GitLab

This class supports pixel conversions and rescaling, backed up by both
libyuv functions for SW conversions and PixelBufferTransferer for HW
conversions. It supports conversions from all supported capture formats
(NV12, YUY2, UYVY, MJPEG) to NV12 and I420. (The pixel transfer path
supports even more destination pixel formats, but libyuv's destination
must be NV12 or I420, and these are the only two of interest to us.)

Whether HW or SW conversion is used, the resulting buffer is put in an
IOSurface-backed pixel buffer.

Code paths:
- When we have a pixel buffer, i.e. this is NOT MJPEG:
  - PixelBufferTransferer: X -> I420/NV12 in a single step.
  - libyuv: X -> I420 in a single step. X -> NV12 may involve an
    intermediate step X -> I420 -> NV12. Conversion and rescaling are
    done in separate steps.
- MJPEG (when we only have a sample buffer):
  - PixelBufferTransferer: Not supported.
  - libyuv: MJPEG -> I420 in a single step. MJPEG -> NV12 in two steps
    MJPEG -> I420 -> NV12. Conversion and rescaling are done in separate
    steps.

In a follow-up, we will do MJPEG -> NV12 in a single step based on the
libyuv CL that eshr@ recently landed.

Measurements show that which conversion method is most efficient is
dependent on input and output pixel formats and may even be affected by
cache hits/misses. In future CLs, we should wire up and measure the
optimal SampleBufferTransformer configurations (in which formats to use
libyuv and in which formats to use pixel transfer).

Bug: chromium:1132299
Change-Id: I4f6053c65c0c3b02483d130e25bebd1f656abd89
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2498563
Commit-Queue: Henrik Boström <hbos@chromium.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823502}