Member Avatar for SAZAR

Made an experiment:
1. connected SONY camera's composite out to computer audio line-in
2. recorded incoming audio/video signal as sound using SoundForge program (stereo recording - one recorded audio (can clearly hear it), the other channel is video (hear as noise)); saved as WAV file
3. copied WAV file onto MP4 player
4. used composite audio/video cable (came with SONY camera), connected it to stereo audio output of MP4 player - connected it to TV

Results:
- heard audio signal (nothing special)
- picture on TV was just some noise (experiment failed)

-------

What went wrong here? How come picture didn't show?
How can it be made work?

---------------------------

Idea for this interesting little experiment came to me when I thought about if it is possible to make a program for Pocket PCs (Smartphone) which don't have TV out to emulate audio/video signal using Pocket PCs earphone terminal.

Can such program be made?

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  • Latest Post Latest Post by Member #1130142

Dani AI

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Nice hands‑on test, — good thinking. As pointed out, the earphone/line path will reproduce the audible portion but not the composite video waveform and its timing. The composite signal is a single analog waveform that combines luminance, chroma and short, precisely timed sync pulses; TVs expect that exact waveform and termination. For anyone trying to recreate or carry that waveform over an audio path, the mismatch in both spectrum and timing is the core problem. (en.wikipedia.org)

Why it fails in practice: standard-definition analog video contains frequency content and timing components that lie far above what consumer audio paths and phone headphone outputs are designed to pass. Generating or capturing that content requires hardware and sampling clocks in the MHz range and proper video termination; ordinary audio outputs are AC‑coupled and not 75 Ω video drivers, so DC levels and very short sync pulses get lost or distorted. That’s why replaying a WAV through the headphone jack can give sound but not a stable picture. (en.wikipedia.org)

What will work (practical options): use a proper composite capture device (USB analogue‑to‑video capture) to digitize the camera feed, or convert RGB to composite with a dedicated encoder IC if building hardware (the AD725 family is an example of an RGB→NTSC/PAL encoder). For phone output, use the phone’s supported video‑out path (HDMI/MHL or USB‑OTG plus an external encoder) rather than the earphone jack. If the goal is research/hobbyist decoding from scope traces, you need a fast digitizer (multi‑MHz) and a software CVBS decoder/time‑base corrector — projects such as the cvbs‑decode toolchain show that workflow. (elgato.com)

Concrete, short checklist:

  • To record: feed the camera’s composite into a USB capture dongle and record on PC.
  • To output from a phone: use hardware video‑out or an external encoder (do not use headphone jack).
  • For DIY TV‑out: use an encoder IC or a device with native TV‑out (Raspberry Pi, certain SoCs) and drive a 75 Ω cable at the correct level.
    Always respect video impedance/levels (composite is a 1 Vpp, 75 Ω signal) and avoid direct headphone→video hookups — improper connections can cause no image and risk damaging equipment. (en.wikipedia.org)
Member Avatar for SAZAR

...What? This issue is not interesting for you?

Member Avatar for SAZAR

...I don't believe it. No one answered yet...

Member Avatar for gegrove

Made an experiment:
1. connected SONY camera's composite out to computer audio line-in
2. recorded incoming audio/video signal as sound using SoundForge program (stereo recording - one recorded audio (can clearly hear it), the other channel is video (hear as noise)); saved as WAV file
3. copied WAV file onto MP4 player
4. used composite audio/video cable (came with SONY camera), connected it to stereo audio output of MP4 player - connected it to TV

Results:
- heard audio signal (nothing special)
- picture on TV was just some noise (experiment failed)

-------

What went wrong here? How come picture didn't show?
How can it be made work?

---------------------------

Idea for this interesting little experiment came to me when I thought about if it is possible to make a program for Pocket PCs (Smartphone) which don't have TV out to emulate audio/video signal using Pocket PCs earphone terminal.

Can such program be made?

I need something like this but from a Scope I can see the video wave Form so how do I convert this to AVI the output is has only X And Y values

Member Avatar for Member #1130142

I admire your curiosity and experimentation! However, the video signal has a much higher bandwidth than audio. Most domestic sound cards will record audio up to about 20 kHz - this is limited by the sample rate, which is normally 44.1 kHz. The sound card will filter off anything above 20 kHz to prevent aliasing. In contrast a standard definition composite video signal has a bandwidth of about 5.5 MHz. Crucially the synchronisation pulses that the TV needs to display the picture have a duration of just 4.7 micro seconds so with such a low sampling rate on the sound card, these are essentially removed. Similarly the output from a phone can only go up to about 20 kHz so cannot generate a video signal - sorry!

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