diff --git a/teetime/teetime b/teetime/teetime
index 331f441..dad3481 100755
--- a/teetime/teetime
+++ b/teetime/teetime
@@ -44,7 +44,7 @@ Play back I<factor> times faster. 1.0 = actual speed.
 
 =item B<-i>
 
-Read I<file> as input.
+Read I<file> as input. Use - to read from standard input.
 
 
 =item B<--maxwait> I<maxwait>
@@ -53,19 +53,39 @@ Read I<file> as input.
 
 Wait at most I<maxwait> seconds.
 
-
-
 =back
 
+
 =head1 EXAMPLES
 
-  (sleep 0.5; echo After 0.5s; sleep 1.5; echo After 2s) | teetime myfile
-  (sleep 0.5; echo After 2.5s; sleep 1.5; echo After 4s) | teetime -a myfile
-  teetime -i myfile
+  (sleep 0.5; echo After 0.5s; sleep 1.5; echo After 2s) |
+    teetime myfile.tt
+  (sleep 0.5; echo After 2.5s; sleep 1.5; echo After 4s) |
+    teetime -a myfile.tt
+  teetime -i myfile.tt
+
+Play file using stdin:
+
+  cat myfile.tt | teetime -i -
+
+Play it faster:
+
+  teetime -f 2 -i myfile.tt
+
+=head1 File format
+
+The .tt-format is simply:
+
+  Version: "TTM1"
+  Repeat: (
+    Wait ms: Unsigned 32-bit
+    Length of string: Unsigned 32-bit
+    String: string
+  )
 
 =head1 AUTHOR
 
-Copyright (C) 2020 Ole Tange,
+Copyright (C) 2020-2023 Ole Tange,
 http://ole.tange.dk and Free Software Foundation, Inc.
 
 
@@ -99,16 +119,39 @@ B<tee>
 
 =cut
 
+sub bashtest1 {
+    q{
+	rand -s 8 | head -c 1G | teetime - |mbuffer -q | teetime -i - | pv | md5sum
+	rand -s 8 | head -c 1G | pv | md5sum
+    };
+}
+
+sub bashtest2 {
+    q{
+	doit() {
+	    diff <(rand -s $1 |
+		       head -c$1 |
+		       md5sum) <(rand -s $1 |
+				     teetime - |
+				     teetime -i - |
+				     head -c$1 |
+				     md5sum);
+	}
+	export -f doit
+	find-first-fail -v doit
+    };
+}
+
 use strict;
 
 use Getopt::Long;
 
 sub now {
-    # Returns time since epoch as in seconds with 3 decimals
+    # Returns time since epoch in ms
     # Uses:
     #   @Global::use
     # Returns:
-    #   $time = time now with millisecond accuracy
+    #   $time = in milliseconds
     if(not $Global::use{"Time::HiRes"}) {
 	if(eval "use Time::HiRes qw ( time );") {
 	    eval "sub TimeHiRestime { return Time::HiRes::time };";
@@ -122,22 +165,34 @@ sub now {
 }
 
 sub readstdin {
+    # Read stdin and save it in .tt-format
+    # If no file: save to stdout, but do not tee output
     my $file = shift;
-    my $last_time = now();    
+    my $last_time = now();
     my $rin = '';
     my $in;
-    my $twogb = 2**31;
     my ($read, $time, $delta);
-    open(my $fh, ($opt::append ? ">>" : ">"), $file) || die;
-    
+    my $fh;
+    my $save_to_stdout;
+    if(not defined $file or $file eq "-") {
+	$save_to_stdout = 1;
+    }
+    if($save_to_stdout) {
+	$fh = *STDOUT;
+	$| = 1;
+    } else {
+	open($fh, ($opt::append ? ">>" : ">"), $file) || die;
+    }
     vec($rin, fileno(STDIN), 1) = 1;
+    # print FourCC file identifier
+    print $fh "TTM1";
     while(1) {
 	select($rin,undef,undef,undef);
-	$read = sysread(STDIN,$in,$twogb);
+	$read = sysread(STDIN,$in,1000000);
 	$time = now();
 	$delta = $time - $last_time;
 	print $fh pack("L*",$delta,length $in),$in;
-	print STDOUT $in;
+	if(not $save_to_stdout) { print STDOUT $in; }
 	$last_time = $time;
 	if(not $read) {
 	    # Select says there is something to read,
@@ -162,17 +217,39 @@ sub min(@) {
 }
 
 sub readfile {
+    # Input is in .tt-format
     my $file = shift;
-    open(my $fh, "<", $file) || die;
+    my $fh;
+    if($file eq "-") {
+	$fh = *STDIN;
+    } else {
+	open($fh, "<", $file) || die;
+    }
+    my $fileformat;
+    if(sysread($fh,$fileformat,4)) {
+	if($fileformat eq "TTM1") {
+	    read_ttm1($fh);
+	} else {
+	    error("Unsupported file format: $fileformat");
+	}
+    }
+}
+
+sub read_ttm1 {
+    my $fh = shift;
+    my $in;
+    my $nread;
     while(1) {
-	my $in;
-	if(sysread($fh,$in,8)) {
+	if($nread = sysread($fh,$in,8)) {
+	    if($nread != 8) { die; }
 	    # time in ms, length in bytes
 	    my ($delta,$length) = unpack("L*",$in);
 	    $delta = min($delta/$opt::factor,$opt::maxwait*1000);
 	    select(undef,undef,undef,$delta/1000);
-	    sysread($fh,$in,$length);	
-	    print $in;
+	    while($nread = sysread($fh,$in,$length)) {
+		$length -= $nread;
+		print $in;
+	    }
 	} else {
 	    # Blocking sysread says there is something read,
 	    # but there is not => eof
@@ -206,7 +283,7 @@ sub help() {
 	 "teetime [-m max] [-f factor] -i file",
 	 "",
 	 "-a  append to file",
-	 "-f  playback speed",
+	 "-f  playback speed factor",
 	 "-i  read from file",
 	 "-m  max wait seconds",
 	 "",
@@ -214,6 +291,19 @@ sub help() {
 	 "",);
 }
 
+sub error(@) {
+    my @w = @_;
+    my $prog = $Global::progname || "teetime";
+    status(map { ($prog.": Error: ". $_); } @w);
+}
+
+sub status(@) {
+    my @w = @_;
+    my $fh = *STDERR;
+    print $fh map { ($_, "\n") } @w;
+    flush $fh;
+}
+
 sub debug {
     $opt::D or return;
     @_ = grep { defined $_ ? $_ : "" } @_;
@@ -252,5 +342,3 @@ if(GetOptions("debug|D=s" => \$opt::D,
     help();
     exit(1);
 }
-    
-