Audio Transcode

[Michele Firmasyah]

Encodingis the process of compressing video and audio files to be compatible with a single target device. Transcoding, on the other hand, allows for already encoded data to be converted to another encoding format. This process is particularly useful when users use multiple target devices, such as different mobile phones and web browsers, that do not all support the same native formats or have limited storage capacity.

Encoding is a naturally lossy process, meaning that it causes a certain amount of data to be discarded and ultimately decreases audio and video quality. Encoding can use lossless compression, but it results in decreased compression rates and increased media file sizes.

Transcoding and encoding should not be confused with transmuxing which only converts the container format such as MP4 and FLV (Flash). On the other hand, video and audio files are compressed by codecs such as VP6 and H.264. However, similar to transmuxing, transcoding can be done using FFmpeg, a popular open source software designed to handle all video and audio formats. Converting any media to a standard H.264 mp4 can be done with a simple command:

The above command will take sourceVid.mov, which has already been compressed and encoded, decode it, and reformat it into an MP4 file using the H.264 codec. The resulting file will be named transcodedVid.mp4.

The above command takes an RTMP stream and encodes it using x264, a H.264 encoder. The additional options included in the command set the bitrate, buffer, framerate, and resolution of your output, which will be in an FLV (Flash) format.

Transcoding is a powerful process that is leveraged by major streaming organizations such as Twitch, which actually uses both FFmpeg and its own TwitchTranscoder to stream video and audio on its platform.

The reason it is transcoding is the Audio but assuming you are selecting the AC3 before you press play (which you have according to the log) - then I see no reason why you should not be able to direct play.

The attempt to direct play failed (as indicated in the transcode reasons) so we played it using transcoding. If you play the item for just a few seconds and then immediately send a log from the app, we can see why it failed.

ok thanks @ebr - so while the OP is sending theirs, I've just sent mine - User:Richard - FireTV transcodes to AAC - it doesn't seem to want to recognise AC3/EAC3 at all. All other clients OK, VLC plays it OK (via Emby) on the FireTV ok.

My third thought was it was playing for 80% of the film no issues then towards the end the audio cut out but the picture was fine, stopping and starting 3 times it eventually kicked in but then starting glitching and on review I was getting 1.1mbps transcode, hence this thread.

Hi ebr - thanks. Yes this an original Gen 2 FiretV stick - it always used to play AC3 and EAC3 just fine. It definitely supports AC3/EAC3 as other players work just fine. Amazon also reports it as fully capable - see

@ebr - Just to report that the release version of Emby on FireTV ( 2.0.09a) and the new emby release (4.6.0.50) are now playing AAC, AC3 and EAC3 perfectly (direct) - thanks for showing some love to the Gen2 sticks - which still perform very well imo and seem a little faster in the latest release.

When the video transcodes, either by setting the quality to "Auto" or to an intentionally low bitrate, the audio will also transcode and therefore play. "Auto" quality results in a video transcode consistently for them, though they don't have buffering issues when they manually set it high.

I personally also have an LG tv, and for me DTS audio will always transcode automatically regardless of if the video is direct playing or transcoding. I've double checked both their account and mine have all settings to allow transcoding enabled.

I found the thread below and the issue seems similar, but not the solution. I also use an nginx reverse proxy and have a 301 redirect, but the redirect isn't being used here. The user specifies https in the server address and port 443, so the redirect running on port 80 and with http shouldn't ever be hit. I also had already set the "secure connection mode" setting to "Handled by reverse proxy".

Can you please get them to check if it has the latest firmware (I think it should be 05.50.15 for that model)? Are they using the TV's speakers, or is it connected to a receiver? If it is through a receiver, is it via optical or HDMI/ARC connection - can they do a test with just the TV's speakers?

I have a video for which I'd like to convert the audio codec to AAC 320 kbps / 44.100 kHz. What would I use for ffmpeg switches such that all the video settings and codec remain the same, but only the audio codec and settings change?

Already using Amazon Elastic Transcoder? It's simple to migrate to MediaConvert. For more information, see this overview which includes valuable information about the migration process and links to additional resources.

Digital audio is stored, transferred, and played back as channels, and you can store, transfer, and play back multiple channels in tracks, also known as streams. Multiple channels and tracks allow you to include extra information such as surround sound, stereo, and multiple languages in files. For example, you can have a file with a surround sound track that has six channels and a stereo track with two channels. You can use Elastic Transcoder to change the number of tracks and channels in your file. If you have a file that has only a surround sound six-channel track, you can use Elastic Transcoder to create a file that has a stereo two-channel track.

A single channel carries the information played by a single speaker. For example, a stereo track with two channels sends one channel to the left speaker and the other channel to the right speaker. You can use tracks to choose between different sets of channels. For example, you can have a file with two tracks: one track with two channels, and one track with six channels. When your player plays that file, it can use the two-channel track for a stereo speaker system, or the six-channel track for a surround sound speaker system.

Not all tracks have audio information. Tracks without audio are known as Mit Out Sound (MOS) tracks. You can use MOS tracks and a sound editing program to add sound effects and music to your file. If your output file uses an MXF container, you can use Elastic Transcoder to add MOS tracks to your file.

Elastic Transcoder defaults to a single track, but lets you choose the number of channels in that track. You can choose up to two tracks, or pass through the same number of channels that your input has. If you transcode a file with an MXF container, Elastic Transcoder lets you create multiple tracks for your output.

Transcoding is the direct digital-to-digital conversion of one encoding to another,[1] such as for video data files, audio files (e.g., MP3, WAV), or character encoding (e.g., UTF-8, ISO/IEC 8859). This is usually done in cases where a target device (or workflow) does not support the format or has limited storage capacity that mandates a reduced file size,[2] or to convert incompatible or obsolete data to a better-supported or modern format.

In the analog video world, transcoding can be performed just while files are being searched, as well as for presentation. For example, Cineon and DPX files have been widely used as a common format for digital cinema, but the data size of a two-hour movie is about 8 terabytes (TB).[2] That large size can increase the cost and difficulty of handling movie files. However, transcoding into a JPEG2000 lossless format has better compression performance than other lossless coding technologies, and in many cases, JPEG2000 can compress images to half-size.[2]

Transcoding is commonly a lossy process, introducing generation loss; however, transcoding can be lossless if the output is either losslessly compressed or uncompressed.[2] The process of transcoding into a lossy format introduces varying degrees of generation loss, while the transcoding from lossy to lossless or uncompressed is technically a lossless conversion because no information is lost; however, when the conversion is irreversible, it is then more correctly known as destructive.

One can also use formats with bitrate peeling, that allow one to easily lower the bitrate without re-encoding, but quality is often lower than a re-encode. For example, in Vorbis bitrate peeling as of 2008, the quality is inferior to re-encoding.

The key drawback of transcoding in lossy formats is decreased quality. Compression artifacts are cumulative, so transcoding causes a progressive loss of quality with each successive generation, known as digital generation loss. For this reason, transcoding (in lossy formats) is generally discouraged unless unavoidable.

For users wanting to be able to re-encode audio into any format, and for digital audio editing, it is best to retain a master copy in a lossless format (such as FLAC, ALAC, TTA, WavPack, and others) that take around half the storage space needed when compared to original uncompressed PCM formats (such as WAV, and AIFF), as lossless formats usually have the added benefit of having meta data options, which are either completely missing or very limited in PCM formats. These lossless formats can be transcoded to PCM formats or transcoded directly from one lossless format to another lossless format, without any loss in quality. They can be transcoded into a lossy format, but these copies will then not be able to be transcoded into another format of any kind (PCM, lossless, or lossy) without a subsequent loss of quality.

For image editing users are advised to capture or save images in a raw or uncompressed format, and then edit a copy of that master version, only converting to lossy formats if smaller file sized images are needed for final distribution. As with audio, transcoding from lossy format to another format of any type will result in a loss of quality.

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