Does the encoding parameter within the ROS driver use the onboard hardware?

fsarfraz

Hello,

I am trying to figure out whether or not this parameter for the ROS depthai driver performs video encoding similar to the Encoder Node from depthai - i_low_bandwidth_ffmpeg_encoder: libx264

My understanding is that this ffmpeg encoder is being processed on the host machine CPU rather than on the OAK Device. Can somebody confirm or tell me otherwise?

If it does encode on the device - is there a way to access the output bitstream while still utilizing the ROS driver?

Thank you,

jakaskerl

fsarfraz cc @Luxonis-Adam

Luxonis-Adam

Hi, this parameter is set if you want to publish ROS FFMPEG messages and it is passed to the topic name so that FFMPEG message subscribers can decode those messages further.

fsarfraz

Luxonis-Adam -- Does that mean the ROS FFPMEG message is being filled out with encoded H264 data? If so, is my OAK D pro encoding it to H264 if the parameter is set to "libx264"? And what other values can I use other than "libx264" for this parameter?

I really appreciate the response-- hope its not too many questions.

Thank you,

Luxonis-Adam

Hi, it works as follows:

If i_low_bandwidth parameter is set to true, VideoEncoder DAI node is create automatically created for passing the messages between the devices and host.
By default, i_publish_compressed parameter is set to false, which results in message conversion from DAI encoded frames to ROS Image messages. Note this is only currently only available if encoder profile is set to MJPEG (default)
When i_publish_compressed is set to true, instead of converting DAI Encoded frames to ROS Image messages they are converted to CompressedImage (in case of MJPEG) and FFMPEGMsg (in case of H264 message), which avoid decoding the messages but prevents using ImageTransport for message publishing. For handling those messages you would need to refer to respective ROS packages.

Regarding libx264 - I don't think this parameter matters as much here as it is just passed along with the message and might be used by subscribers down the line. For device encoding customization, you can experiment with following parameters:

    i_low_bandiwdth_frame_freq: 30
    i_low_bandwidth_bitrate: 0
    i_low_bandwidth_profile: 4
    i_low_bandwidth_quality: 50