T4 - Jerky Playback

stevebow · Post by **stevebow** » Tue Jan 30, 2024 14:36

I am using Handbrake to convert H.265 material to H.264, needing to do this more and more nowadays as the usual "sourced" material tends to be more and more H.265.

In all the countless hours of H.264 material I have viewed on my T4, I have not seen the following problem before. In any episode of a series I have converted to H.264, while everything generally plays fine, every 5-10 mins a particular shot i.e. between 2 cuts, will become jerky. After a cut to something else, playback is fine again.

The H.264 conversions I do in Handbrake are always using the NVENC encoder (a GTX 1080 GPU), and I just use the default settings i.e. Encoder Preset = Medium, Encoder Profile/Level = Auto (which comes out as MAIN@L4). I have attached an example clip - watch what happens after the rail track is switched over and cuts to a man walking behind 2 others. On my T4 the video is noticeably jerky. Then a cut to horses in the distance, playback is normal again. Every now and then, a particular shot between 2 cuts, jerky playback only on that shot.

I've monitored the serial o/p from the T4, but nothing is logged when this occurs. Video playback is fine on the PC using VLC/PotPlayer/Media Player, so it seems to be a playback issue with the T4.

A few things I've experimented with. Adjusting the CQ value between 0 (min) and 51 (max) makes no difference. Using NVENC Encoder Presets Medium -> Slowest, same problem. However, using Fast -> Fastest actually fixes the problem, playback is entirely smooth.

If I don't use the NVENC encoder but instead the CPU H.264(x264) encoder, no problem, all good.

I suspected perhaps the bitrate on these affected shots was just a little high for the T4 to decode, but using the Fast -> Fastest encoder profiles results in a clip with higher bitrates - and they play fine(!). So I am a little stumped about this one. MediaInfo doesn't offer any clues either.

I'm not really too fussed because I just use the Fast encoder profile now, but I am curious nevertheless. Any ideas why the T4 struggles with this clip, anyone?

adoxa · Post by **adoxa** » Wed Jan 31, 2024 00:18

The T2 is not jerky, but it does slow down a bit (using slow motion does make it jerky, though); the V2 is fine. I didn't think to remux it, I'll try that tomorrow...

adoxa · Post by **adoxa** » Wed Jan 31, 2024 16:56

FWIW the remuxed MP4 & TS also exhibit the same problem on the T2; the V2 is still fine.

stevebow · Post by **stevebow** » Thu Feb 01, 2024 11:15

The actual shot itself does appear slowed down slightly, presumably done in post production. Or maybe it appears that way to me.

Unfortunately I don't have any mpeg analysis tools that would show things like GOP sequence, running bitrate, etc. ffprobe doesn't appear to show anything useful in this case either.

I guess you don't have a T4 or U4?

FWIW, I've attached the original H.265 material.

Paul_oz53 · Post by **Paul_oz53** » Thu Feb 01, 2024 12:35

The original clip is fine on my U4 but the transcoded version is jerky at about 9-15 secs on the U4 and T4.

adoxa · Post by **adoxa** » Thu Feb 01, 2024 17:20

As you'd expect the original has no video on the T2, the V2 is fine.

Remuxed the original MKV to TS and then used the V2 to transcode it and play that on the T2 - the start didn't really work until the switch, but that did seem fine.

As to the original question, no idea. There's nothing in the log indicating any change within the video itself. Maybe just chalk it up to one of those things...