Transcoding to 1280x720 limited to 29.97 Hz

[KamistixX]

Hello everyone :)

First of all thanks to the devs for making great work on this image. I am having a pleasure using it on my new Vu+ Uno4K.

I am playing around with transcoder-setup plugin which is built-in the OpenVIX image, and it is working very well when set at 576p output. I can choose 25, 30, 50 or 60 Hz (fps) output and the picture is very smooth, the Uno4K SoC is powerful and doing a great job with its hardware transcoding.

However, I would like to choose 720p output image quality with 50 Hz (frames per second). With this setting (in openwebif or in plugin setup directly on the STB), I can only get a fixed 29.97 fps output, and the picture is stuttery. (which is normal, since the channels original quality is usually 1080i50 for HD and 576i50 for SD channels).
Even with setting manually a 25 Hz output, I get 29.97 Hz transcoded streams, no matter the setting I choose. This problem does not appear with 576p. (checked with VLC on a computer)

Is it a limitation to Uno4K ? Does it work normally on other models, or is it maybe a bug affecting all enigma2 boxes ? I have not tried other images.


Thanks for your help !

[twol]

Whatever the transcoding plugin thinks, I think the Arm chip (which the Uno4K and most of the 4K receivers use) is limited to specific frame rates

[KamistixX]

Whatever the transcoding plugin thinks, I think the Arm chip (which the Uno4K and most of the 4K receivers use) is limited to specific frame rates

Hi twol thanks for your answer :)

That would be a pity :( There is no reason a chip can encode at 29.97 fps but not at 25 fps ! This could be a bug...

I still have hope for a fix in a future update :) If I am not mistaken, Transcoding is powered by Gstreamer, which can get an update maybe ?

Also guys, do not hesitate to share your Transcoding experiences with your own STBs (Vu+ and others). Can it do 720p at 25/30 Hz ? Even 50/60Hz ? Thanks ! :)

[Trial]

Hi,
a chip has build in hardware and if this has not the ability to do certain things it cannot be "fixed" by an update. Transcoding is NOT done by gstreamer because software is far to slow to do such an amount of calculations.

ciao

[KamistixX]

Hi,
a chip has build in hardware and if this has not the ability to do certain things it cannot be "fixed" by an update. Transcoding is NOT done by gstreamer because software is far to slow to do such an amount of calculations.

ciao

Hello Trial,

You are right, the Uno4K CPU is way too weak to do software encoding. However Gstreamer is not only able to do software encoding, it can also take advantage of hardware acceleration for this encoding when the SoC/CPU supports it (for example Intel QuickSync, and even Raspberry Pis !).

The SoC of Uno4K is a Broadcom BCM7252S, which as communicated by Broadcom can do "Dual HD AVC encode" (source : https://www.prnewswire.com/news-releases/broadcom-debuts-multi-standard-ultra-hd-chip-family-300016201.html )

Gstreamer talks to this SoC and uses its hardware encoding capabilities to do a fast HD encode (in this case in OpenVIX : 1280x720p at 29.97 Hz), while keeping its CPU usage close to 0% (as seen via the "top" command in ssh). I cannot find a proper documentation for this Soc which enlists all its supported resolutions and framerates for decoding and encoding. That would solve all this mystery !

[Trial]

Hi,
this is one problem with Broadcom, the maker of these SOCs, there is hardly any free documentation of their chips:-( Because there is no real reason o artificially limit the features of the chip I am quite sure that it is a hardware limitation.

ciao

[twol]

Agree with trial, finding what these Broadcom SOC'S do, is like looking for gold dust.
e.g. When you look at the initial ATV multiboot code for the HD51, they talk about what the chip can do differently when you change the bootmode and the information must have come to OpenATV from Mut@nt and originally from Broadcom - but I guess therefore only the receiver manufacturers see it.