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

[Martin Storsjö]

On Fri, 25 Aug 2023, Steven Liu wrote:

> Add option named rtmp_enhanced_codec,
> it would support hvc1,av01,vp09 now,
> the fourcc is using Array of strings.
>
> Signed-off-by: Steven Liu <lq at chinaffmpeg.org>
> ---
> doc/protocols.texi      |  6 ++++++
> libavformat/rtmpproto.c | 35 +++++++++++++++++++++++++++++++++++
> 2 files changed, 41 insertions(+)
>
> diff --git a/doc/protocols.texi b/doc/protocols.texi
> index b3fad55591..bd2b25e502 100644
> --- a/doc/protocols.texi
> +++ b/doc/protocols.texi
> @@ -896,6 +896,12 @@ be named, by prefixing the type with 'N' and specifying the name before
> the value (i.e. @code{NB:myFlag:1}). This option may be used multiple
> times to construct arbitrary AMF sequences.
>
> + at item rtmp_enhanced_codecs
> +Specify the list of codecs the client advertises to support in an
> +enhanced RTMP stream. This option should set a string like @code{hvc1,av01,vp09}
> +for multiple codecs, or @code{hvc1} for only one codec,
> +set codec fourcc into fourCcLive property into Connect Command Message,
> +
> @item rtmp_flashver
> Version of the Flash plugin used to run the SWF player. The default
> is LNX 9,0,124,2. (When publishing, the default is FMLE/3.0 (compatible;
> diff --git a/libavformat/rtmpproto.c b/libavformat/rtmpproto.c
> index f0ef223f05..ea25454362 100644
> --- a/libavformat/rtmpproto.c
> +++ b/libavformat/rtmpproto.c
> @@ -127,6 +127,7 @@ typedef struct RTMPContext {
>     int           nb_streamid;                ///< The next stream id to return on createStream calls
>     double        duration;                   ///< Duration of the stream in seconds as returned by the server (only valid if non-zero)
>     int           tcp_nodelay;                ///< Use TCP_NODELAY to disable Nagle's algorithm if set to 1
> +    char          *enhanced_codecs;           ///< codec list in enhanced rtmp
>     char          username[50];
>     char          password[50];
>     char          auth_params[500];
> @@ -336,6 +337,39 @@ static int gen_connect(URLContext *s, RTMPContext *rt)
>     ff_amf_write_field_name(&p, "app");
>     ff_amf_write_string2(&p, rt->app, rt->auth_params);
>
> +    if (rt->enhanced_codecs) {
> +        uint32_t list_len = 0;
> +        char *fourcc_data = rt->enhanced_codecs;
> +        int fourcc_str_len = strlen(fourcc_data);
> +
> +        // check the string, fourcc + ',' + ...  + end fourcc correct length should be (4+1)*n+4
> +        if ((fourcc_str_len + 1) % 5 != 0)
> +            return AVERROR(EINVAL);

If we trigger this error, we definitely should tell the user what was 
wrong. 'Malformed rtmp_enhanched_codecs, should be of the form 
"fourcc[,fourcc..]"' or something like that? (Would it be better to use 
"frcc" or just "hvc1" or something else there, to show that it needs to be 
exactly a four char string for each element?)

> +
> +        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 
as well. That doesn't fit quite as neatly into a switch, but would be a 
more unwieldy if statement though.

> +                case MKTAG('a', 'v', '0', '1'):
> +                case MKTAG('v', 'p', '0', '9'):
> +                    av_strlcpy(fourcc, fourcc_data, sizeof(fourcc));
> +                    ff_amf_write_string(&p, fourcc);
> +                    break;
> +                default:

When this fails, the user definitely needs to know what was wrong, so we 
should print the string that didn't match the expectation. E.g. 
("unsupported codec fourcc, %.*s", 4, fourcc_data) or something like that?

// Martin