Documentation on input formats and conversion

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Somewhere in the documentation, the exact input formats understood by veejay need be described. Mention that internal storage is yuv422, and give example command lines for conversion into respective formats using e.g. ffmpeg:

mjpeg:
ffmpeg -i input-file -vcodec mjpeg -pix_fmt yuvj422p -acodec pcm_s16le -ar 44100 -ac 2 output-file.avi

raw yuv422 (no audio):
ffmpeg -i out19.mp4 -vcodec rawvideo -pix_fmt yuv422p -acodec none test.avi

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Additional:

There is also some documentation here:
https://github.com/c0ntrol/veejay/blob/master/veejay-current/veejay-server/doc/README.video_formats.txt

outdated, but might still contain usefull information:
https://github.com/c0ntrol/veejay/blob/master/veejay-current/veejay-server/doc/HowtoVideoCodecs.txt
https://github.com/c0ntrol/veejay/blob/master/veejay-current/veejay-server/doc/YCbCr.txt
https://github.com/c0ntrol/veejay/blob/master/veejay-current/veejay-server/doc/README.audio

what should be supported:

• AVI MJPEG, MJPEG-b, LJPEG, DV ( fourcc "mjpg", "mjpb", "dmb1", "jpeg","mjpa","jfif", "png", "mpng", "sp5x", "jpg1", "dvsd", "dv", "dvp" )
• AVI HUFFYUV (fourcc "hfyu")
• veejay-only formats: AVI VJ20, VJ22, MLZO (fourcc "vj20","vj22", "mlzo" )
• Quicktime MJPEG/DV
• Pictures (JPG, BMP, PNG, etc)

source:
https://github.com/c0ntrol/veejay/blob/master/veejay-current/veejay-server/libel/avhelper.c
static struct { const char *name; int id; } _supported_codecs[]

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Internally veejay processes all video data in digital YUV (YCbCR) and supports two pixel ranges:

• 0-255 (YUV JPEG/JFIF)
• 16-235 / 16-240 (YCbCr Rec 601)

The sampling from source is converted to 4:2:2 YUV planar before it is passed to the FX render chain.
During the rendering of the FX chain, the data may be converted to/from RGB (for frei0r plugins) or it may be super sampled to 4:4:4 if an FX or plugin requires this.

This is mostly a relic of the old days now as bandwidth and computing power have substantially increased.

• Many video codecs decode into some YUV flavour
• Many capture devices deliver YUV
• Consumes less memory bandwidth than RGB

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Close, continue under #76