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Interlaced MP4 Recording cuts the resolution by half(?)
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Joined: 6/4/2016(UTC) Posts: 14  Location: Warsaw, Poland Thanks: 2 times
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I've been using the Recording feature to record 480i50 videos through the builtin MP4 option. I noticed that my videos are very pixelated but such thing does not happen when FFmpeg is used instead. So I decided to do a comparison. I set a higher recording bitrate (8Mbps), placed a sample logo on the overlay and played a sample video. Here are the results: MP4 Recording frame : SettingsFFmpeg Recording frame : SettingsYou can clearly see on the grabbed frames that when recording with MP4 the main text from the video is pixelated and the logo is barely readable, however the video from FFmpeg looks clean and not pixelated at all. This pixelation is visible on higher resolutions like 1080i50 too. It looks a bit like the resolution was somehow cut by half. It does not occur when recording progressive. I would switch to using FFmpeg but I need bitrate as low as 1Mbps which is only supported through MP4 option. Thanks for any help in sorting this out.
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Joined: 3/20/2014(UTC) Posts: 2,721  Location: Bordeaux, France Thanks: 243 times
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Hi
I previously understood your recordings were for archiving purposes. Can you explain what is the motivation for doing interlaced recordings?
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Joined: 1/13/2010(UTC) Posts: 5,211 Location: Gold Coast, Australia Was thanked: 4301 time(s) in 1523 post(s)
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MP4 recording in vMix does not support interlaced so it needs to deinterlace it prior to recording which is why it looks the way it does.
Interlaced doesn't record well at low bitrates anyway so I would suggest changing your master frame rate to 25p for the best quality.
Regards,
Martin
vMix
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 1 user thanked admin for this useful post.
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Rank: Member
Groups: Registered
Joined: 6/4/2016(UTC) Posts: 14 Location: Warsaw, Poland Thanks: 2 times
Was thanked: 3 time(s) in 3 post(s)
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@DWAM: The main reason is to preserve original frame rate as we are doing all production in 1080i50. For high quality recording we use HyperDecks and other dedicated recorders in our workflow but additionally we are obliged to record and store everything our channel broadcasts 24/7 (vMix serves as our main broadcast server). Scaling down to 480i has downsides but the quality would be totally fine for us (except the problem that this topic is about).
@admin: Thank you for clarification. I will have to switch to 25p or to FFmpeg then.
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Rank: Advanced Member
Groups: Registered
Joined: 3/20/2014(UTC) Posts: 2,721 Location: Bordeaux, France Thanks: 243 times
Was thanked: 794 time(s) in 589 post(s)
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OK. I understand better now if you are TV broadcaster.
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Rank: Advanced Member
Groups: Registered
Joined: 3/20/2014(UTC) Posts: 2,721 Location: Bordeaux, France Thanks: 243 times
Was thanked: 794 time(s) in 589 post(s)
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For this 1Mbit recording preset you are missing, you can use EXTERNAL out to feed FFMPEG with vMix virtual devices (video and audio).
This way you can use your own recording settings. I do this for special recordings sometimes: the idea is to create a batch file that simply needs to be executed to start recording (and CTRL+C to stop)
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1 user thanked DWAM for this useful post.
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