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WriteGear API Usage Examples: Compression Mode

Important Information

  • WriteGear MUST requires FFmpeg executables for its Compression capabilities in Compression Mode. Follow these dedicated Installation Instructions ➶ for its installation.

  • In case WriteGear API fails to detect valid FFmpeg executables on your system (even if Compression Mode is enabled), it automatically fallbacks to Non-Compression Mode.

  • DO NOT feed frames with different dimensions or channels to WriteGear, otherwise WriteGear will exit with ValueError.

  • When using the -i FFmpeg parameter in output_params to provide an additional audio or video source, ensure it DOES NOT interfere with WriteGear's internal frame pipeline. Interference can cause the pipeline to break.

  • To ensure WriteGear produces valid output when using an additional stream -i parameter with videos shorter than 60 seconds, use the -disable_force_termination flag.

  • Encoding heavy resolution multimedia files can take up to ~0.2 to 2 seconds. Please wait for the WriteGear API to terminate itself and DO NOT kill the process manually.

  • Always use writer.close() at the very end of the main code. NEVER USE IT INBETWEEN CODE to avoid undesired behavior.

After going through WriteGear Usage Examples, Checkout more bonus examples here ➶

 

Bare-Minimum Usage

Following is the bare-minimum code you need to get started with WriteGear API in Compression Mode:

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# import required libraries
from vidgear.gears import CamGear
from vidgear.gears import WriteGear
import cv2

# open any valid video stream(for e.g `myvideo.avi` file)
stream = CamGear(source="myvideo.avi").start()

# Define writer with default parameters and suitable output filename for e.g. `Output.mp4`
writer = WriteGear(output="Output.mp4")

# loop over
while True:

    # read frames from stream
    frame = stream.read()

    # check for frame if Nonetype
    if frame is None:
        break

    # {do something with the frame here}

    # write frame to writer
    writer.write(frame)

    # Show output window
    cv2.imshow("Output Frame", frame)

    # check for 'q' key if pressed
    key = cv2.waitKey(1) & 0xFF
    if key == ord("q"):
        break

# close output window
cv2.destroyAllWindows()

# safely close video stream
stream.stop()

# safely close writer
writer.close()

 

Using Compression Mode in RGB Mode

In Compression Mode, WriteGear API contains rgb_mode boolean parameter for RGB Mode, which when enabled (i.e. rgb_mode=True), specifies that incoming frames are of RGB format (instead of default BGR format). This mode makes WriteGear directly compatible with libraries that only supports RGB format.

The complete usage example is as follows:

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# import required libraries
from vidgear.gears import VideoGear
from vidgear.gears import WriteGear
import cv2

# Open live video stream on webcam at first index(i.e. 0) device
stream = VideoGear(source=0).start()

# Define writer with default parameters and suitable output filename for e.g. `Output.mp4`
writer = WriteGear(output="Output.mp4")

# loop over
while True:

    # read frames from stream
    frame = stream.read()

    # check for frame if Nonetype
    if frame is None:
        break

    # simulating RGB frame for example
    frame_rgb = frame[:, :, ::-1]

    # writing RGB frame to writer
    writer.write(frame_rgb, rgb_mode=True)  # activate RGB Mode

    # Show output window
    cv2.imshow("Output Frame", frame)

    # check for 'q' key if pressed
    key = cv2.waitKey(1) & 0xFF
    if key == ord("q"):
        break

# close output window
cv2.destroyAllWindows()

# safely close video stream
stream.stop()

# safely close writer
writer.close()

 

Using Compression Mode with controlled FrameRate

WriteGear API provides -input_framerate attribute for its options dictionary parameter in Compression Mode, which allow us to control/set the constant framerate of the output video.

Advanced Tip for setting constant framerate

If -input_framerate attribute doesn't works for you, then define it in conjunction with another -r FFmpeg parameter as attribute:

# set output constant framerate to (say 60 fps)
output_params = {"-input_framerate":60, "-r":60}
# assign that to WriteGear
writer = WriteGear(output="out.mp4", logging =True, **output_params)

But make sure you MUST set value of -r and -input_framerate parameter less than or equal to your input source framerate.

In this code we will retrieve framerate from video stream, and set it as -input_framerate attribute for option parameter in WriteGear API:

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# import required libraries
from vidgear.gears import CamGear
from vidgear.gears import WriteGear
import cv2

# Open live video stream on webcam at first index(i.e. 0) device
stream = CamGear(source=0).start()

# retrieve framerate from CamGear Stream and pass it as `-input_framerate` parameter
output_params = {"-input_framerate": stream.framerate}

# Define writer with defined parameters and suitable output filename for e.g. `Output.mp4`
writer = WriteGear(output="Output.mp4", **output_params)

# loop over
while True:

    # read frames from stream
    frame = stream.read()

    # check for frame if None-type
    if frame is None:
        break

    # {do something with the frame here}

    # write frame to writer
    writer.write(frame)

    # Show output window
    cv2.imshow("Output Frame", frame)

    # check for 'q' key if pressed
    key = cv2.waitKey(1) & 0xFF
    if key == ord("q"):
        break

# close output window
cv2.destroyAllWindows()

# safely close video stream
stream.stop()

# safely close writer
writer.close()

 

Using Compression Mode for live streaming

In Compression Mode, WriteGear also allows URL strings (as output) for live streaming realtime frames with its output parameter.

In this example, we will stream live camera frames directly to Twitch :

For streaming with traditional protocols such as RTSP/RTP, Checkout this WriteGear's Bonus Examples ➶.

YouTube-Live Streaming example code also available in WriteGear's Bonus Examples ➶

This example assume you already have a Twitch Account for publishing video.

Make sure to change Twitch Stream Key with yours in following code before running!

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# import required libraries
from vidgear.gears import CamGear
from vidgear.gears import WriteGear
import cv2

# Open live webcam video stream on first index(i.e. 0) device
stream = CamGear(source=0, logging=True).start()

# define required FFmpeg optimizing parameters for your writer
output_params = {
    "-preset:v": "veryfast",
    "-g": 60,
    "-keyint_min": 60,
    "-sc_threshold": 0,
    "-bufsize": "2500k",
    "-f": "flv",
}

# [WARNING] Change your Twitch Stream Key here:
TWITCH_KEY = "live_XXXXXXXXXX~XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"

# Define writer with defined parameters and
writer = WriteGear(
    output="rtmp://live.twitch.tv/app/{}".format(TWITCH_KEY),
    logging=True,
    **output_params
)

# loop over
while True:

    # read frames from stream
    frame = stream.read()

    # check for frame if Nonetype
    if frame is None:
        break

    # {do something with the frame here}

    # write frame to writer
    writer.write(frame)

    # Show output window
    cv2.imshow("Output Frame", frame)

    # check for 'q' key if pressed
    key = cv2.waitKey(1) & 0xFF
    if key == ord("q"):
        break

# close output window
cv2.destroyAllWindows()

# safely close video stream
stream.stop()

# safely close writer
writer.close()

 

Using Compression Mode with Hardware encoders

By default, WriteGear API uses libx264 encoder for encoding output files in Compression Mode. But you can easily change encoder to your suitable supported encoder by passing -vcodec FFmpeg parameter as an attribute with its output_param dictionary parameter. In addition to this, you can also specify the additional properties/features of your system's GPU easily.

User Discretion Advised

This example is just conveying the idea on how to use FFmpeg's hardware encoders with WriteGear API in Compression mode, which MAY/MAY NOT suit your system. Kindly use suitable parameters based your system hardware settings only.

In this example, we will be using h264_vaapi as our hardware encoder and also optionally be specifying our device hardware's location (i.e. '-vaapi_device':'/dev/dri/renderD128') and other features such as '-vf':'format=nv12,hwupload':

Remember to check VAAPI support

To use h264_vaapi encoder, remember to check if its available and your FFmpeg compiled with VAAPI support. You can easily do this by executing following one-liner command in your terminal, and observing if output contains something similar as follows:

ffmpeg  -hide_banner -encoders | grep vaapi 

 V..... h264_vaapi           H.264/AVC (VAAPI) (codec h264)
 V..... hevc_vaapi           H.265/HEVC (VAAPI) (codec hevc)
 V..... mjpeg_vaapi          MJPEG (VAAPI) (codec mjpeg)
 V..... mpeg2_vaapi          MPEG-2 (VAAPI) (codec mpeg2video)
 V..... vp8_vaapi            VP8 (VAAPI) (codec vp8)

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# import required libraries
from vidgear.gears import CamGear
from vidgear.gears import WriteGear
import cv2

# Open live webcam video stream on first index(i.e. 0) device
stream = CamGear(source=0, logging=True).start()

# define required FFmpeg parameters for your writer
output_params = {
    "-vcodec": "h264_vaapi",
    "-vaapi_device": "/dev/dri/renderD128",
    "-vf": "format=nv12,hwupload",
}

# Define writer with defined parameters and suitable output filename for e.g. `Output.mp4`
writer = WriteGear(output="Output.mp4", **output_params)

# loop over
while True:

    # read frames from stream
    frame = stream.read()

    # check for frame if Nonetype
    if frame is None:
        break

    # {do something with the frame here}

    # write frame to writer
    writer.write(frame)

    # Show output window
    cv2.imshow("Output Frame", frame)

    # check for 'q' key if pressed
    key = cv2.waitKey(1) & 0xFF
    if key == ord("q"):
        break

# close output window
cv2.destroyAllWindows()

# safely close video stream
stream.stop()

# safely close writer
writer.close()

 

Using Compression Mode with OpenCV

You can easily use WriterGear API directly with any Video Processing library(For e.g OpenCV itself) in Compression Mode. The complete usage example is as follows:

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# import required libraries
from vidgear.gears import WriteGear
import cv2

# define suitable (Codec,CRF,preset) FFmpeg parameters for writer
output_params = {"-vcodec": "libx264", "-crf": 0, "-preset": "fast"}

# Open suitable video stream, such as webcam on first index(i.e. 0)
stream = cv2.VideoCapture(0)

# Define writer with defined parameters and suitable output filename for e.g. `Output.mp4`
writer = WriteGear(output="Output.mp4", logging=True, **output_params)

# loop over
while True:

    # read frames from stream
    (grabbed, frame) = stream.read()

    # check for frame if not grabbed
    if not grabbed:
        break

    # {do something with the frame here}
    # lets convert frame to gray for this example
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

    # write gray frame to writer
    writer.write(gray)

    # Show output window
    cv2.imshow("Output Gray Frame", gray)

    # check for 'q' key if pressed
    key = cv2.waitKey(1) & 0xFF
    if key == ord("q"):
        break

# close output window
cv2.destroyAllWindows()

# safely close video stream
stream.release()

# safely close writer
writer.close()

 

Using Compression Mode with Live Audio Input

In Compression Mode, WriteGear API allows us to exploit almost all FFmpeg supported parameters that you can think of in its Compression Mode. Hence, combining audio with live video frames is pretty easy.

In this example code, we will merging the audio from a Audio Device (for e.g. Webcam inbuilt mic) to live frames incoming from the Video Source (for e.g external webcam), and save the output as a compressed video file, all in real time:

Example Assumptions

  • You're running are Linux machine.
  • You already have appropriate audio driver and software installed on your machine.
Identifying and Specifying sound card on different OS platforms

Windows OS users can use the dshow (DirectShow) to list audio input device which is the preferred option for Windows users. You can refer following steps to identify and specify your sound card:

  • [OPTIONAL] Enable sound card(if disabled): First enable your Stereo Mix by opening the "Sound" window and select the "Recording" tab, then right click on the window and select "Show Disabled Devices" to toggle the Stereo Mix device visibility. Follow this post ➶ for more details.

  • Identify Sound Card: Then, You can locate your soundcard using dshow as follows:

    c:\> ffmpeg -list_devices true -f dshow -i dummy
ffmpeg version N-45279-g6b86dd5... --enable-runtime-cpudetect
  libavutil      51. 74.100 / 51. 74.100
  libavcodec     54. 65.100 / 54. 65.100
  libavformat    54. 31.100 / 54. 31.100
  libavdevice    54.  3.100 / 54.  3.100
  libavfilter     3. 19.102 /  3. 19.102
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 16.100 /  0. 16.100
[dshow @ 03ACF580] DirectShow video devices
[dshow @ 03ACF580]  "Integrated Camera"
[dshow @ 03ACF580]  "USB2.0 Camera"
[dshow @ 03ACF580] DirectShow audio devices
[dshow @ 03ACF580]  "Microphone (Realtek High Definition Audio)"
[dshow @ 03ACF580]  "Microphone (USB2.0 Camera)"
dummy: Immediate exit requested

  • Specify Sound Card: Then, you can specify your located soundcard in WriteGear as follows:

    # assign appropriate input audio-source
output_params = {
    "-f": "dshow", # !!! warning: always keep this line above "-i" parameter !!!
    "-i":"audio=Microphone (USB2.0 Camera)",
    "-thread_queue_size": "512",
    "-ac": "2",
    "-acodec": "aac",
    "-ar": "44100",
}

If audio still doesn't work then checkout this troubleshooting guide ➶ or reach us out on Gitter ➶ Community channel

Linux OS users can use the alsa to list input device to capture live audio input such as from a webcam. You can refer following steps to identify and specify your sound card:

  • Identify Sound Card: To get the list of all installed cards on your machine, you can type arecord -l or arecord -L (longer output).

    arecord -l

**** List of CAPTURE Hardware Devices ****
card 0: ICH5 [Intel ICH5], device 0: Intel ICH [Intel ICH5]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: ICH5 [Intel ICH5], device 1: Intel ICH - MIC ADC [Intel ICH5 - MIC ADC]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: ICH5 [Intel ICH5], device 2: Intel ICH - MIC2 ADC [Intel ICH5 - MIC2 ADC]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: ICH5 [Intel ICH5], device 3: Intel ICH - ADC2 [Intel ICH5 - ADC2]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: U0x46d0x809 [USB Device 0x46d:0x809], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

  • Specify Sound Card: Then, you can specify your located soundcard in WriteGear as follows:

    The easiest thing to do is to reference sound card directly, namely "card 0" (Intel ICH5) and "card 1" (Microphone on the USB web cam), as hw:0 or hw:1

    # assign appropriate input audio-source
output_params = {
    "-thread_queue_size": "512",
    "-ac": "2",
    "-ar": "48000",
    "-f": "alsa", # !!! warning: always keep this line above "-i" parameter !!!
    "-i": "hw:1",
}

If audio still doesn't work then reach us out on Gitter ➶ Community channel

MAC OS users can use the avfoundation to list input devices for grabbing audio from integrated iSight cameras as well as cameras connected via USB or FireWire. You can refer following steps to identify and specify your sound card on MacOS/OSX machines:

  • Identify Sound Card: Then, You can locate your soundcard using avfoundation as follows:

    ffmpeg -f avfoundation -list_devices true -i ""
ffmpeg version N-45279-g6b86dd5... --enable-runtime-cpudetect
  libavutil      51. 74.100 / 51. 74.100
  libavcodec     54. 65.100 / 54. 65.100
  libavformat    54. 31.100 / 54. 31.100
  libavdevice    54.  3.100 / 54.  3.100
  libavfilter     3. 19.102 /  3. 19.102
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 16.100 /  0. 16.100
[AVFoundation input device @ 0x7f8e2540ef20] AVFoundation video devices:
[AVFoundation input device @ 0x7f8e2540ef20] [0] FaceTime HD camera (built-in)
[AVFoundation input device @ 0x7f8e2540ef20] [1] Capture screen 0
[AVFoundation input device @ 0x7f8e2540ef20] AVFoundation audio devices:
[AVFoundation input device @ 0x7f8e2540ef20] [0] Blackmagic Audio
[AVFoundation input device @ 0x7f8e2540ef20] [1] Built-in Microphone

  • Specify Sound Card: Then, you can specify your located soundcard in WriteGear as follows:

    # assign appropriate input audio-source
output_params = {
    "-thread_queue_size": "512",
    "-ac": "2",
    "-ar": "48000",
    "-f": "avfoundation", # !!! warning: always keep this line above "-audio_device_index" parameter !!!
    "-audio_device_index": "0",
}

If audio still doesn't work then reach us out on Gitter ➶ Community channel

Make sure this -i audio-source it compatible with provided video-source, otherwise you could encounter multiple errors or no output at all.

You MUST use -input_framerate attribute to set exact value of input framerate when using external audio in Real-time Frames mode, otherwise audio delay will occur in output streams.

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# import required libraries
from vidgear.gears import VideoGear
from vidgear.gears import WriteGear
import cv2

# Open live video stream on webcam at first index(i.e. 0) device
stream = VideoGear(source=0).start()

# change with your webcam soundcard, plus add additional required FFmpeg parameters for your writer
output_params = {
    "-input_framerate": stream.framerate,
    "-thread_queue_size": "512",
    "-ac": "2",
    "-ar": "48000",
    "-f": "alsa", # !!! warning: always keep this line above "-i" parameter !!!
    "-i": "hw:1",
}

# Define writer with defined parameters and suitable output filename for e.g. `Output.mp4
writer = WriteGear(output="Output.mp4", logging=True, **output_params)

# loop over
while True:

    # read frames from stream
    frame = stream.read()

    # check for frame if Nonetype
    if frame is None:
        break

    # {do something with the frame here}

    # write frame to writer
    writer.write(frame)

    # Show output window
    cv2.imshow("Output Frame", frame)

    # check for 'q' key if pressed
    key = cv2.waitKey(1) & 0xFF
    if key == ord("q"):
        break

# close output window
cv2.destroyAllWindows()

# safely close video stream
stream.stop()

# safely close writer
writer.close()