Silly question about HDMI:why uncompressed video but mostly compressed audio?

That's a question I've been wondering plenty of times. When an audio/video signal is sent through a HDMI cable/interface, for example when one is playing the average BD disc with a DTS-HD Master Audio or Dolby TrueHD audio track, or the same with almost 4K video from an UHD BD disc, most of us (not to say all) have are players audio set up to "bitstream" so the lossles (or lossy) codecs are sent untouched via HDMI so the AVR does both decoding/decompressing and volume level control and amp.
But when it comes to video it's the player the one that decodes and decompresses the video stream and do other processing and sends a high bandwith uncompressed video signal through the HDMI cable which is to be received by the T.V.'s HDMI input which I guess does further processing to video.
Wouldn't it have been better to follow the same route as with audio codecs and send video undecoded and untouched through the HDMI interfaces/cable and let the video disc player just read, do error correction and pass both undecoded and untouched video and audio streams to both a T.V. set for its decoding/decompressing and processing and an AVR for its decoding/decompressing and processing. Doing it that way we could have used USB 3.0 without the need of a new standard. If I can record a 66 Gig double layer BDLX-R with an external BD recorder from a original UHD BD using an USB 3.0 port in around 2 hours for a movie that lasts 2 hours + (Star Wars, The Last Jedi), then USB 3.0 could be used to send compressed Hi Res Audio and 4K HDR video for later processing at their proper devices.
Or was HDMI just something new to sell to us? Is there any advantage to send uncompressed HD or UHD video with HDR via HDMI?
Am I just being plain dumb?

 

At a high level: the video is not "decompressed" by the player in the same manner that audio can be. It's in a container, that houses a file compressed with a codec. The player is converting the codec to RGB or YCbCr, which is what TVs were designed to accept.

You can use USB protocol to send MP4/MKV containers to modern TVs and let them convert the video to YCbCr/RGB. This takes more processing and flexibility in the TV. In short, it's cheaper/easier for TVs to be designed to accept YCbCr/RGB vs. a wider variety of containers.

 

But to have HD and 4K/UHD Video with HDR HDMI
is not really necessary. I forgot how many UHD MKV videos I've playera from a USB thumb drive connected to my Samsung's USB input and they played flawlessly in 4K and HDR.
I really don't understand the need of such a high speed connected to send raw uncompressed video suena It could be sent compressed as It comes from the disc player. A connection capable of around 150 Meg/sec would suffice as 4K HEVC compressed video maxes out at 100 Meg/sec and DTS-HD MA or Dolby TrueHD both with metadata for object based audio maxes out at around 10 Meg/sec or less, leaving still banwidth for figure codecs. Disc players would be simpler and cheapest also, for the sale price of an average player's price better disc transports could be used.
Anyway, current 4K sets are required to have the video codecs so they can receive OTA, satellite and streaming 4K video with HDR or Dolby Vision.

 

I routinely master uncompressed material and view it on a calibrated UHD through HDMI (which is the only input we have on the display). The HDMI connector is not the bottleneck here, not with HDMI 2.0.

If you bypass Blu-ray and instead use digital files, you won't have any limitations on compression. You will need a spitload of drives -- we're adding another 64TB this weekend, which will bring us up to about 150TB of online storage in the office.

 

I believe you still have a misunderstanding about "compressed", and I realize this may be a language issue. When it comes to the major video codecs, i.e. MPEG-4, AVC, MPEG-2, they don't have to be "uncompressed" by the player, just "converted". As such, there is no bandwidth saved by doing the conversion in the TV vs. the player. And that conversion from (for example) MPEG-4 to YCbCr is handled inside the players decoder chipset, along with all the other player functions. So removing this function doesn't save any money, nor does it cut down on the bandwidth required to transmit the video via HDMI.

 

I think sending both video and audio signals uncompressed via another kind of port like USB 3.0 could handle that. Right now I'm testing the US releaseon UHD BD of Game Of Thrones and looking at the onscreen info provided by the Sony UBP X-800 says that the average video bit rate is around 70 to 80 megabits per second and the Dolby Atmos TrueHD 7.1 encoded audio track is around 5 and 6.5 megabits per second. Let's take things to extreme,video is around 95 megabits per second and audio is around 8 megabits per second, this gives a total of 103 megabits per second, let's round it up to 110 megabits per second. That is not by far what's being transmited by the HDMI port and cable. I know that the video signal 'though compressed is on component 4:2:0 format which is not a standard supported via the HDMI specs so here comes chroma upsampling to convert it to 4:2:2 or 4:4:4 digital component video or RGB video. If transmited uncompressed/undecoded by the disc player, chroma upsampling can be performed by the T.V. set. USB 3.0 is more than capable of doing what the latest version of HDMI does if video and audio is transmited uncompressed. I've watched several UHD BDRemux,that is, the movie on the UHD BD disc put untouched into a mkv container and my 49" Samsung 4K HDR set is more than capable of playing them without a single glitch, so, why the need of HDMI? Why the need of a high bandwith audio/video interface that can transmit uncompressed video when something like USB 3.0 can do the same sending compressed audio and video to be decompressed and processed by T.V. sets and AVRs? It makes sense on the professional world but it doesn't for home use. I suposse it's the need to sell us something new.

 

Video related Audio has for many years been the poor stepchild of video. HDMI is also there because of HDCP (high definition content protection) DRM (digital rights management) which the Hollywood Studios desire. as they want locked down. No HDCP or HDCP handshake issues, no watching it. 2/3 of HDMI is related to Copy Protection reasons.

 

This is a good point... HDMI specifically handles these video related functions with an information exchange between the source/destination. That exchange includes device capabilities (signal info., supported formats, etc.). I think as far as bandwidth goes, USB 3 tops out at 5 or 6 Gbps, and HDMI is 16 or 18 Gbps. Apparently the latest HDMI standard supports 48 Gbps.

 

You're right, HDMI makes sense from an encryption/copy protection point of view. I still remember when DSD could only be output from a SACD player either by analog connections on on the digital domain via Firewire and I think there was another propietary and copy protected connections. That was until HDMI 1.4 if memory serves me well that enabled HDMI to transmit encrypted DSD data streams, then Firewire disappeared, I remember Denon and I think Sony used Firewire too and all of a sudden some time in 2006 I think it disappeared.