c_mpos: jpegdec, a native JPEG decoder module (esp_new_jpeg) for video playback - #305

What

A jpegdec MicroPython module in c_mpos, wrapping Espressif's esp_new_jpeg decoder (pulled in through the IDF component manager in build_mpos.sh, the same way adc_mic is):

import jpegdec
w, h = jpegdec.info(jpeg_bytes)
out = bytearray(w * h * 2)               # RGB565 little-endian, 16-byte aligned
jpegdec.decode(jpeg_bytes, out)          # optional: scale_w, scale_h (multiples of 8, up to 1/8)

The output buffer goes straight into an lv.image_dsc_t with cf=RGB565, so LVGL blits it like a raw frame: no LVGL decoder, no image cache.

Why

MJPEG video in ClipTV. LVGL's own TJpgDec path needs LV_USE_FS_MEMFS to read from RAM at all (lvgl_micropython#14), costs about 100 ms per 160x120 frame and 250 ms per 320x240 frame, and keeps every decoded frame in a pointer-keyed cache that fills the heap.

Measured (Waveshare ESP32-S3-Touch-LCD-3.5)

In-app MJPEG playback with this module: 160x120 at 15 fps plays at 13.9 fps and 320x240 at 8 fps plays at 7.8 fps, both paced to the clip with no frame skipping; the decoder is no longer the bottleneck (storage reads are).

Cost and scope

• The prebuilt decoder library takes about 74 KB of firmware: esp32s3 partition headroom drops from ~93 KB to ~19 KB. Worth knowing before merging.
• ESP32 family only (esp32, s2, s3, p4); the idf_component.yml rule limits the dependency to those targets, so other builds are unaffected.
• Errors map to ValueError (bad/truncated/unsupported JPEG), MemoryError and RuntimeError.

Image size (update 2026-09-27)

The decoder adds ~75 KB to every ESP32-family image, which pushed both OTA app partitions past their size in CI (esp32 by 38.7 KB, esp32s3 by 51.1 KB). Growing the partitions would break OTA updates for devices in the field, so the two extra commits trim ESP-IDF features that no MicroPythonOS board or app uses instead:

1. build: drop ESP-IDF features no MicroPythonOS board or app uses — PPP (network.PPP; no board has a modem), DTLS (the ssl module never speaks TLS over UDP), the TLS server side (nothing serves HTTPS; ssl stays fully functional as a client, client certificates included) and the BLE 5 controller features (the bluetooth module only does legacy advertising/scanning).
2. build: drop IPv6 from the ESP32-family images — kept separate because it is the one trim a user could notice (sockets are IPv4-only afterwards). Everything the OS and its apps talk to is reachable over IPv4. If you would rather keep IPv6, drop this commit: the first one alone already makes CI green, just with only 10 to 13 KB of headroom left.

CI measurements on this PR (app partitions: esp32 3,737,600 B, esp32s3 3,670,016 B):

For scale, the image is dominated by the frozen Python (~917 KB), secp256k1 (~150 KB, already at the smallest precomputation), the LVGL binding and lodepng; the built-in app filesystem is already compressed and every enabled font is referenced, so there was nothing cheaper to cut.

Verified on a Waveshare ESP32-S3-Touch-LCD-3.5 running the image with both commits: boots normally, HTTPS fetches from badgehub.eu and updates.micropythonos.com succeed, a BLE scan sees 15 devices and legacy advertising works, network.PPP is gone.

🤖 Generated with Claude Code

With thanks to the scientists and engineers who did the hard, unglamorous work that got us here.