Hey Zoom Devs!
I wanted to write up a post to detail how file sizes are affected by our the recording setting to Record a separate audio file of each participant
First, a bit about this setting. You can find it under the Account or User settings page under the Recording tab:
When enabled, separate audio-only files will be created for each participant during a recording. Further documentation on enabling this setting is here.
If we then record a meeting with multiple participants we’ll be able to download all the files using the Get Meeting Recordings API or through the Zoom Web Portal. If you’re using local recording they’ll already be on your system.
If we look at the sizes of all the files we start to notice they are all the same. This is strange because I know that the participant only said ‘goodbye’ at the end of the meeting.
Why is the recording that has all the meeting audio the same size as the nearly empty recording?
If we open up the audio files in a program like Audacity we can start to see what’s happening here:
While the full recording and
separate1 contains significantly more usable audio data than
separate2 all the files have the same duration and use a Constant Bitrate Encoding:
With CBR encoding the bit rate and size of the encoded stream are known prior to encoding. For example, if you are encoding a three minute song at 32,000 bits per second, you know that the file size will be about 704 kilobytes (32,000 bps x 180 seconds / 8 bits per byte / 1,024
What this means is that given the same duration and bitrate of a file, the sizes will be equivalent because the same bitrate is used even during silent portions of the audio track.
When transcribing a meeting, Zoom uses the same process regardless of this setting. This is because Zoom already has separate audio streams to process. For this reason, you won’t see a change to transcription files when this setting is enabled.
I hope that helps you in your Zoom Developer journey! Please comment with any questions you might have.