Blotches appearing on H264 / MPEG4 AVC videos in VLC

[PeaShooter_OMO]

Good day

I have quite a few H264 / MPEG4 AVC video files that will show this anomaly in VLC where always at the same places in the video regularly repeating, blotches will appear against a background area of generally the same colour. In other words; blotches usually lighter than the background on which they appear. And the backgrounds on which they appear will usually be of the same gradient of colour, for instance a wall in a room and usually it will happen more (or I will notice it easier) on backgrounds with darker colours. The blotches appear slowly and very subtly and then become more prominent, then suddenly disappear. This all happens in a matter of seconds, then start to repeat a few seconds later. You can close the video file and VLC and open it again and go to the exact time where you saw it appear and they will again appear exactly in the very same manner that they did in the previous session.

I have tested the same video files on Windows XP SP2 and Windows 7 SP1 and the blotches are exactly the same. I have also tested it on different VLC versions starting from 2.0.6 going down at different version releases and they all do it except for version 1.0.5. I have not tested it on an earlier version than 1.0.5. The next version up from there which I tested was 1.1.3 and that also had the blotches. I also tried different output methods (DirectX, OpenGL) but both had the blotches. I also tried two different NVidia drivers and both had the issue.

I then tried MPC-HC and that did not have the blotches

I then tried it on another PC with WinXP and that machine also had the blotches.

My PC has a NVidia 250GTS and the other PC has a NVidia 5500 screen card

Please have a look at the attached screenshot of the blotches in VLC and a screenshot of the same video in MPC-HC which did not have the blotches.





Is there a setting which will stop this from happening or is this a VLC issue?

Thank you for your time

[Baldrick]

Probably a VLC issue.

I would also post this in the official VLC forum.

[PeaShooter_OMO]

I have done that and have not received any suggestions yet. That's why I tried this forum to see if someone here might have an idea.

[Selur]

Does it change in MPC-HC if another Renderer is used? (try all the renderers, if one or multiple of them show the same blocking one could inform the VLC guys)

[PeaShooter_OMO]

Yesterday I also tried a friend's PC with the same video files. It also produces the blotches. He also has a NVidia screen card. I will test MPC with different renderers.

[PeaShooter_OMO]

I have tested with MPC-HC and all its different renderers and none of them produces the blotches

[Selur]

Okay, so the problem isn't related to the renderer.
Next thing that probably differs between VLC and MPC-HC is the used decoder.
VLC and MPC-HC both come with their own decoders.
VLC uses libav and MPC-HC 1st tries to use a dxva hardware accelerated decoder and then uses the system direct show decoder.
-> try if it changed something if you change in example the 'H264 skip delocking mode', ' Error resilience', 'IDCT Algorithm' inside the H264/AVC (DXVA) video decoder configuration inside MPC-HC.

Cu Selur

[PeaShooter_OMO]

I have tried the different settings that you mentioned and still it seems that MPC-HC decodes the video file fine. No blotches.

I wonder if I should report a bug at VLC.

[Selur]

Since all H.264 Decoders should output the same content (aside from custom post processing) this really looks like a bug.

Cu Selur

[PeaShooter_OMO]

I really think so seeing that in VLC version 1.0.5 it didn't have the blotches. I will report a bug.

Thank you so much for your suggestions.

[fvisagie]

I really think so seeing that in VLC version 1.0.5 it didn't have the blotches. I will report a bug.

Thank you so much for your suggestions.

If you want to make doubly sure, post a sample clip for comparison on others' VLC installations.

Cheers,
Francois

[PeaShooter_OMO]

I uploaded the following sample.

http://files.videohelp.com/u/221742/vlc-record.mp4

It is part of one of the video files which produces the blotches. Keep an eye on the bottom-left-hand corner. While the actors walk down the ramp you will see (or so I hope) the blotches starting to appear on the dark area of the ramp.

Dankie Francois

[fvisagie]

Interesting results I got from that test clip, and it helped me solve a problem I never realised I had!

With Windows Media Player I got no blotches. According to graphedt it likely was using the Nokia H264Dec HP/MP Filter. That is the only system H264 filter - disabling it causes H264 playback to fail.

With MPC-HC 1.6.3.5818 (2320902) I got blotches. It was configured to use its own internal filters.

With MPC-HC, I could get rid of the blotches by disabling DXVA in any of the following ways:

• Changing to a renderer that does not support DXVA
• Disabling the MP4/MOV internal source filter (but then there's no sound)
• Disabling the H264/AVC (DXVA) internal transform filter

MPC-HC blotches; MPC-HC H264/AVC (DXVA) disabled

When diabling H264/AVC (DXVA), the remaining H264/AVC (FFmpeg) filter is then used instead. I could confirm that by setting its H264 skip deblocking mode to All frames, which reintroduced the blotches. Confusingly, the H264/AVC (DXVA) property dialog is identical to that of H264/AVC (FFmpeg), i.e. the latter also has the same DXVA settings. However, it doesn't seem to use DXVA as there's no mention of it on the status bar when using that filter.

So, what this tells me is that potentially your problem can also be caused by renderer/DXVA/decoder/decoder configuration (i.e. deblocking) settings. Unfortunately I'm not familiar with VLC at all and can't suggest where to look, but hopefully these findings give you something to work with.


Cheers,
Francois

[PeaShooter_OMO]

It seems that VLC uses FFmpeg by default. Please correct me if I am wrong. And in VLC's FFmpeg deblocking is set to None by default. If I change it to any other setting it stays the same or makes the blotches worse.

[fvisagie]

Any chance of disabling DXVA?

Failing all else, you may have to consider changing your player.

Cheers,
Francois