Document the YUV420 to O_UYY_E_VYY transformation (AEGHB-1280)

[sjaramillo-yx]

Checklist

• Checked the issue tracker for similar issues to ensure this is not a duplicate.
• Described the feature in detail and justified the reason for the request.
• Provided specific use cases and examples.

Feature description

Include documentation about how and where the transformation from YUV420 planar to O_UYY_E_VYY packets takes place. Right now there's no clarity about how this library adjusts the buffers taken from a camera device to prepare them for the H264 P4 hardware encoder.

Use cases

This would be important for projects that use the esp_cam_sensor and esp_h264 libraries outside of esp_video (for whatever reasons)

Alternatives

The esp_image_effects is an alternative, but it only compiles under ESP IDF v5.3 for the P4 chip and esp_cam_sensor does not compile unit IDF v5.4

Additional context

I'm trying to use esp_cam_sensor and esp_h264 outside of esp_video to have more control over the buffers and allocations, as well as removing some abstraction from my application, but I need to modify the I420 buffers to feed them to the encoder and right now I'm doing so manually, but I'm sure there's a better way implemented in esp_video, I just can't seem to find it

[WangYuxin-esp]

Can I know what camera sensor you're using?

[sjaramillo-yx]

I'm using an OV5647, but I'll mark this as closed since after I wrote this issue Espressif released the latest version of the Technical Reference Manual for the P4 and specified that the ISP outputs not YUV420, but O_UYY_E_VYY when configured in YUV420 mode, so no conversion is necessary.