3

I want to do video captures with a video4linux2 device.

The video data contains a lot of darker shades of grey.
When I capture a single PNG file, everything is fine.
Capturing with ffmpeg/avconf using x264 truncates my color space to 16..235.

I tried to define -color_range 2 but it didn't have any effect.
I also played with the different pixel formats (yuv444p, yuv420, ..) --without success.

This is the command line which produces the reduce color range video:

$avconv -f video4linux2 -i /dev/video0 -vcodec libx264 -pix_fmt yuv444p -color_range 2 -crf 14 -t 120 -y out.mp4

avconv version 0.8.17-4:0.8.17-0ubuntu0.12.04.1, Copyright (c) 2000-2014 the Libav developers
  built on Mar 16 2015 13:26:50 with gcc 4.6.3
[video4linux2 @ 0x2044b60] Estimating duration from bitrate, this may be inaccurate
Input #0, video4linux2, from '/dev/video0':
  Duration: N/A, start: 1445936359.182177, bitrate: 890634 kb/s
    Stream #0.0: Video: rawvideo, yuyv422, 1280x720, 890634 kb/s, 60.40 tbr, 1000k tbn, 60.40 tbc
[buffer @ 0x20450a0] w:1280 h:720 pixfmt:yuyv422
[format @ 0x2046d20] auto-inserting filter 'auto-inserted scaler 0' between the filter 'src' and the filter 'Parsed filter 0 format'
[scale @ 0x2047660] w:1280 h:720 fmt:yuyv422 -> w:1280 h:720 fmt:yuv444p flags:0x4
[libx264 @ 0x2045fe0] using cpu capabilities: MMX2 SSE2Fast SSSE3 FastShuffle SSE4.2 AVX
[libx264 @ 0x2045fe0] profile High 4:4:4 Predictive, level 4.0, 4:4:4 8-bit
[libx264 @ 0x2045fe0] 264 - core 120 r2151 a3f4407 - H.264/MPEG-4 AVC codec - Copyleft 2003-2011 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x1:0x111 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=1 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=4 threads=12 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=0 b_adapt=1 b_bias=0 direct=1 weightb=0 open_gop=1 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=14.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.25 aq=1:1.00
Output #0, mp4, to 'out.mp4':
  Metadata:
    encoder         : Lavf53.21.1
    Stream #0.0: Video: libx264, yuv444p, 1280x720, q=-1--1, 302 tbn, 60.40 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo -> libx264)

My last tries were to define a color matrix to manually scale 0..255 to 16..235, so that I will end up with a slightly compressed, but a least complete color space.

But this resulted in an error from avconf

$ avconv -f video4linux2 -i /dev/video0 -vcodec libx264 -pix_fmt yuv444p -color_range 2 -vf 'format=yuv444p,colormatrix=bt709:bt601' -crf 14 -t 120 -y out.mp4

avconv version 0.8.17-4:0.8.17-0ubuntu0.12.04.1, Copyright (c) 2000-2014 the Libav developers
  built on Mar 16 2015 13:26:50 with gcc 4.6.3
[video4linux2 @ 0xabbb60] Estimating duration from bitrate, this may be inaccurate
Input #0, video4linux2, from '/dev/video0':
  Duration: N/A, start: 1445936333.196864, bitrate: 890634 kb/s
    Stream #0.0: Video: rawvideo, yuyv422, 1280x720, 890634 kb/s, 60.40 tbr, 1000k tbn, 60.40 tbc
[buffer @ 0xac0ee0] w:1280 h:720 pixfmt:yuyv422
No such filter: 'colormatrix'
Error opening filters!

Do you know how to get ffmpeg to encode the full color range?

2

In this case, the problem didn't come from ffmpeg/avconv.

The rawvideo source I use offers different color formats to be used:

  • argb32
  • rgb24
  • bgr24
  • yuv444
  • yuv420
  • [...]

When I extract a png file (which was fine), the bgr24 color format is used. When I capture a video, avconv automatically chose one of the yuv formats. I guess the clamping to (16..235) did happen in the driver itself, that's why I couldn't influence it.

By giving the parameter -input_format bgr24 to the input device, I chose the unclamped value range and the capturing worked fine.

Final command line, with yuv420p as target format which produces even a Windows Media Player complatible output:

avconv -f video4linux2 -input_format bgr24 -i /dev/video0 -vcodec libx264 -pix_fmt yuv420p -color_range 2 -crf 14 -t 120 -y out.mp4

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