnn_options[] = {
> > > +    { "config_file", "path to configuration file with network
> > parameters", OFFSET(config_file_path), AV_OPT_TYPE_STRING, {.str=NULL}, 0,
> > 0, FLAGS },
> > > +    { NULL }
> > > +};
> > > +
> > > +AVFILTER_DEFINE_CLASS(srcnn);
> > > +
> > > +#define CHECK_FILE(file)    if (ferror(file) || feof(file)){ \
> > > +                                av_log(context, AV_LOG_ERROR, "error
> > reading configuration file\n");\
> > > +                                fclose(file); \
> > > +                                return AVERROR(EIO); \
> > > +                            }
> > > +
> > > +#define CHECK_ALLOCATION(conv, file)    if
> > (allocate_and_read_convolution_data(&conv, file)){ \
> > > +                                            av_log(context,
> > AV_LOG_ERROR, "could not allocate memory for convolutions\n"); \
> > > +                                            fclose(file); \
> > > +                                            return AVERROR(ENOMEM); \
> > > +                                        }
> > > +
> >
> > > +static int allocate_and_read_convolution_data(Convolution* conv, FILE*
> > config_file)
> > > +{
> > > +    int32_t kernel_size = conv->output_channels * conv->size *
> > conv->size * conv->input_channels;
> > > +    conv->kernel = av_malloc(kernel_size * sizeof(double));
> > > +    if (!conv->kernel){
> > > +        return 1;
> >
> > this should return an AVERROR code for consistency with the rest of
> > the codebase
> >
> 
> Ok.
> 
> 
> > > +    }
> >
> > > +    fread(conv->kernel, sizeof(double), kernel_size, config_file);
> >
> > directly reading data types is not portable, it would for example be
> > endian specific
> > and using avio for reading may be better, though fread is as far as iam
> > concerned also ok
> >
> 
> Ok, I understand the problem, but I have not really worked with it before,
> so I need an advice of how to properly fix it. If I understand correctly,
> for

> int32_t I need to check endianness and reverse bytes if necessary. But with

see avio_rb32()
might not be as fast as reading a whole array and byteswaping though.
Not sure it matters


> doubles it is more complicated. Should I write a IEEE 754 converter from
> binary
> to double or maybe I can somehow check IEEE 754 doubles support and
> depending
> on it either stick to the default network weights, or just read bytes and
> check
> endianness, if IEEE 754 doubles are supported? Or maybe avio provide some
> utility to deal with this problem?

something like this should work:
av_int2float(avio_rb32(pb));
av_int2double(avio_rb64(pb));

> 
> 
> > [...]
> > > +/**
> > > + * @file
> > > + * Default cnn weights for x2 upsampling with srcnn filter.
> > > + */
> > > +
> > > +/// First convolution kernel
> >
> > > +static double conv1_kernel[] = {
> >
> > static data should be also const, otherwise it may be changed and could
> > cause
> > thread saftey issues
> >
> 
> Ok, I just wanted to not allocate additional memory in case of using
> default weights.

well, there can be more than one instance of a filter running at the same time
so static variables that are actually changing will affect the other
filter instance


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When the tyrant has disposed of foreign enemies by conquest or treaty, and
there is nothing more to fear from them, then he is always stirring up
some war or other, in order that the people may require a leader. -- Plato
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