what is COLOR_FormatYUV420Flexible?

Question

I wish to encode video/avc on my android encoder. The encoder (Samsung S5) publishes COLOR_FormatYUV420Flexible as one of its supported formats. yay!

but I dont quite understand what it is and how I can use it. the docs say:

Flexible 12 bits per pixel, subsampled YUV color format with 8-bit chroma and luma components.

Chroma planes are subsampled by 2 both horizontally and vertically. Use this format with Image. This format corresponds to YUV_420_888, and can represent the COLOR_FormatYUV411Planar, COLOR_FormatYUV411PackedPlanar, COLOR_FormatYUV420Planar, COLOR_FormatYUV420PackedPlanar, COLOR_FormatYUV420SemiPlanar and COLOR_FormatYUV420PackedSemiPlanar formats

This seems to suggest that I can use this const with just about any kind of YUV data: planer, semi-planer, packed etc. this seems unlikely: how would the encoder know how to interpret the data unless I specify exactly where the U/V values are?

is there any meta-data that I need to provide in addition to this const? does it just work?

Answer 1

Almost, but not quite.

This constant can be used with almost any form of YUV (both planar, semiplanar, packed and all that). But, the catch is, it's not you who can choose the layout and the encoder has to support it - it's the other way around. The encoder will choose the surface layout and will describe it via the flexible description, and you need to support it, whichever one it happens to be.

In practice, when using this, you don't call getInputBuffers() or getInputBuffer(int index), you call getInputImage(int index), which returns an Image, which contains pointers to the start of the three planes, and their row and pixel strides.

Note - when calling queueInputBuffer afterwards, you have to supply a size parameter, which can be tricky to figure out - see https://stackoverflow.com/a/35403738/3115956 for more details on that.