FFMPEG中protocol_list.c經過腳本產生

在FFMPEG源代碼中是沒有protocol_list.c定義的，是經過shell腳本產生。

1、configure中查找protocol_list.c

find_things_extern(){
    thing=$1
    pattern=$2
    file=$source_path/$3
    sed -n "s/^[^#]*extern.*$pattern *ff_\([^ ]*\)_$thing;/\1_$thing/p" "$file"
}

BSF_LIST=$(find_things_extern bsf AVBitStreamFilter libavcodec/bitstream_filters.c)
PROTOCOL_LIST=$(find_things_extern protocol URLProtocol libavformat/protocols.c)


enabled(){
    test "${1#!}" = "$1" && op='=' || op=!=
    eval test "x\$${1#!}" $op "xyes"
}



# generate the lists of enabled components
print_enabled_components(){
    file=$1
    struct_name=$2
    name=$3
    shift 3
    echo "static const $struct_name *$name[] = {" > $TMPH
    for c in $*; do
        enabled $c && printf "    &ff_%s,\n" $c >> $TMPH
    done 
    echo "    NULL };" >> $TMPH
    cp_if_changed $TMPH $file
}

print_enabled_components libavcodec/bsf_list.c AVBitStreamFilter bitstream_filters $BSF_LIST
print_enabled_components libavformat/protocol_list.c URLProtocol url_protocols $PROTOCOL_LIST

2、protocol_list.c內容

static const URLProtocol *url_protocols[] = { 
    &ff_async_protocol,
    &ff_cache_protocol,
    &ff_concat_protocol,
    &ff_crypto_protocol,
    &ff_data_protocol,
    &ff_ffrtmphttp_protocol,
    &ff_file_protocol,
    &ff_ftp_protocol,
    &ff_gopher_protocol,
    &ff_hls_protocol,
    &ff_http_protocol,
    &ff_httpproxy_protocol,
    &ff_icecast_protocol,
    &ff_mmsh_protocol,
    &ff_mmst_protocol,
    &ff_md5_protocol,
    &ff_pipe_protocol,
    &ff_rtmp_protocol,
    &ff_rtmpt_protocol,
    &ff_rtp_protocol,
    &ff_srtp_protocol,
    &ff_subfile_protocol,
    &ff_tee_protocol,
    &ff_tcp_protocol,
    &ff_udp_protocol,
    &ff_udplite_protocol,
    &ff_unix_protocol,
    NULL };

 

疑問：

protocols.c中有不少結構體URLProtocol，爲何只選擇了一部分？

extern const URLProtocol ff_async_protocol;
extern const URLProtocol ff_bluray_protocol;
extern const URLProtocol ff_cache_protocol;
extern const URLProtocol ff_concat_protocol;
extern const URLProtocol ff_crypto_protocol;
extern const URLProtocol ff_data_protocol;
extern const URLProtocol ff_ffrtmpcrypt_protocol;
extern const URLProtocol ff_ffrtmphttp_protocol;
extern const URLProtocol ff_file_protocol;
extern const URLProtocol ff_ftp_protocol;
extern const URLProtocol ff_gopher_protocol;
extern const URLProtocol ff_hls_protocol;
extern const URLProtocol ff_http_protocol;
extern const URLProtocol ff_httpproxy_protocol;
extern const URLProtocol ff_https_protocol;
extern const URLProtocol ff_icecast_protocol;
extern const URLProtocol ff_mmsh_protocol;
extern const URLProtocol ff_mmst_protocol;
extern const URLProtocol ff_md5_protocol;
extern const URLProtocol ff_pipe_protocol;
extern const URLProtocol ff_rtmp_protocol;
extern const URLProtocol ff_rtmpe_protocol;
extern const URLProtocol ff_rtmps_protocol;
extern const URLProtocol ff_rtmpt_protocol;
extern const URLProtocol ff_rtmpte_protocol;
extern const URLProtocol ff_rtmpts_protocol;
extern const URLProtocol ff_rtp_protocol;
extern const URLProtocol ff_sctp_protocol;
extern const URLProtocol ff_srtp_protocol;
extern const URLProtocol ff_subfile_protocol;
extern const URLProtocol ff_tee_protocol;
extern const URLProtocol ff_tcp_protocol;
extern const URLProtocol ff_tls_gnutls_protocol;
extern const URLProtocol ff_tls_schannel_protocol;
extern const URLProtocol ff_tls_securetransport_protocol;
extern const URLProtocol ff_tls_openssl_protocol;
extern const URLProtocol ff_udp_protocol;
extern const URLProtocol ff_udplite_protocol;
extern const URLProtocol ff_unix_protocol;
extern const URLProtocol ff_librtmp_protocol;
extern const URLProtocol ff_librtmpe_protocol;
extern const URLProtocol ff_librtmps_protocol;
extern const URLProtocol ff_librtmpt_protocol;
extern const URLProtocol ff_librtmpte_protocol;
extern const URLProtocol ff_libssh_protocol;
extern const URLProtocol ff_libsmbclient_protocol;