Installing ffmpeg with libx264
- 1. Make sure
libx264-devs or x264-libs is installed in your system
- 2. Always install ffmpeg from a repo such that it is compiled with
--enable-libx264 or compile it yourself with --enable-libx264 enabled
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Using ffmpeg with libx264 and native aac
- 1.
-c:v libx264: Encodes with X.264 codec
- I.
-preset: Determines encoding speed to compression ratio. ultrafast, superfast, veryfast, faster, fast, medium, slow, slower, veryslow, placebo. medium is default. placebo is not useful at all.
- II.
-crf: Constant Rate Factor. Determines output quality. 0 is lossless, 23 is default, and 51(8-bit x264) or 63(10-bit x264) is worst possible. Increasing the CRF value +6 is roughly half the bitrate while -6 is roughly twice the bitrate. A typical example:
ffmpeg -i input -c:v libx264 -preset slow -crf 22 -c:a copy output.mkv
- III.
-qp 0: Lossless. For fastest encoding:
ffmpeg -i input -c:v libx264 -preset ultrafast -qp 0 output.mkv
and for best compression:
ffmpeg -i input -c:v libx264 -preset veryslow -qp 0 output.mkv
[Most non-FFmpeg based players will not be able to decode lossless.]
- IV. two pass: Targets a specfic size. Target Size (kB) * 8 / Video Time (seconds) = total bitrate (kbps). total bitrate (kbps) - target audio bitrate (kbps) = target video bitrate (kbps). Example:
ffmpeg -y -i input -c:v libx264 -preset medium -b:v 555k -pass 1 -c:a libfdk_aac -b:a 128k -f mp4 /dev/null && \
ffmpeg -i input -c:v libx264 -preset medium -b:v 555k -pass 2 -c:a libfdk_aac -b:a 128k output.mp4
- 2.
-c:a aac: Encodes with Native ffmpeg AAC codec. As it is experimental -strict -2 should be used.
- I.
-b:a: Constant Bit Rate. Example:
ffmpeg -i input.wav -strict -2 -c:a aac -b:a 240k output.m4a
- II.
-q:a: Audio Quality (0.1-10). Example:
ffmpeg -i input.wav -strict -2 -c:a aac -q:a 6 output.m4a
- Note: You can use
libx265 with the same options as libx264 to encode in experimental X.265 codec. Here the default CRF of 28 corresponds to CRF of 23 in X.264.
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To remove or drop an audio or a video stream use -an or -vn respectively.
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Joining or concatenating files
- 1.
concat filter: Concatenates files with different codecs
- I. Example:
ffmpeg \
-i input1.mp4 \
-i input2.webm \
-filter_complex '[0:0] [0:1] [1:0] [1:1] concat=n=2:v=1:a=1 [v] [a]' \
-map '[v]' -map '[a]' \
-c:v libx264 -preset slow -crf 22 \
output.mkv
- II. In
[0:0] [0:1] etc. the first number represents the input file number and the second number represents the stream number (usually 0 for video and 1 for audio). All desired streams are mentioned here.
- III. The name of the filter is
concat, number of input files is n=2, number of output video streams is v=1, number of output audio streams is a=1, names of the output streams are [v] and [a].
- IV.
-map '[v]' -map '[a]' tells ffmpeg to use the result of the filter rather than the streams themselves from input files for further operations.
- V. As filters are incompatible with stream copying, you can't use
-c copy in this method.
- 2.
concat protocol: Concatenates certain file formats with same codecs. Works at file level rather than stream level.
- I. Example:
ffmpeg -i 'concat:input1.mpg|input2.mpg|input3.mpg' -c copy output.mpg
- II. mp4 files can be losslessly concatenated. Example:
ffmpeg -i input1.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate1.ts
ffmpeg -i input2.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts intermediate2.ts
ffmpeg -i 'concat:intermediate1.ts|intermediate2.ts' -c copy -bsf:a aac_adtstoasc output.mp4
- III. Same as II using named pipes. Example:
mkfifo temp1 temp2
ffmpeg -i input1.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts temp1 2> /dev/null & \
ffmpeg -i input2.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts temp2 2> /dev/null & \
ffmpeg -f mpegts -i 'concat:temp1|temp2' -c copy -bsf:a aac_adtstoasc output.mp4
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Cutting files
- 1.
-ss and -to: Using start and end position
- I. Example:
ffmpeg -i input.mp4 -ss 00:00:03.000 -to 00:00:11.000 -c copy cut.mp4
or
ffmpeg -i input.mp4 -ss 3 -to 11 -c copy cut.mp4
- II. Cuts without Reencoding movies from 3 second to 11 second.
- III. Time format is either in seconds or in 'hh:mm:ss[.xxx]'
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Merging a video and an audio streams into a file
- 1.
-map: Mapping input and output streams
- I. Example:
ffmpeg -i video.mp4 -i audio.wav \
-c:v libx264 -preset slow -crf 22 -c:a aac -strict experimental \
-map 0:v:0 -map 1:a:0 output.mp4
- II. Maps video stream from the first file and audio stream from the second file as output streams.
- III. The order of
-map options, specified on cmd line, will create the same order of streams in the output file.
- IV. More than two streams can be merged into a single file.
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Changing speed of a video
- 1.
setpts filter: Change speed of a video
- I. the audio stream is not changed, so it should ideally be disabled with
-an.
- II. Example:
ffmpeg -i input.mp4 -filter:v 'setpts=0.5*PTS' output.mp4
or
ffmpeg -i input.mp4 -filter:v 'setpts=2.0*PTS' output.mp4
- III. Doubles or halves the speed of the video respectively.
- IV. Example:
ffmpeg -i input.mp4 -r 16 -filter:v 'setpts=0.25*PTS' output.mp4
- V. Quadruples the speed of the video and avoids framedrop (framerate at input = 4 to framerate at output = 16).
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Scaling or resizing a video
- 1.
scale filter: Resize a video
- I. Example:
ffmpeg -i input.avi -vf scale=320:240 output.avi
or
ffmpeg -i input.jpg -vf scale=320:240 output_320x240.png
- II. Resizes a video or an image to a specific size (here 320x240).
- III. Example:
ffmpeg -i input.jpg -vf scale=320:-1 output_320.png
or
ffmpeg -i input.jpg -vf scale=-1:240 output_240.png
- IV. Resizes and keeps the aspect ratio same as original.
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