Hi !
2015-05-07 15:53 GMT+02:00 Jean-Michel Hautbois
jean-michel.hautb...@veo-labs.com:
Hi,
I am playing a bit with the coda encoder on i.MX6 and try to get the
most quality out of it. So, I am trying to use the controls of the
driver, in particular h264_i_frame_qp_value and h264_p_frame_qp_value.
I can get something with the following pipeline :
gst-launch-1.0 -evvv v4l2src num-buffers=2000
device=/dev/v4l/by-path/ipu1-capture io-mode=dmabuf !
video/x-raw,width=1280,height=720,framerate=25/1,format=YUY2 !
v4l2convert device=/dev/v4l/by-path/ipu1-scaler capture-io-mode=dmabuf
output-io-mode=dmabuf-import !
'video/x-raw,width=640,height=360,format=NV12' ! v4l2video0h264enc
output-io-mode=dmabuf-import
extra-controls=controls,h264_i_frame_qp_value=24,h264_p_frame_qp_value=30,video_gop_size=32
! queue ! progressreport name=p2 ! h264parse ! matroskamux ! filesink
location=/data/test_encode_360p.mkv
With those values, I get ~800kbps for a 360p converted frame. This is nice :).
The same video as an input with only the bitrate parameter set is
not visually similar.
But, when trying to encode a 720p video with the same QP parameters,
it is not working (the first keyframe is not ok, seems to be a P frame
instead of I, as it is 2000 bits and should be ~4). I am keeping
the videoscaler in this second case, as it should be used as a color
converter.
Philipp, did you do some tests like this one ? Did you observe that
the encoder can maybe be too long to get a frame encoded when desired
quality is high ?
I have done more tests, and it seems to be related to the bitrate we
asked, and the input resolution...
Right now, I have a 360p@5Mbps, which works perfectly, and the same
source, in 720p with a bitrate up to 3Mbps is ok. But when I go
higher, I miss the I frames on some GOPs (very frequently the second
one).
I don't know if there is some limitations to what the CODA can do, but
1080p30 seems impossible @4Mbps at least... ?
Thanks for your advices !
JM
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