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====== ffmpeg ======

===== basic usage =====

Use output file as last argument.

<code>
ffmpeg output.mp4
</code>

File format (and its defaults) are derived from file ending.

Use -i to specify input files.

<code>
ffmpeg -i film.mp4 -i subtitles.srt
</code>

Several input files are possible.

Use -map to select streams.

<code>
ffmpeg -i film.mp4 -i subtitles.srt -map 0:0 -map 0:2 -map 1:0
</code>

i:j means take stream with index j in file with index i. File indices are given by order of -i uses in the command line.

Specify output codecs and options.

<code>
-c:v copy
-c:v mpeg4 -b:v 8000k
-c:v libx264 -crf 17 (lower numbers = higher quality)
-c:a copy
-c:a libmp3lame -b:a 320k
-c:a libfdk_aac -b:a 384k
-c:a aac -b:a 384k
-c:s mov_text
</code>

====== useful options ======

===== cutting off borders =====

centred:

<code>
-vf crop=in_w-20:in_h-100
</code>

positioned:

<code>
-vf crop=in_w-20:in_h-100:20:100
</code>

means cut off 10px off top, 10px off bottom, 50px off left, 50px off right.

===== starting and ending at a specific position =====

<code>
-ss 00:03:40 -t 00:01:12
</code>

or

<code>
-ss 220 -t 72
</code>

numbers in seconds (float)

===== concatenate same-codec files =====

Create file containing file names, e.g.:

<code>
file 'file1.mp4'
file 'file2.mp4'
</code>

Then:

<code>
ffmpeg -f concat -safe 0 -i .files -c copy output.mp4
</code>

===== extract d frames per second =====

<code>
ffmpeg -i input.mp4 -q:v 2 -r d output-%03d.png
</code>

Prefer png for higher quality (does not need -q:v).

To extract only key frames:

<code>
ffmpeg -skip_frame nokey -i input.mp4 -q:v 2 -r d output-%03d.png
</code>

===== remove metadata =====

<code>
-map_metadata -1
</code>

===== dump metadata =====

<code>
ffmpeg -i input.mp3 -f ffmetadata metadata.txt
</code>