Fri Mar 17, 2023 10:39 pm
Hello all. Since there is understandable confusion around bit rates, I would like to offer some information on how the ATEM ISO recordings are made.
First, the Program recording (ISO on or off), is H.264 variable bit rate with the max set by the streaming quality. So, if the streaming quality is set to Streaming High, the max bit rate will be around 9 Mb/s if the fps is above 30. It will be max at 6 Mb/s if the fps is 30 or below. Each quality menu setting will have two bit rates. As this is variable bit rate by design, complex images will have higher bit rates than simple images like graphics on a background. When you see a low bit rate it is because the image content doesn't require any more for the same level of quality.
Second, all ISO recordings are set fixed at Hyperdeck High. These too are variable. The max will be around 70 Mb/s for complex video. Much lower for simple images. For example, the unused inputs will still have a file but since they are black, the bit rate will be very low making very small files.
Last, if the input video is derived from low bit rate content, the ISO files will generally be similar or lower being additionally compressed. For example, if you are streaming a camera directly to the ATEM HD8 ISO, the stream quality of the camera will be recorded in the ISO for that source. It would not be higher. Or even if you are playing H.264 video from a Hyperdeck into the ATEM ISO, the recoding will likely be lower than the original bit rate of the recording since the video is less complex due to additional compression.
I hope this helps explain the scenarios some users experience. Since NAB is coming up soon, I hope many users will stop by and say hello.
Regards, Gary
Gary Adams
Blackmagic Design