MP4 from a phone or DSLR

Goal: a good first picture of the Sun from a video recorded on a phone held to an eyepiece, or from a DSLR or mirrorless camera.

No output is shown here because the machine used for this manual has no ffmpeg. The commands, options and messages are as documented elsewhere in this manual; the messages are listed in Troubleshooting.

What to expect

An MP4 is compressed, and the compression throws away fine detail first, which is exactly what stacking needs. Helia can stack it and the picture will be a big step up from a single frame, but a raw SER or AVI from an astronomy camera keeps more. See When an MP4 is fine. When you open one, the Open step says so: lossy 8-bit 4:2:0 video (h264): fine for quick results, SER/AVI raw captures keep more detail.

1. Install ffmpeg

Helia never bundles ffmpeg; it runs it when it is installed (version 4.4 or newer).

Check with ffmpeg -version. See Installation.

2. Record well

• Solar filter first. Never point a phone or camera at the Sun without a proper solar filter over the front of the telescope.
• Lock exposure and focus, so the brightness does not wander. Record a minute or more, at the highest frame rate the phone offers, with the Sun fully in frame.
• Keep the phone steady (a clamp), and use a self-timer or remote so you do not shake it.
• Put the filter in the file name when you copy it off the phone: sun_Ha_001.mp4 or sun_white_001.mp4. A phone names videos VID_2026...mp4, which tells Helia nothing.

3. Open and stack

In the app, open the file as for any other. A notice shows Converting the video with ffmpeg with a percentage while the frames are decoded once to a cache folder; afterwards scrubbing is as quick as for a SER file. The decoded frames are uncompressed, so the cache needs room for the whole video; Helia checks first.

On the command line:

helia info sun_white_001.mp4
helia stack sun_white_001.mp4 -o sun.tif --preset white --sharpen wavelet

helia info is the quick test that ffmpeg is working. To use a drive with more room for the decoded frames, add --cache-dir /big/disk.

4. Choose what to keep

• Keep the recommended share of frames to begin with, and compare with a smaller and a larger one on the quality curve (Analyse). With a lossy video the sharpness measure partly ranks how the encoder behaved, so the best frames are less clear cut than in a raw capture.
• Go easy on the sharpening. Wavelets at the recommended values are fine; deconvolution will turn compression blocks into texture.

Colour video

A phone video is already a colour picture. Helia stacks colour video as luminance, or as the red, green or blue channel you choose (--channel, or the Channel chips under Advanced settings). For a white-light video leave it at luminance (lum) or choose green (g). The stack is mono, and the colour of the finished picture comes from the look you choose; see Can it stack colour?.