Read/Write video using FFMPEG


We are in the process of (slowly) replacing this plugin with a new one that is based on pyav. It is faster and more flexible than the plugin documented here. Check the pyav plugin's documentation for more information about this plugin.

Backend Library: imageio/imageio-ffmpeg


To use this plugin you have to install its backend:

pip install imageio[ffmpeg]

The ffmpeg format provides reading and writing for a wide range of movie formats such as .avi, .mpeg, .mp4, etc. as well as the ability to read streams from webcams and USB cameras. It is based on ffmpeg and is inspired by/based moviepy by Zulko.

Parameters for reading#


The number of frames per second of the input stream. Default None (i.e. read at the file’s native fps). One can use this for files with a variable fps, or in cases where imageio is unable to correctly detect the fps. In case of trouble opening camera streams, it may help to set an explicit fps value matching a framerate supported by the camera.


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.

sizestr | 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.

dtypestr | type

The dtype for the output arrays. Determines the bit-depth that is requested from ffmpeg. Supported dtypes: uint8, uint16. Default: uint8.


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.


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’]


List additional arguments to ffmpeg for output file options (i.e. the stream being read by imageio).


Print information about the video file as reported by ffmpeg.

Parameters for writing#


The number of frames per second. Default 10.


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

qualityfloat | 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.

bitrateint | 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 specifying a fixed bitrate with this parameter.

pixelformat: str

The output video pixel format. Default is ‘yuv420p’ which most widely supported by video players.


List additional arguments to ffmpeg for input file options (i.e. the stream that imageio provides).


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

audio_pathstr | None

Audio path of any audio that needs to be written. Defaults to nothing, so no audio will be written. Please note, when writing shorter video than the original, ffmpeg will not truncate the audio track; it will maintain its original length and be longer than the video.

audio_codecstr | None

The audio codec to use. Defaults to nothing, but if an audio_path has been provided ffmpeg will attempt to set a default codec.


If you are using anaconda and anaconda/ffmpeg you will not be able to encode/decode H.264 (likely due to licensing concerns). If you need this format on anaconda install conda-forge/ffmpeg instead.

You can use the IMAGEIO_FFMPEG_EXE environment variable to force using a specific ffmpeg executable.

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).