Re: [FFmpeg-devel] [PATCH v2 2/2] avformat/rtmpproto: support enhanced rtmp

[Steven Liu <lingjiujianke@gmail.com>]

Martin Storsjö <martin@martin.st> 于2023年8月25日周五 17:38写道：
>
> On Fri, 25 Aug 2023, Steven Liu wrote:
>
> >> > +        list_len = (fourcc_str_len + 1) / 5;
> >> > +        // write the fourCcList field name
> >> > +        ff_amf_write_field_name(&p, "fourCcList");
> >> > +
> >> > +        // write the fourcc array length
> >> > +        ff_amf_write_array_start(&p, list_len);
> >> > +
> >> > +        while(fourcc_data - rt->enhanced_codecs < fourcc_str_len) {
> >> > +            unsigned char fourcc[5];
> >> > +            switch (AV_RN32(fourcc_data)) {
> >> > +                case MKTAG('h', 'v', 'c', '1'):
> >>
> >> This feels a bit convoluted to use AV_RN32 + MKTAG on data that is already
> >> just a string - just using strncmp(fourcc_data, "hvc1", 4) would work just
> > I want use strncmp at first, but i think strncmp will slower than
> > switch uint32_t value, so i chose use uint32_t. or should i use
> > strncmp?
>
> Yes, strncmp will be slower than switching on an uint32_t - but this isn't
> really performance sensitive code. We do this once only, on startup, on a
> handful of fourccs. So I believe code clarity is more important than
> absolute performance here.
Okay, i use strncasecmp next version patch. But i must told you, I
think MKTAG is clarity than use if+strncmp to me,
Because there looks like a fourcc codec list align code block.
>
> // Martin
>
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