FFMPEG Many video formats and cameras (via ffmpeg)¶
Extensions: .mov
, .avi
, .mpg
, .mpeg
, .mp4
, .mkv
, .wmv
The ffmpeg format provides reading and writing for a wide range of movie formats such as .avi, .mpeg, .mp4, etc. And also to read streams from webcams and USB cameras.
To read from camera streams, supply “<video0>” as the filename, where the “0” can be replaced with any index of cameras known to the system.
To use this plugin, the imageio-ffmpeg
library should be installed
(e.g. via pip). For most platforms this includes the ffmpeg executable.
One can use the IMAGEIO_FFMPEG_EXE
environment variable to force
using a specific ffmpeg executable.
When reading from a video, the number of available frames is hard/expensive
to calculate, which is why its set to inf by default, indicating
“stream mode”. To get the number of frames before having read them all,
you can use the reader.count_frames()
method (the reader will then use
imageio_ffmpeg.count_frames_and_secs()
to get the exact number of
frames, note that this operation can take a few seconds on large files).
Alternatively, the number of frames can be estimated from the fps and
duration in the meta data (though these values themselves are not always
present/reliable).
Parameters for reading¶
- fps : scalar
- The number of frames per second to read the data at. Default None (i.e. read at the file’s own fps). One can use this for files with a variable fps, or in cases where imageio is unable to correctly detect the fps.
- loop : bool
- If True, the video will rewind as soon as a frame is requested
beyond the last frame. Otherwise, IndexError is raised. Default False.
Setting this to True will internally call
count_frames()
, and set the reader’s length to that value instead of inf. - size : str | tuple
- The frame size (i.e. resolution) to read the images, e.g. (100, 100) or “640x480”. For camera streams, this allows setting the capture resolution. For normal video data, ffmpeg will rescale the data.
- dtype : str | type
- The dtype for the output arrays. Determines the bit-depth that is requested from ffmpeg. Supported dtypes: uint8, uint16. Default: uint8.
- pixelformat : str
- The pixel format for the camera to use (e.g. “yuyv422” or “gray”). The camera needs to support the format in order for this to take effect. Note that the images produced by this reader are always RGB.
- input_params : list
- List additional arguments to ffmpeg for input file options.
(Can also be provided as
ffmpeg_params
for backwards compatibility) Example ffmpeg arguments to use aggressive error handling: [‘-err_detect’, ‘aggressive’] - output_params : list
- List additional arguments to ffmpeg for output file options (i.e. the stream being read by imageio).
- print_info : bool
- Print information about the video file as reported by ffmpeg.
Parameters for saving¶
- fps : scalar
- The number of frames per second. Default 10.
- codec : str
- the video codec to use. Default ‘libx264’, which represents the widely available mpeg4. Except when saving .wmv files, then the defaults is ‘msmpeg4’ which is more commonly supported for windows
- quality : float | None
- Video output quality. Default is 5. Uses variable bit rate. Highest quality is 10, lowest is 0. Set to None to prevent variable bitrate flags to FFMPEG so you can manually specify them using output_params instead. Specifying a fixed bitrate using ‘bitrate’ disables this parameter.
- bitrate : int | None
- Set a constant bitrate for the video encoding. Default is None causing ‘quality’ parameter to be used instead. Better quality videos with smaller file sizes will result from using the ‘quality’ variable bitrate parameter rather than specifiying a fixed bitrate with this parameter.
- pixelformat: str
- The output video pixel format. Default is ‘yuv420p’ which most widely supported by video players.
- input_params : list
- List additional arguments to ffmpeg for input file options (i.e. the stream that imageio provides).
- output_params : list
- List additional arguments to ffmpeg for output file options.
(Can also be provided as
ffmpeg_params
for backwards compatibility) Example ffmpeg arguments to use only intra frames and set aspect ratio: [‘-intra’, ‘-aspect’, ‘16:9’] - ffmpeg_log_level: str
- Sets ffmpeg output log level. Default is “warning”. Values can be “quiet”, “panic”, “fatal”, “error”, “warning”, “info” “verbose”, or “debug”. Also prints the FFMPEG command being used by imageio if “info”, “verbose”, or “debug”.
- macro_block_size: int
- Size constraint for video. Width and height, must be divisible by this number. If not divisible by this number imageio will tell ffmpeg to scale the image up to the next closest size divisible by this number. Most codecs are compatible with a macroblock size of 16 (default), some can go smaller (4, 8). To disable this automatic feature set it to None or 1, however be warned many players can’t decode videos that are odd in size and some codecs will produce poor results or fail. See https://en.wikipedia.org/wiki/Macroblock.