>I have an MJPEG AVI that I wish to split into a series of JPEGs.
>I've tried using lavtran, like so:
>
>bash% lavtrans +n -o image%05d.jpeg -f i vid.AVI
>
>but it generates JPEGS with empty huffman tables (0x0 DHT).
Beware that the JPEG's in an MJPEG stream (thus, those dumped out
by lavtrans) are in a slightly different colorspace than the
ones you want for plain old still images. (E.g. black is at
Y'=16, and white is Y'=235; chroma is similarly compressed.)
>So the approach I end up using is to first translate the MJPEG to
>a YUV stream, transform these to PNMs, then transform the PNMs to
>JPEGs:
>
>bash% lav2yuv +n MVI_1704.AVI | y4mtoppm | pnmsplit - image%d.pnm
>
>Is there a cleaner way? A way of using mjpegtools to go directly
>from MJPEG to JPEGs (and filling out DHTs) ?
This is about as clean as it gets if you want the correct colorspace.
Fixing up the colorspace requires at a minimum:
1) decompress to Y'CbCr
2) convert video Y'CbCr to graphics Y'CbCr
3) recompress to JPEG
The pipeline you have above replaces (2) with:
2.0) convert video Y'CbCr to R'G'B'
2.1) convert R'G'B' to graphics Y'CbCr
I imagine the decompress/recompress cycle is the biggest source of loss.
-m
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