Everything transcoding..?

[soniCron 5]

Practically everything H264 to my FireTV (2nd gen) with official Emby app transcodes with the following reason:

Info App: Profile: VideoCodecProfile, DirectPlay=false. Reason=Android-VLC.RefFrames Condition: GreaterThanEqual. ConditionValue: 2. IsRequired: False.

...except all the videos have ref frames of 1. Playing to Android phones and tablets works direct; no transcoding. Kodi on FireTV streams direct as well.

 

These are H264/AAC compliant streams in MP4 containers, fwiw...

 

Bug? Or "feature"..?

[Luke 42077]

Hi there, we're very sorry to hear about this. In order for us to best help you, please discuss some specific playback sessions and make sure to provide the information requested in how to report a media playback issue. Thanks !

[ebr 16169]

Hi. This is an issue only in mp4 containers right now because we've had numerous reports of mp4s with only one ref frame playing back with no video.

 

We need to somehow figure out how to tell which ones will play properly and which won't.

 

As an aside, did the item play back okay or was there a problem?

[soniCron 5]

The transcode played okay, yes. (Just ugly-ish)

 

Actually, on the note of transcoding... since high efficiency codecs (h265, vp9, etc) are roughly twice as efficient as h264, doesn't it make sense to cap their transcode bitrate at double the h265/vp9 bitrate? I only ask cuz it seems that when transcoding, it decides not to ever go above the bitrate of the original file, but that doesn't always make sense with lower-bitrate encodes, and especially not with high efficiency encodes.

 

Just a thought.

Thanks!

Edited November 28, 2016 by soniCron

[ebr 16169]

The bitrate of the source is a real limit.  We cannot create bits that aren't there .

 

Okay, I guess we could attempt some sort of upscaling but this would take even more processor power and not really be practical.

[soniCron 5]

Right, but... it's about minimizing damage. We're talking about recompressing with a lossy format, and further, not all codecs are created equal. Visually speaking, h265 and VP9 use about half the bits to encode the same scene as would be encoded with h264, for example. Upscaling isn't necessary to benefit from transcoding at a higher bitrate than the source, especially when the source is a high efficiency codec.

 

Loss of data on top of lost of data = more loss of data. The less data lost during the transcode, the closer to the original quality. At high bitrates, it doesn't really matter. At lower bitrates (especially depending on the codec), it can make a substantial difference if the bitrate is capped to the source's bitrate.

 

The "value" of a bit in an h265 or VP9 encode is substantially higher than that of a bit in an h264 encode. You obviously cannot create bits that aren't there, but the reconstructed stream of h265/VP9 is of higher fidelity than that same stream at the same bitrate encoded with h264.

 

Therefore... high efficiency codecs should be transcoded at a higher bitrate (as long as h264 is the target transcode codec), otherwise data is being thrown away to the detriment of visual quality.

 

Just a thought...

[Luke 42077]

We do make that type of bitrate adjustment when converting from h265 to h264. I will check and make sure it is also applied with VP9. Thanks.