Concretely, a horizontal or vertical flip is applied as a filter, which needs a re-encode because the coded frames themselves change; the audio stream is copied through untouched. You choose the axis — horizontal produces a mirror image, vertical produces an upside-down reflection — and the whole file is transformed on it.
What is the difference between flipping and rotating?
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A flip reverses the content across an axis and produces a mirror image; a rotation turns it without reversing anything. Text is the giveaway: it reads backwards after a flip and stays readable after a rotation.
Does the source format matter when flipping?
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It does. MPG is the same MPEG-1/2 program stream under the shorter extension, still the format of DVD-era captures. That is what decides whether the mirror can be done by rewriting the file or requires decoding it first.
Anything specific to MPG to be aware of?
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Yes — a .mpg is the same program stream as .mpeg, and both come out of DVD-era capture hardware with interlacing still baked in. Worth a moment before you flip something you cannot easily recreate.
When would I actually want to flip rather than rotate?
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Correcting a scan or a webcam capture that came out mirrored, making a symmetrical pair from a single asset, or matching the direction a subject faces to a layout. If the content contains text, logos or numbers, check the result — those mirror too.
Can I flip several files at once?
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Yes. The same axis is applied to every file in the batch, which is how you fix a whole folder of mirrored captures in one pass instead of one at a time.
