THFFmpeg

Some (quick and not so dirty) bindings of ffmpeg for torch. Big thanks to https://github.com/mpenkov/ffmpeg-tutorial for their tutorials.

Under BSD License.

Install

It requires ffmpeg 2.x (tested with 2.8.5) for now.

Clone this git, then type

luarocks make

Troubleshooting

When installing, I had a problem with the version of ffmpeg (the headers version didn't match the loaded library). There is now a check at initialization. If it fails, make sure that you compile with the same headers. A way to force them is

luarocks make
cd build
ccmake .
# set the correct paths
cd ..
luarocks make

After that, as long as you don't remove the build folder, it should compile fine with the future luarocks make calls.

The only way I found to set the correct paths were to add -I/usr/include/ffmpeg to the CXX and C flags, in ccmake .. This should work on NYU servers, but other paths may be necessary depending on where you installed ffmpeg.

Testing

To test the install, you can run

th test/test.th

Usage

In torch:

require 'thffmpeg'

decoder = THFFmpeg() --creates a decoder object
decoder:open('myvideo.avi') --opens the video myvideo.avi
frame1 = decoder:next_frame() --allocates a new tensor and puts the first frame in it
frame2 = torch.Tensor(42,42)
decoder:next_frame(frame2) --resizes frame2 if necessary and puts the second frame in it
decoder:close() --closes the video
decoder:open('myvideo2.avi') --opens the video myvideo2.avi

THFFmpeg:open(filename)

Opens a video file. If another was opened in the same THFFmpeg object, it is closed. It sets the variables h and w of the THFFmpeg object to the size of the video stream.

THFFmpeg:close()

Closes a video file. It is not usually strictly necessary, as the decoder will automatically close the opened video when another video is opened, or when the decoder is garbage collected.

[res] THFFmpeg:next_frame([dst])

Decodes and returns the next frame. If dst is provided, it is used as a destination buffer, and must have the correct size. This function returns nil when there is no more frames to read.

[res] THFFmpeg:skip_frame()

Skips a frame. Returns true if successful and false otherwise. Because the frame is not processed, it is faster than next_frame.

[res] THFFmpeg:seek(idx)

Seeks the idx-th frame. Because of limitations of video format, this function decodes every frame from the beginning, so it might be slow on large videos. However, it will always be faster than calling idx times the function next_frame because the images are not processed. This function returns true if the seek was a success, and false otherwise.

[res] THFFmpeg:length()

Returns the length of the video. As for seek, this function decodes all frames of the video and therefore might be slow on large videos.