SYNCHRONIZATION OF AUDIO WITH VIDEO
Today the theme is about: Synchronization of audio with video, something that might seem very complicated to solve at first glance, but which is quite simple when using the right equipment…
Audio to video sync (AV sync, also known as lip sync, or for lack of it: lip sync error), refers to the relative timing of the audio (sound) and video (picture) parts during creation, processing post-production, transmission, reception and reproduction. AV sync can be a problem you encounter on television, video conferences, or movies.
What is lip sync error?
In industry terminology, lip sync error is expressed as: a given time that the audio moves away from perfect sync with the video, where a positive amount of time indicates that the audio is ahead of the video and an amount of time negative indicates that the audio is lagging behind the video. This terminology and indication of lip sync time amount error is used in the professional broadcast industry.
Video feeds, digital or analog audio, or video files often contain some sort of synchronization mechanism, either in the form of interleaved video and audio data or by time code. Data processing must respect the relative timing of the data, eg stretching between or interpolating received data. If processing is not respected, AV sync error will increase whenever data is lost due to transmission errors or due to missing or incorrect processing.
There are different ways in which AV sync can be incorrectly synced:
• During production, AV sync errors happen due to:
– Internal AV sync error: Different signal processing delays between image and sound. In video cameras and in the built-in microphone. AV sync delay is normally corrected automatically, but there are other constraints.
– External AV Sync Error: If a microphone is placed far from the sound source, the audio will be out of sync because the speed of sound is much slower than the speed of light. If the sound source is 340 meters from the microphone, the sound arrives approximately 1 second after the light. AV sync delay increases with distance. When mixing video clips, usually the audio or video needs to be delayed in order to be synchronized perfectly. AV sync delay is static but may vary. Video Editing Effects.
Examples of transmission, reception and playback that can desync the AV:
– A video camera with a built-in microphone will certainly have a sync correction system. A camcorder has an included AV sync type placed in the video and audio feeds. A solid state video camera (for example, a CCD camera and CMOS image sensors) can delay the video signal by one or more frames.
– An AV feed can be corrupted during transmission due to electrical (Cable) failures or interruptions even in wireless transmission – this can cause it to get out of sync. AV sync delay usually increases with time.
– In a production there is extensive use of audio and video signal processing circuits with significant (and often not constant) delays in television systems. There is a specific video signal processing circuit that is widely used and contributes to significant video delays, these should include frame synchronizers, digital video effects processors, video noise reduction, format converters and compression systems.
– The processing circuit may delay the video feed. Processed video requires format conversion and processing, which can add one or more frames of delay to the video.
– Viewing and listening equipment may have different playback times.
– When we handle our feeds on our Broadcast equipment, the audio and video have different paths, what we call immersed audio and video, because they are processed in different paths so their delay time is different.
We were very used to using analog processes, where the delay was less; today and more and more, processes are in greater number and all digital, which creates a greater delay in our image compared to audio processes.
Today, the integration of Broadcast equipment is very important, a good integration is increasingly needed by those who are qualified, in order to correct this type of errors that are increasingly frequent…
How to solve lip desynchronization?
Today there are many tools that help us in this process and that are at our disposal; it is not enough to buy the equipment we consider important for production and connect them, now, in addition to connecting them, it is necessary to put the equipment to communicate with each other, in order to correct errors such as the one we have addressed.
Today our feed does not end up in our hands, most of the time it is sent to signal distributors who sell our signal to the final consumer, and this also intervenes in our Feed, hence the importance of monitoring the arrival of our feed to the our target audience and we intervene in the correction, whenever necessary, to defend our image. A misspelled feed can lead to low ratings and significant losses in the target audience, which can result in financial and objective losses.