问题
In my use-case I have to provide codec specification within the HTML5 video source's MIME type. But even a type="video/mp4; codecs=avc1" is not detailed enough for Firefox. Firefox needs the extra detail of for example type="video/mp4; codecs=avc1.64001E". My problem is that I don't know where to get this 64001E part from.
The whole identification happens on server side. So far I was using ffprobe and that's perfectly supplies me JSON format output, like so:
ffprobe -select_streams v:0 -v info -of json -show_entries stream=codec_name,level,profile,width,height -i 1CE89B23-F9BD-43B9-805B-C49ACA9E5FFB_xxxxxxx.mp4
"streams": [
{
"codec_name": "h264",
"profile": "High",
"width": 1080,
"height": 1920,
"level": 50
}
]
}
I can get the profile and the level, but nothing like 64001E. In my local environment I also have mediainfo:
mediainfo 8038B652-106B-4FBB-BAD6-AF7E32913FDE_xxxxxxx.mp4
General
Complete name : 8038B652-106B-4FBB-BAD6-AF7E32913FDE_xxxxxxx.mp4
Format : MPEG-4
Format profile : Base Media
Codec ID : isom (isom/iso2/avc1/mp41)
File size : 1.18 MiB
Duration : 6 s 634 ms
Overall bit rate : 1 496 kb/s
Writing application : Lavf57.83.100
Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L3
Format settings : CABAC / 5 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 5 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 6 s 634 ms
Bit rate : 1 396 kb/s
Width : 360 pixels
Height : 480 pixels
Display aspect ratio : 0.750
Frame rate mode : Constant
Frame rate : 30.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.269
Stream size : 1.10 MiB (93%)
Writing library : x264 core 152 r2854 e9a5903
Encoding settings : cabac=1 / ref=5 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=8 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=2 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=15 / lookahead_threads=2 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=3 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=50 / rc=crf / mbtree=1 / crf=17.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
Codec configuration box : avcC
Audio
ID : 2
Format : AAC LC
Format/Info : Advanced Audio Codec Low Complexity
Codec ID : mp4a-40-2
Duration : 6 s 632 ms
Duration_LastFrame : -9 ms
Bit rate mode : Constant
Bit rate : 90.4 kb/s
Channel(s) : 1 channel
Channel layout : C
Sampling rate : 44.1 kHz
Frame rate : 43.066 FPS (1024 SPF)
Compression mode : Lossy
Stream size : 73.2 KiB (6%)
Default : Yes
Alternate group : 1
What we see here is that the AAC part has a longer Codec ID mp4a-40-2, but the video stream is still just avc1.
I'm looking at lists https://tools.woolyss.com/html5-canplaytype-tester/ and https://wiki.whatwg.org/wiki/Video_type_parameters and I think maybe there's a programmatic way to convert the codec profile + level to the code what the MIME type codec specification has.
In https://developer.mozilla.org/en-US/docs/Web/Media/Formats/codecs_parameter I see that "avc1.4d002a" means Main Profile, Level 4.2. Looking at the list I linked earlier I figured that the 6 hex digits can be broken down into groups of two. The last two is the level. In this latest example the Level is 4.2, we just have to remove the dot => it becomes 42, which is 2a hex. The other 4 hex digits are related to the profile as Main, High, etc and then Progressive, but I haven't found a definition yet, and I wonder if the ffprobe is able to output things like High 4:2:2 Intra Level or High Progressive Level. We'll see.
https://tools.ietf.org/html/rfc6381#page-12 has some examples, but I followed the links and still don't see any definitive list or anything.
The ITU-T H.264 specification Annex A lists 14 profiles. In those listings there's a profile_idc mentioned, which seems to be the decimal for the first two hex digits, for example High's profile_idc is 100 decimal, which is 64 hexa. Now we just need to figure out the middle two hexa digits. Preferably a GitHub repo source file would be great where these things are curated into a sane concise const literal array.
回答1:
It is described in e.g. Mozilla link ("PPCCLL is six hexadecimal digits specifying the profile number (PP), constraint set flags (CC), and level (LL)"). If you don't find a tool fitting your needs, we could extend e.g. MediaInfo for that, let us know.
Note: the CC indicated in the list are the expected flags, not the ones really in the file, it should be OK 99.99% of the time but you can not be sure it is the real content. MediaInfo internally reads the flags but it does not export them for the moment.
来源：https://stackoverflow.com/questions/59891176/how-can-i-or-is-it-possible-to-convert-the-avc-codec-profile-and-level-to-the