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63 lines
2.2 KiB
Plaintext
63 lines
2.2 KiB
Plaintext
* ffmpeg can use YUV files as input :
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ffmpeg /tmp/out.mpg /tmp/test
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If will use the files:
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/tmp/test0.Y, /tmp/test0.U, /tmp/test0.V,
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/tmp/test1.Y, /tmp/test1.U, /tmp/test1.V, etc...
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The Y files use twice the resolution of the U and V files. They are
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raw files, without header. They can be generated by all decent video
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decoders.
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* ffmpeg can use a video4linux compatible video source :
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ffmpeg /tmp/out.mpg
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Note that you must activate the right video source and channel
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before launching ffmpeg. You can use any TV viewer such as xawtv by
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Gerd Knorr which I find very good.
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* There are some importants options to know:
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-s size set frame size [160x128]
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-f format set encoding format [mpeg1]
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-r fps set frame rate [25]
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-b bitrate set the bitrate in kbit/s [100]
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-t time set recording time in seconds [10.0]
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The frame size can also be: cif, qcif, sqcif and 4cif.
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The encoding format can be mpeg1, h263 or rv10.
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Advanced options are:
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-d device set video4linux device name
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-g gop_size set the group of picture size.
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An 'intra' frame is generated every gop_size frames.
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-i use only intra images (speed up compression, but lower quality).
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-c comment set the comment string.
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Comment strings are only used for Real Video(tm) encoding. Tags are
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used in the comment string. A typical comment string is:
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"+title=Test Video +author=FFMpeg +copyright=Free +comment=Generated by FFMpeg 1.0"
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The output file can be "-" to output to a pipe. This is only possible
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with mpeg1 and h263 formats.
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* Tips:
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- For low bit rate application, use a low frame rate and a small gop
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size. This is especially true for real video where the Linux player
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does not seem to be very fast, so it can miss frames. An example is:
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ffmpeg -g 3 -r 3 -t 10 -b 50 -s qcif -f rv10 /tmp/b.rm
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- The parameter 'q' which is displayed while encoding is the current
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quantizer. The value of 1 indicates that a very good quality could
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be achieved. The value of 31 indicates the worst quality. If q=31
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too often, it means that the encoder cannot compress enough to meet
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your bit rate. You must either increase the bit rate, decrease the
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frame rate or decrease the frame size.
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