cache protocol unable to create temp files on windows 10

[Andrew Pearce]

Summary of the bug: when adding cache: in front of the URI, ffmpeg reports "failed to create tempfile".

How to reproduce:

Call avformat_open_input with cache: in front of the media URI

73 static int cache_open(URLContext *h, const char *arg, int flags, AVDictionary options)
74 {
75 char *buffername;
76 Context *c= h->priv_data;
77
78 av_strstart(arg, "cache:", &arg);
79
80 c->fd = avpriv_tempfile("ffcache", &buffername, 0, h);
81 if (c->fd < 0){
82 av_log(h, AV_LOG_ERROR, "Failed to create tempfile\n");
83 return c->fd;
84 }
85
86 unlink(buffername);
87 av_freep(&buffername);
88
89 return ffurl_open_whitelist(&c->inner, arg, flags, &h->interrupt_callback,
90 options, h->protocol_whitelist, h->protocol_blacklist, h);
91 }

FFmpeg output is:

FFmpeg (Error): [cache @ 0000021577e3d5c0] [TEMPFILE @ 00000092687fdd70] ff_tempfile: Cannot open temporary file ./ffcache1Apgjk

FFmpeg (Error): [cache @ 0000021577e3d700] [TEMPFILE @ 00000092660fe2e0] ff_tempfile: Cannot open temporary file ./ffcacheBoLLC0

FFmpeg (Error): [cache @ 0000021577e3d700] Failed to create tempfile

FFmpeg (Error): [cache @ 0000021577e3d5c0] Failed to create tempfile

[Carl Eugen Hoyos]

Please test current FFmpeg git head and provide the command line you tested together with the complete, uncut console output to make this a valid ticket.