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y4mtoppm - Convert YUV4MPEG2 stream to PPM images


y4mtoppm [options]


y4mtoppm converts a YUV4MPEG2 stream into a sequence of raw PPM images.

Output is to stdout (but feel free to have the shell redirect to a file).

Input is read from stdin, like all other YUV4MPEG2 filters and tools. YUV4MPEG2 streams
contain frames using the Y'CbCr colorspace (ITU-R BT.601). y4mtoppm will convert each
pixel to the usual R'G'B' colorspace used for computer graphics.

YUV4MPEG2 streams may (often!) have subsampled chroma planes. y4mtoppm can upsample
"4:2:0 JPEG" streams using a simple, lousy algorithm. Better results will be obtained
using a filters such as y4mscaler(1) which are capable of general-purpose subsampling
operations. y4mtoppm will fail on streams which have chroma subsampling modes other than
4:4:4 or 4:2:0-JPEG.

For interlaced streams, these operations are performed on each field individually. Fields
can be output as separate PPM images in time-order (default), or interleaved into full-
frame images.

If multiple PPM images are generated, they are simply output one after another. If you
want to turn such a "multi-image" PPM stream/file into individual files, use pnmsplit.
(Some PNM filters can process multi-image files/streams; however, many written before June
2000 will only process the first image.)

y4mtoppm and ppmtoy4m are inverses of each other; you can pipe the output of one into the
other, and vice-versa. Note that the colorspace (and subsampling) operations are lossy in
both directions. And, when converting to PPM, information on interlacing and sample
aspect ratio is lost (but can be reconstructed by supplying command-line arguments to


y4mtoppm accepts the following options:

-L For interlaced streams, output a single PPM image for each frame, containing two
interleaved fields. (Otherwise, two PPM images will be generated for each frame; one
per field.)

-v [0,1,2]
Set verbosity level.
0 = warnings and errors only.
1 = add informative messages, too.
2 = add chatty debugging message, too.


To turn the first 15 frames of an (MJPEG or DV) AVI file into individual PPM files:

lav2yuv -f 15 your-video.avi | y4mtoppm | pnmsplit - "your-video-%d.ppm"

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