wcap: Just make wcap-decode dump YUV4MPEG2

Instead of having a custom fork of the vpxenc tool in weston, we can
just dump raw YUV data in the YUV4MPEG2 format and feed that into the
upstream vpxenc.  This also works with theora_encoder and probably many
other encoders.

wcap/README

@@ -9,18 +9,18 @@ something actually changes.
 Recording in Weston is started by pressing MOD+R and stopped by
 pressing MOD+R again.  Currently this leaves a capture.wcap file in
 the cwd of the weston process.  The file format is documented below
-and Weston comes with two tools to convert the wcap file into
-something more usable:
+and Weston comes with the wcap-decode tool to convert the wcap file
+into something more usable:
 
- - wcap-snapshot; a simple tool that will extract a given frame from
-   the capture as a png.  This will produce a lossless screenshot,
-   which is useful if you're trying to screenshot a brief glitch or
-   something like that that's hard to capture with the screenshot tool.
+ - Extract single or all frames as individual png files.  This will
+   produce a lossless screenshot, which is useful if you're trying to
+   screenshot a brief glitch or something like that that's hard to
+   capture with the screenshot tool.
 
-   wcap-snapshot takes a wcap file as its first argument.  Without
-   anything else, it will show the screen size and number of frames in
-   the file.  With an integer second argument, it will extract that
-   frame as a png:
+   wcap-decode takes a number of options and a wcap file as its
+   arguments.  Without anything else, it will show the screen size and
+   number of frames in the file.  Pass --frame=<frame> to extract a
+   single frame or pass --all to extract all frames as png files:
 
 	[krh@minato weston]$ wcap-snapshot capture.wcap 
 	wcap file: size 1024x640, 176 frames
@@ -28,23 +28,23 @@ something more usable:
 	wrote wcap-frame-20.png
 	wcap file: size 1024x640, 176 frames
 
- - wcap-decode; this is a copy of the vpxenc tool from the libvpx
-   repository, with wcap input file support added.  The tool can
-   encode a wcap file into a webm video (http://www.webmproject.org/).
-   The command line arguments are identical to what the vpxenc tool
-   takes and wcap-decode will print them if run without any arguments.
+ - Decode and the wcap file and dump it as a YUV4MPEG2 stream on
+   stdout.  This format is compatible with most video encoders and can
+   be piped directly into a command line encoder such as vpxenc (part
+   of libvpx, encodes to a webm file) or theora_encode (part of
+   libtheora, encodes to a ogg theora file).
 
-   The minimal command line requires a webm output file and a wcap
-   input file:
+   Using vpxenc to encode a webm file would look something like this:
 
-	[krh@minato weston]$ wcap-decode -o foo.webm capture.wcap  
+	[krh@minato weston]$ wcap-decode  --yuv4mpeg2 ../capture.wcap |
+		vpxenc --target-bitrate=1024 --best -t 4 -o foo.webm  -
 
-   but it's possible to select target bitrate and output framerate and
-   it's typically useful to pass -t 4 to let the tool use multiple
-   threads:
+   where we select target bitrate, pass -t 4 to let vpxenc use
+   multiple threads.  To encode to Ogg Theora a command line like this
+   works:
 
-	[krh@minato weston]$ wcap-decode --target-bitrate=1024 \
-		--best -t 4 -o foo.webm capture.wcap  --fps=10/1
+	[krh@minato weston]$ wcap-decode ../capture.wcap  --yuv4mpeg2 |
+		theora_encode - -o cap.ogv
 
 
 WCAP File format