video - VLC 2.2 and Levels -

i have application i've written provide simulated mp4 camera streams "black box". use irony quotes because don't have access sources, have support contract vendor makes it.

this black box supports h.264 level 2.2. not use sdp, expects camera streams 640x480 @ 30hz. understand reasonably standard output surveillance cameras.

so application using vlc (libvlc specific) stream mp4 files device. have working fine (with one minor exception, that's separate issue). however, vlc 2.1.5. when tried upgrading latest 2.2.1, instead of videos on other side of our black box seeing whiteish-gray squares.

our vendor looked on wireshark dumps, , told me vlc 2.2.1 stream reporting level 5.1 instead of 2.2, , using high profile instead of baseline or main. looks vlc trying "upgrade" (transcode?) video on me, , that's messing reader on black box.

is there way old behavior vlc 2.1.5 back, or force use level , profile of choosing?

h.264 profiles

profiles sets of capabilities. if black box supports baseline profile it'll not able decode stream using high capabilities.

in vlc can set h.264 profile used x264 encoder this:

--sout="#transcode{vcodec=h264,venc=x264{profile=baseline}...

h.264 levels

think of levels constraint/indicator of required decoder performance. if decoder supports level profile must able decode streams @ level , of lower levels.

first of all, level 640x480 @ 30 fps 3 , not 2.2.

you can calculate following:

macrobolocks = ceil(640/16) * ceil(480/16) = 1200 macroblocks/s = macroblocks * 30 = 36000 

the reason ceil non-mod16 resolution padded multiple of 16.

you take @ h.264 levels. within frame size limit 2.2 1620 max decoding speed greater 20252 have choose next level wich 3. you'll have consider maximum bitrate baseline profile in table.

if have android device can download h.264 calculator app amazon app store (i can send apk if don't orwellian app permissions)

the x264 encoder automatically choose level based on encoding parameters. vlc can set flag using like:

--sout="#transcode{vcodec=h264,venc=x264{profile=baseline,level=22}"...

beware, sets encoder output flag , doesn't produce level 2.2 stream. can put values want, it's possible mark full hd stream @ 60 fps level 2.2 if it's level limits.

vlc transcoding

if want make sure you're sending correct stream you'll need transcode source material. example 640x480 @ 30 fps results in level 3 h.264 stream showed above. if want level 2.2 you'll need lower resolution or framerate or both. video bitrate can go lower in case.

cvlc input.mp4 --sout="#transcode{vcodec=h264,venc=x264{profile=baseline},fps=30,width=640,height=480,vb=1372,acodec=mpga,ab=128,channels=2,samplerate=44100}:rtp{...}

mediainfo

mediainfo great tool information media file. can check specs of input files, won't detect wrong level forced or wrongfully chosen encoder. safest way re-encode.