Quick Answer: An AV plug in US practice is three RCA connectors: yellow composite video, white and red audio. HDMI cannot be driven from those wires, so a converter has to digitise the video, deinterlace it, scale it to 720p or 1080p and embed the two audio channels. Expect 480i in, 1080p out, 16 to 50 ms of latency and no detail beyond the roughly 5 MHz the source carries. Set the 4:3 or 16:9 switch to match the material, not the display.
Three RCA plugs carry one video channel and two audio channels as analogue voltages, and an HDMI sink will not accept either. The purchase decision is therefore about the quality of four internal stages, not about plug compatibility, because every unit on the shelf has the same three sockets.
The four jobs inside the box
First, an analogue to digital converter samples composite video at 4 times the subcarrier, around 27 MHz, and produces 8-bit samples. Second, a decoder separates luma from chroma on that 3.58 MHz subcarrier, which is where most cheap units lose colour resolution. Third, a deinterlacer turns 60 fields into 60 frames. Fourth, a scaler resamples 720 by 480 to 1280 by 720 or 1920 by 1080 and repeats the audio as 48 kHz stereo.
Why the yellow plug is the limit
Composite video multiplexes brightness, colour and sync into one conductor, so the decoder has to guess which part of the waveform is which. That is why red text on a blue background crawls at the edges even on a good converter, and why S-video or component sources look cleaner through the same box. At 480i the source carries about 5 MHz of luma and 1.3 MHz of chroma, so the decoder has roughly 700 samples per line to work with, and text smaller than 12 pixels high in the original frame is illegible after scaling. The fault is in the source format, not in the HDMI output stage.
Geometry: 4:3, 16:9 and letterbox
A 4:3 source on a 16:9 panel needs pillarboxing, and a widescreen source flagged as 4:3 needs the converter’s 16:9 setting so the display does not stretch it twice.
Stretch, pillarbox or crop
A converter that ignores the flag will produce a picture where circles are ellipses, and no display setting can undo it cleanly. If the material is mixed, set 4:3 as the default and change it per source rather than per session. Overscan in the display hides another 5 per cent of each edge, so confirm that the converter output is not already inset before blaming the geometry.
Converter options compared
All units take three RCA inputs unless stated; output timing is switchable on the better models.
| Converter | Video in | Video out | Latency | Audio |
|---|
| Basic composite box | 480i60 | 720p60 | 16 to 30 ms | stereo, embedded |
| Composite with scaler | 480i60 | 1080p60 | 20 to 40 ms | stereo, embedded |
| Composite and S-video | 480i60 | 720p or 1080p | 20 to 40 ms | stereo, embedded |
| Component to HDMI | 480p to 1080i | 1080p60 | 10 to 25 ms | stereo, embedded |
| Four-input RCA switch | 480i60 | 1080p60 | 20 to 40 ms | stereo, embedded |
Practical scenarios
- Situation: Old games console on a modern television. Convert to 720p to keep latency near 16 ms, and connect through a display with a game mode rather than adding a second scaler in the television.
- Situation: VHS archive transfer to a capture card. Convert to 1080p only if the capture device refuses 480p; otherwise keep 480p so the file stays close to the source.
- Situation: Two displays from one converter. A passive hdmi y splitter will not work, because HDMI is a point to point link with no arbitration; use a powered splitter rated for the output timing.
- Situation: Long cable from converter to projector. Keep the HDMI leg under 15 ft (4.5 m) at 1080p60 and choose a lead by its category rather than its version number, as explained for hdmi 2.2 cable listings.
When the converter is the wrong tool
If the source is already digital, conversion is unnecessary work: a set-top box with HDMI should go straight to the display. If the source has component output at 1080i, a component to HDMI converter gives a much better result than composite through the same chassis. And if the run between rooms is the problem, the right part is a cable rated for the distance, not a converter with a longer lead; the Ethernet channel carried in hdmi to hdmi with ethernet leads does not extend video and is not a substitute for a proper extender.
FAQ
Do I need a converter for each source device?
Yes, unless you buy an input switch with three or four RCA inputs and one HDMI output. A converter with a single input means swapping cables, which wears the sockets and is the most common cause of a loose centre pin.
Why is the picture black and white?
The chroma subcarrier is missing or the colour standard is mismatched, so the decoder sees luma only. Check that the yellow plug is in the video socket and not the green component socket, then check the converter’s NTSC and PAL setting.
Can the converter output 4K?
Some units upscale to 3840 by 2160, but the source holds about 5 MHz of detail, so the extra pixels are interpolation. Buy for reliable 1080p output and let the display handle the final scale, which is usually better than the converter’s.
