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## Additional notes
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### Audio/Clip Basics
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### Clip Basics:
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In the simple case (phone/camera recording), video clips have one stereo audio track. There are many more options however.
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Technically, clips (video+audio like .mp4, or audio only like .wav) are primarily **containers** which contain encoded audio/video streams. The container describes what streams there are and in which format (and more). **Streams** can again contain channels. **Channels** represent a single (mono) waveform.
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(Streams are usually called tracks in video editing.)
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![image](uploads/79a760ee671fa9061b110d254996315a/image.png)
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A video clip could now contain a video stream and two audio streams, one with stereo English language (i.e. 2 channels) and one with 5.1 Italian language (i.e. 6 channels). An audio clip from a field recording (with a multi-channel recorder) could contain 5 channels where CH1/CH2 are a stereo voice recording, CH3 is a sound effect mono channel, and CH4/CH5 are used for stereo environment recording. The channels can be combined in an arbitrary way in the input clip, but for editing they are used separately, for example the two voice channels only would be used on an audio track in the timeline.
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To give two examples:
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* A video clip could now contain a video stream and two audio streams, one with stereo English language (i.e. 2 channels) and one with 5.1 Italian language (i.e. 6 channels).
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* An audio clip from a field recording (with a multi-channel recorder) could contain 5 channels where CH1/CH2 are a stereo voice recording, CH3 is a sound effect mono channel, and CH4/CH5 are used for stereo environment recording.
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The channels can be combined in an arbitrary way in the input clip, but for editing they are used separately, for example the audio clip’s two voice channels would be used on an audio track in the timeline, the sound effect channel on another track.
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### Editing workflow with streams
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A high-level picture of the 3 stages input, editing, and output:
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```
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INPUT ─────────────> TIMELINE ────────────> OUTPUT
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... | ... | @@ -43,4 +54,25 @@ CLIPS contain e.g. TRACKS to keep sound Video CONTAINER with |
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(other lang) → achieve sound image - Stereo
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TRACKS - 5.1 Surround
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→ distinguish topics
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``` |
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```
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The editing part is obviously the most complex. Three different concepts are of importance there:
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* **Remapping** of channels to decide which clip channels are used on the timeline track
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* **Panning** or, generally, changing the sound image, e.g. to convert from stereo to surround or the other way round; this influences the number of channels
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* **Submix tracks** which are like virtual track groups on which effects can be applied
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### Example project with audio streams
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An example of a more complex project could be the following:
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![image](uploads/2aede732c2073e145c9dcc3696ca868c/image.png)
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The goal in this project is to create a bilingual video file, each language track using 5.1 surround sound. It should be achieved from the sample audio input clips which may need some adjustment before they can be used. There is also a voiceover for the second language which is a stereo track recorded in post.
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What is happening in this imaginary project?
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1. When adding clips to the timeline, decide which channels should be used on the target audio track. A2 is a stereo track, and the voice channels from clip 2 need to be swapped (CH1 goes to the track’s CH2 and vice-versa). The effect is a mono track but should be heared as surround effect, which is accomplished by the panning.
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2. A1 and A3 are first combined in a submix track: the two 5.1 tracks are reduced to one 5.1 track. Now there is keyframed volume control on the combined result.
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3. Finally, all channels are routed to the master track which is another virtual submix track, with the difference that it has 18 input channels so the languages can be routed to separate output tracks. The voices are also mapped to 5.1 with a panning effect. |
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