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

From: "Martin Storsjö" <martin@martin.st>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Cc: Steven Liu <lq@chinaffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH v2 2/2] avformat/rtmpproto: support enhanced rtmp
Date: Fri, 25 Aug 2023 12:38:27 +0300 (EEST)
Message-ID: <49a65bba-634c-1afb-6c52-94565bd7cc9@martin.st> (raw)
In-Reply-To: <CADxeRwmzCS-pZ8CoWZDLD0t9VQEY1fBv4ejUbtxqKOphbUw==Q@mail.gmail.com>

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.

// Martin

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