Rename variables:

pass_logfilename -> pass_logfilename_prefix
DEFAULT_PASS_LOGFILENAME -> DEFAULT_PASS_LOGFILENAME_PREFIX

and make clear in the passlogfile OptionDef help string that it takes
a file name prefix rather than a file name.

Originally committed as revision 16350 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffmpeg.c

@@ -183,7 +183,7 @@ static int do_hex_dump = 0;
 static int do_pkt_dump = 0;
 static int do_psnr = 0;
 static int do_pass = 0;
-static char *pass_logfilename = NULL;
+static char *pass_logfilename_prefix = NULL;
 static int audio_stream_copy = 0;
 static int video_stream_copy = 0;
 static int subtitle_stream_copy = 0;
@@ -232,7 +232,7 @@ static AVBitStreamFilterContext *audio_bitstream_filters=NULL;
 static AVBitStreamFilterContext *subtitle_bitstream_filters=NULL;
 static AVBitStreamFilterContext *bitstream_filters[MAX_FILES][MAX_STREAMS];
 
-#define DEFAULT_PASS_LOGFILENAME "ffmpeg2pass"
+#define DEFAULT_PASS_LOGFILENAME_PREFIX "ffmpeg2pass"
 
 struct AVInputStream;
 
@@ -1837,8 +1837,8 @@ static int av_encode(AVFormatContext **output_files,
                 char *logbuffer;
 
                 snprintf(logfilename, sizeof(logfilename), "%s-%d.log",
-                         pass_logfilename ?
-                         pass_logfilename : DEFAULT_PASS_LOGFILENAME, i);
+                         pass_logfilename_prefix ?
+                         pass_logfilename_prefix : DEFAULT_PASS_LOGFILENAME_PREFIX, i);
                 if (codec->flags & CODEC_FLAG_PASS1) {
                     f = fopen(logfilename, "w");
                     if (!f) {
@@ -3797,7 +3797,7 @@ static const OptionDef options[] = {
     { "sameq", OPT_BOOL | OPT_VIDEO, {(void*)&same_quality},
       "use same video quality as source (implies VBR)" },
     { "pass", HAS_ARG | OPT_VIDEO, {(void*)&opt_pass}, "select the pass number (1 or 2)", "n" },
-    { "passlogfile", HAS_ARG | OPT_STRING | OPT_VIDEO, {(void*)&pass_logfilename}, "select two pass log file name", "file" },
+    { "passlogfile", HAS_ARG | OPT_STRING | OPT_VIDEO, {(void*)&pass_logfilename_prefix}, "select two pass log file name prefix", "prefix" },
     { "deinterlace", OPT_BOOL | OPT_EXPERT | OPT_VIDEO, {(void*)&do_deinterlace},
       "deinterlace pictures" },
     { "psnr", OPT_BOOL | OPT_EXPERT | OPT_VIDEO, {(void*)&do_psnr}, "calculate PSNR of compressed frames" },