Understanding why Plex behaves the way it does - transcoding question

[Dravinian]

Apologies if this is not the right place, but figured, it is on a NAS, it is on a server, it may be a server setting that is effecting the behaviour, so ask in the NAS section.

 

I am trying to understand why Plex transcodes some files, but does not transcode other files.

 

The obvious answer is "input file is different to output file" but that doesn't appear to be the whole story.

 

I have a UHD file 2160p, I am sending to a 4k TV over the internet.  Plex transcodes it to 720p.  It is not a bandwidth setting, or a quality setting as I have set this to the maximum on both sending and receiving Plex.

 

In other cases, I have sent files as a 'Direct Stream' but I do not seem to have any control over this, and I can't see any reasons why Plex makes the decision on whether it is a Direct Stream or transcoded - as it is not quality, file settings, bandwidth etc.

 

Am I missing a setting that needs to be manipulated or is this just something done in the background over which I shall never have any control?

[Mayaa]

Could be a unsupported container or file format, or possibly subtitles.

If i remember correctly Tautulli displays why its transcoding something.

[Dravinian]

11 minutes ago, Mayaa said:

Could be a unsupported container or file format, or possibly subtitles.

If i remember correctly Tautulli displays why its transcoding something.

Cheers for the tip, just set up Tautulli on FreeNAS, will see if it provides me any extra information in relation to why it is behaving this way.

[WereCatf]

1 hour ago, Dravinian said:

 

I have a UHD file 2160p, I am sending to a 4k TV over the internet.  Plex transcodes it to 720p.  It is not a bandwidth setting, or a quality setting as I have set this to the maximum on both sending and receiving Plex.

 

In other cases, I have sent files as a 'Direct Stream' but I do not seem to have any control over this, and I can't see any reasons why Plex makes the decision on whether it is a Direct Stream or transcoded - as it is not quality, file settings, bandwidth etc.

 

Am I missing a setting that needs to be manipulated or is this just something done in the background over which I shall never have any control?

Often it is because the receiving device doesn't support the codecs in use. It can only direct-stream videos to devices which support both the audio- and video-codec at their current settings.

[Dravinian]

5 minutes ago, WereCatf said:

Often it is because the receiving device doesn't support the codecs in use. It can only direct-stream videos to devices which support both the audio- and video-codec at their current settings.

Yeah I think it is because my files are MKV which is not a supported file format, and I am unclear on whether the TV accepts MKV files or requires them in MP4.

it is something I will look at.

[WereCatf]

1 minute ago, Dravinian said:

Yeah I think it is because my files are MKV which is not a supported file format, and I am unclear on whether the TV accepts MKV files or requires them in MP4.

That's a different thing. MKV, MP4, AVI, MOV etc. are container-formats, whereas H.264, HEVC, AAC, DTS etc. are codecs. You'll to have check both the container-formats and the codecs that you use.

[brwainer]

Container format doesn’t matter for direct stream, just codec format. Plex has both Direct Stream (sending individual streams) and Direct Play (sending the whole container) and the client chooses what it wants based on its decode capabilities. Direct Stream/Play can also be disabled by subtitles depending on the subtitle format - most clients can show DVD or TV subtitles with Direct Show, but not Bluray or community made subtitles, because those are a more complicated format that allows a lot more customization.

[Thirdgen89GTA]

17 hours ago, WereCatf said:

Often it is because the receiving device doesn't support the codecs in use. It can only direct-stream videos to devices which support both the audio- and video-codec at their current settings.

Plex does it for a few reasons, including the ones you listed. 
 

it will also transcode based on whether it determines if the client is WAN or LAN. It supports basic detection of your upload bandwidth. 
 

in my Plex server preferences I listed my local Vlans so it doesn’t use the max upload bitrate I have set. 
 

Example ona Speedtest I can do about 30mbps. So I set max upload at 21mbps. Any stream over 21mbps streaming to a WAN client is forced to transcode. I also limited my server to 5 simultaneous transcodes with a max bitrate of 10mbps. 
 

this way I’m pretty assured I can handle two External clients at 10mbps 1080p. 

[Donut417]

On 6/25/2020 at 3:54 AM, Dravinian said:

Apologies if this is not the right place, but figured, it is on a NAS, it is on a server, it may be a server setting that is effecting the behaviour, so ask in the NAS section.

 

I am trying to understand why Plex transcodes some files, but does not transcode other files.

 

The obvious answer is "input file is different to output file" but that doesn't appear to be the whole story.

 

I have a UHD file 2160p, I am sending to a 4k TV over the internet.  Plex transcodes it to 720p.  It is not a bandwidth setting, or a quality setting as I have set this to the maximum on both sending and receiving Plex.

 

In other cases, I have sent files as a 'Direct Stream' but I do not seem to have any control over this, and I can't see any reasons why Plex makes the decision on whether it is a Direct Stream or transcoded - as it is not quality, file settings, bandwidth etc.

 

Am I missing a setting that needs to be manipulated or is this just something done in the background over which I shall never have any control?

Plex transcodes based on the support file formats of the device you're stream to. For example Live OTA TV is done in MPEG2. My parents Roku sticks don't do MPEG2, so my server transcodes the live TV to a format that the Roku sticks understand. Some times Plex might only need to transcode Video or Audio, but this is all based on what the streaming device supports. 

 

If you want to stop transcoding then I suggest you look at the formats each of your device support and hopefully find one format they all support, OR have the same video in several formats so devices can direct stream. 

[Jarsky]

Yeah codecs is typically the answer. 

 

Especially with audio. A lot of dvd/bluray content has some form of Dolby Digital audio. They're all licensed, so most TV's don't support Dolby. So you will almost always see dvd/bluray content in Dolby Digital, Dolby TrueHD, Dolby Atmos, etc...at the very least transcoding audio streams to something the TV can decode. 

 

As for video, it depends if its HEVC (h265), h264/x264, mpeg2, wmv, etc....and what formats your TV support. As pointed out above, containers != codecs.

[Kobach23]

Another thing to consider is can your internet handle streaming 4K? I'm on Spectrum with 200mb down / 10 mb up and I keep my Plex by default at 720p 4mb/s streams to try and allow multiple streams at once. I believe users can manually override this and select higher qualities but you might physically hit a limit with mid grade 1080p and not be able to stream higher.

 

I think enough other people have covered the codecs and file formats so I'm leaving that part out but I agree. Most media I have is .mkv and most devices in my experience (TVs, phones, tablets, etc) can't receive that so it has to be converted into something readable. Hope this helps.