-----Original Message-----
From: Libav-user [mailto:[email protected]] On Behalf Of Carl Eugen
Hoyos
Sent: Montag, 29. August 2016 12:17
To: This list is about using libavcodec, libavformat, libavutil, libavdevice
and libavfilter.
Subject: Re: [Libav-user] Writing 16bit greyscale videos
2016-08-29 10:59 GMT+02:00 Masneri, Stefano <[email protected]>:
I have a small class that creates an h264 video from a set of input images.
I have some problems trying to write 16 bit input images: Conversion
to yuv420p format loses 8 bit of precision, and apparently x264 does
not support encoding 16 bit greyscale data.
H.264 does not support more than 14bit, x264 does not support more than 10bit
input.
Do you know of a codec that supports encoding a video using
AV_PIX_FMT_GRAY16BE pixel format (or anything similar)?
jpegls, png, tiff, dpx, sgi, ffvhuff, ffv1 (all lossless) Jpeg2000, but FFmpeg
needs the external library libopenjpeg for encoding
gray16 (lossy or lossless)
Carl Eugen
Thanks Carl. I am able to create the video with 16 bit greyscale images, but
when I try watching the video in VLC I only see a green image. Reading the
frames one by one (with a simple class which uses FFmpeg) I see a strange
behaviour: every second column of the video is zero, while the other are
exactly as the input fed to the class that created the video. I guess there is
somewhere a problem switching from uint16 to uint8, but I cannot figure it out.
Any hints?
Here's the output of ffprobe
D:\Code\VisualStudio\FFmpegApps\Win\VideoWriterApp>ffprobe -i test16bit.avi
ffprobe version 2.8.6 Copyright (c) 2007-2016 the FFmpeg developers
built with gcc 5.3.0 (GCC)
configuration: --disable-static --enable-shared --enable-gpl
--enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib
--enable-fontconfig --ena
ble-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray
--enable-libbs2b --enable-libcaca --enable-libdcadec --enable-libfreetype
--enable-
libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame
--enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg
--enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr
--enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab
--enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis
--enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264
--enable-libx265 --enable-libxavs --enable-libxvid --enable-lzma
--enable-decklink --enable-zlib
libavutil 54. 31.100 / 54. 31.100
libavcodec 56. 60.100 / 56. 60.100
libavformat 56. 40.101 / 56. 40.101
libavdevice 56. 4.100 / 56. 4.100
libavfilter 5. 40.101 / 5. 40.101
libswscale 3. 1.101 / 3. 1.101
libswresample 1. 2.101 / 1. 2.101
libpostproc 53. 3.100 / 53. 3.100
Input #0, avi, from 'test16bit.avi':
Metadata:
encoder : Lavf56.40.101
Duration: 00:00:40.00, start: 0.000000, bitrate: 854 kb/s
Stream #0:0: Video: ffv1 (FFV1 / 0x31564646), gray16le, 720x576, 849 kb/s,
25 fps, 25 tbr, 25 tbn, 25 tbc
Stefano, did you check if your dataset really spans all 16 bits? if not,
you might be lucky. otherwise 16-to-8-bit quantisation might do the
trick, but is outside the scope of ffmpeg AFAIK. one thing I also
haven't tried is copying gray16 into yuv444 and let h264 swallow it. the
idea is to split the 16-bit in 2 compartments. and fill Y and U only
(the empty V channel gives 8bit overhead).
x265 might one day support 16-bits maturely, but is not really
competitive yet in terms of ingest bandwidth with x264 ... at least from
my studies (compression ration is already well ahead of x264). HEVC
yields native grey16 support as far as the standard goes.
Best,
Peter
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