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diff --git a/doc/ffmpeg.txt b/doc/ffmpeg.txt new file mode 100644 index 0000000000..7352a662e2 --- /dev/null +++ b/doc/ffmpeg.txt @@ -0,0 +1,181 @@ +*************** FFMPEG soft VCR documentation ***************** + +0) Introduction +--------------- + + FFmpeg is a very fast video and audio encoder. It can grab from + files or from a live audio/video source. + + The command line interface is designed to be intuitive, in the sense + that ffmpeg tries to figure out all the paramters, when + possible. You have usually to give only the target bitrate you want. + + FFmpeg can also convert from any sample rate to any other, and + resize video on the fly with a high quality polyphase filter. + +1) Video and Audio grabbing +--------------------------- + +* ffmpeg can use a video4linux compatible video source and any Open + Sound System audio source: + + ffmpeg /tmp/out.mpg + + Note that you must activate the right video source and channel + before launching ffmpeg. You can use any TV viewer such as xawtv by + Gerd Knorr which I find very good. You must also set correctly the + audio recording levels with a standard mixer. + +2) Video and Audio file format convertion +----------------------------------------- + +* ffmpeg can use any supported file format and protocol as input : + +examples: + + ffmpeg -i /tmp/test%d.Y /tmp/out.mpg + +If will use the files: +/tmp/test0.Y, /tmp/test0.U, /tmp/test0.V, +/tmp/test1.Y, /tmp/test1.U, /tmp/test1.V, etc... + +The Y files use twice the resolution of the U and V files. They are +raw files, without header. They can be generated by all decent video +decoders. You must specify the size of the image with the '-s' option +if ffmpeg cannot guess it. + +* You can set several input files and output files: + + ffmpeg -i /tmp/a.wav -s 640x480 -i /tmp/a.yuv /tmp/a.mpg + +Convert the audio file a.wav and the raw yuv video file a.yuv to mpeg file a.mpg + +* you can also do audio and video convertions at the same time: + + ffmpeg -i /tmp/a.wav -ar 22050 /tmp/a.mp2 + +Convert the sample rate of a.wav to 22050 Hz and encode it to MPEG audio. + +* you can encode to several formats at the same time and define a + mapping from input stream to output streams: + + ffmpeg -i /tmp/a.wav -ab 64 /tmp/a.mp2 -ab 128 /tmp/b.mp2 -map 0:0 -map 0:0 + + convert a.wav to a.mp2 at 64 kbits and b.mp2 at 128 kbits. '-map + file:index' specify which input stream is used for each output + stream, in the order of the definition of output streams. + +NOTE: to see the supported input formats, use 'ffmpeg -formats'. + +2) Invocation +------------- + +* The generic syntax is : + + ffmpeg [[options][-i input_file]]... {[options] output_file}... + + If no input file is given, audio/video grabbing is done. + + As a general rule, options are applied to the next specified + file. For example, if you give the '-b 64' option, it sets the video + bitrate of the next file. Format option may be needed for raw input + files. + + By default, ffmpeg tries to convert as losslessly as possible: it + uses the same audio and video parameter fors the outputs as the one + specified for the inputs. + +* Main options are: + +-h show help +-formats show available formats, codecs and protocols +-L print the LICENSE +-i filename input file name +-y overwrite output files +-t duration set recording time in seconds +-f format set encoding format [guessed] +-title string set the title +-author string set the author +-copyright string set the copyright +-comment string set the comment + +* Video Options are: + +-s size set frame size [160x128] +-r fps set frame rate [25] +-b bitrate set the video bitrate in kbit/s [200] +-vn disable video recording [no] + +* Audio Options are: + +-ar freq set the audio sampling freq [44100] +-ab bitrate set the audio bitrate in kbit/s [64] +-ac channels set the number of audio channels [1] +-an disable audio recording [no] + +Advanced options are: + +-map file:stream set input stream mapping +-g gop_size set the group of picture size [12] +-intra use only intra frames [no] +-qscale q use fixed video quantiser scale (VBR) +-c comment set the comment string +-vd device set video4linux device name [/dev/video] +-vcodec codec force audio codec +-me method set motion estimation method +-ad device set audio device name [/dev/dsp] +-acodec codec force audio codec + +The output file can be "-" to output to a pipe. This is only possible +with mpeg1 and h263 formats. + +3) Protocols + + ffmpeg handles also many protocols specified with the URL syntax. + + Use 'ffmpeg -formats' to have a list of the supported protocols. + + The protocol 'http:' is currently used only to communicate with + ffserver (see the ffserver documentation). When ffmpeg will be a + video player it will also be used for streaming :-) + +4) File formats and codecs +-------------------------- + + Use 'ffmpeg -formats' to have a list of the supported output + formats. Only some formats are handled as input, but it will improve + in the next versions. + +5) Tips +------- + +- For streaming at very low bit rate application, use a low frame rate + and a small gop size. This is especially true for real video where + the Linux player does not seem to be very fast, so it can miss + frames. An example is: + + ffmpeg -g 3 -r 3 -t 10 -b 50 -s qcif -f rv10 /tmp/b.rm + +- The parameter 'q' which is displayed while encoding is the current + quantizer. The value of 1 indicates that a very good quality could + be achieved. The value of 31 indicates the worst quality. If q=31 + too often, it means that the encoder cannot compress enough to meet + your bit rate. You must either increase the bit rate, decrease the + frame rate or decrease the frame size. + +- If your computer is not fast enough, you can speed up the + compression at the expense of the compression ratio. You can use + '-me zero' to speed up motion estimation, and '-intra' to disable + completly motion estimation (you have only I frames, which means it + is about as good as JPEG compression). + +- To have very low bitrates in audio, reduce the sampling frequency + (down to 22050 kHz for mpeg audio, 22050 or 11025 for ac3). + +- To have a constant quality (but a variable bitrate), use the option + '-qscale n' when 'n' is between 1 (excellent quality) and 31 (worst + quality). + +- When converting video files, you can use the '-sameq' option which + uses in the encoder the same quality factor than in the decoder. It + allows to be almost lossless in encoding. |