
On 2023-06-20 10:50, Lennart Sorensen wrote:
https://www.fpga4fun.com/files/HDMI_Demystified_rev_1_02.pdf gives a nice explanation of how it worked in HDMI 1.3. 2.1 just got rid of the dedicated clock to free up a 4th signal pair.
Other than a small bit about lip sync, there is nothing about syncing the signal in that.
Sure but HDMI and compressed video of IP have nothing in common really. Vastly different bandwidths and purposes.
First off, that RTP article mentions video, not just audio. While the details may differ, the principles remain the same, that is the framing is embedded in the data. Don't confuse transport with signal. In the case of my IPTV, the exact same signal is delivered to my TV, as I would receive over the old digital system. And they both use HDMI to reach my TV. By comparison, consider the audio in cell phones. Way back in the dark ages of "1G" phones, the signal was analog. Then came 2G, with a few different methods (CODECs) of converting the audio to a digital signal, with a major goal being to reduce the bandwidth, to the point where three or so digital calls would use the same amount of spectrum as one analog. The difference between 2G and 3G, which used the GSM CODEC, is with 2G, the data was a continuous stream, but with 3G the exact same audio was transmitted in packets, though not over IP. Saving bandwidth was still a goal. Then, with 4g and lots of bandwidth available, the goals shifted from saving bandwidth to providing a better quality call. IP was now being used to carry the calls. Through all this, the goal remained the same, that is to carry a voice conversation. With the digital systems, the sync was carried along with the call data, even though different CODECs might have been used at different times. Again, there is absolutely no need for blanking intervals with digital TV. I suspect Hugh's question arises because he is using an analog monitor, if I read his post correctly. Then analog framing, including blanking interval, has to be created. BTW, it is possible to have analog video without blanking intervals. Back in the 70s, I used to maintain some video terminals where the sync was fed directly to the monitor, instead of being combined with the video.