160 AAC audio file into OBS/twitch - will it be transcoded?

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ninjagaijin

New Member
Hi, I have a pre-recorded video I was going to play on twitch through OBS. It has 160 AAC audio. I believe I set up Core Audio encoder for OBS. When capturing this video either through a media source or window capture, should I expect a lossy transcode of the 160 kbps audio data?

The file is, I believe, core audio already..
Format : AAC LC
Format/Info : Advanced Audio Codec Low Complexity
Codec ID : mp4a-40-2
Title : Core Media Audio / simple_aac

Is there any way to 'pass through' the already compressed audio to avoid lossy transcoding? Or will re-encoding/transcoding to the exact same format and same bitrate just end up copying the current 160kbps data without additional layers of lossy transcoding compression?

I am running a music event and this is the first lossy audio I've come across so just wanted to learn what will happen
 
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ninjagaijin

New Member
TryHD said:
it will be lossy, use ffmpeg for prerecorded video streaming
Click to expand...

Do you mean for output settings in OBS, to use advanced output mode, with streaming setting: encoder: NVIDIA NVENC H.265/AVC (via FFMPEG) instead of NVIDIA NVENC H.265 (new) video encoder?
If 'via FFMPEG' is the one I want, what settings would you recommend to use?

Or are these the FFMPEG encoders in StreamFX plugin? I have this installed but not sure how to use.

Also I am not concerned with the video quality, but only with the audio quality - does FFMPEG still apply here?
 
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ninjagaijin

New Member
Or do you mean this audio FFMPEG plugin https://obsproject.com/forum/resources/ffmpeg-audio-filters-for-obs-studio.1126/ ?

To explain a little further, I am running a twitch 'music festival/event'. I add artists as authorised streamers so they can stream direct to twitch. I will also be performing myself. I have advanced custom output set for lossless audio recording with custom ffmpeg, but not sure how to set up ffmpeg properly for streaming settings. I have only one act with a pre-recorded video I want to play, which has only lossy 160 core/AAC audio in it. Just want to 'pass through' that audio without re-encoding preferably for stream. Recording for this video doesn't matter since it is already pre-recorded, I just need to stream it without lossy transcoding if possible.

I can create multiple profiles for different settings as it is not a problem for me to stop and re-start streaming between playing the pre-recorded video and then performing live on webcam and audio interface/capture. But ideally I would have the same settings for my live stream of lossless audio as well as for playback of the lossy audio in the pre-recorded video.

Probably not a huge deal since AAC isn't that bad at transcoding (from my experiences uploading 320 CBR AAC to mixcloud and having a 60-90 vbr AAC pop out that still sounds ok) but I would like to avoid lossy transcoding where possible. Wish the artist hadn't deleted his lossless source file lol.

edit: https://www.youtube.com/watch?v=kb_5_9GkwZc this video seems to suggest using ffmpeg to play pre-recorded videos 'faked as a livestream' but not sure how to set it up exactly
 
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ninjagaijin

New Member
So I figured out how to stream a pre-recorded video with ffmpeg command alone, but this now means no chat overlay, no logo etc.
So will have to use OBS still. Is there any way to play the pre-recorded video, with chat and logo overlay, without re-encoding the audio?
 
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