In our previous post (Analysis of LG U+'s HDTV Streaming (LG U+ HDTV Service based on LTE-A), we discussed how LG U+ Mobile U+ HDTV service delivers video files to a device. Our first actual measurement confirmed that LG U+:

• used HLS, Apple's adaptive streaming (delivering video files chunkwise, unlike progressive download or RTMP/RTSP); and  
• offered three profiles (quality levels).

Unfortunately, however, we could not confirm whether or not adaptive streaming (ABR Streaming) was actually utilized and thus the video quality was automatically adjusted based on the network conditions (Adaptive streaming is designed to automatically adjust the quality of a video to a higher or lower level depending on the quality level available in the network, ensuring uninterrupted video viewing experiences to users).   
 
However, during our actual measurement, we finally saw adaptive streaming actually being utilized (it was my first time to witness adaptive streaming actually working and adjusting the video quality automatically in Korea). Today, we will look further into how LG U+ implemented this adaptive streaming.  

The following video was accessed from a Samsung Galaxy 4 device (LTE-A) using LG U+ HDTV service over LG U+ LTE network. And it shows how the video quality is adjusted automatically as the network conditions changed.   

First, the video was in high-definition for about 14 seconds and then switched into a lower level with significantly degraded quality. What we should note here is that the video, though in degraded quality, was played with no buffering or interruption. So, we experienced degradation of the quality, but no buffering.  
 

Video captured in actual measurement
 

LG U+ HDTV Adaptive Streaming: Playlist (3 Profiles)
 
As discussed in the previous post (Analysis of LG U+'s HDTV Streaming (LG U+ HDTV Service based on LTE-A)), LG U+ HDTV service uses HLS, an Apple's adaptive streaming protocol, and provides 3 different profiles (quality levels) per video content. The following figure is a captured image of the LG U+ HDTV's playlist file. We can see 3 profiles (Playlist.m3u8) in each channel, and their quality levels (encoding rates) are marked as 1.5 Mbps, 1 Mbps and 500 Kbps, respectively.  

Playlist created for adaptive bit rate 

Bit Rate Switching Observed while Reviewing the Profiles of the Chunks Requested by a Device 
 
In order to check whether or not the video quality auto-adjusts in the real LG U+ commercial network, we intentionally changed the radio environment where the device (Galaxy G4) communicates and observed whether or not the device requested different profiles for each chunk depending on the network conditions.
 
After analyzing the chunk request messages (HTTP GET) of the packets actually measured, it was confirmed that the chunk with the highest quality (profile 50101, 1.5 Mbps) was requested and downloaded when the device was capable of downloading the chunk at 3 Mbps or higher. And the ones with the intermediate quality (profile 50102, 1 Mbps) and with the lowest quality (profile 50103, 500 Kbps) were requested and downloaded when capable of downloading at about 2 Mbps and at 1 Mbps or lower, respectively.

In the playlist, the encoding rates of each profile were marked as 1.5 Mbps, 1 Mbps and 500 Kbps. However, the actual analysis of each profile media file (.ts file) found the resulting actual encoding rates (bit rates) were about 20~30% higher than the levels marked in the playlist. 
 

The actual mediainfo measured is attached as Appendix at the end of this post.  
 
Adaptive Bit Rate Traffic Analysis
 
The figure below illustrates how chunks were requested and downloaded as the radio environment was changed, as captured by Wireshark in case of a full view. 

• Initial Buffering State: The device made a back-to-back request for the first 3 chunks (3 requests in a row) and filled the receiving buffer with the downloaded chunks immediately. 
• Steady State: Thereafter, it made a request for a chunk every 6 seconds and had the chunk downloaded. 
• The quality level of the chunks that the device requested has changed (1.5 Mbps -> 1 Mbps -> 500 Kbps) as the device's radio environment was changed. 

We can see the device switching to appropriate quality levels as the radio environment has changed so that the media service can be provided without delay or buffering.  
 

Mobile Video Service and Adaptive Streaming
 
Through our measurement of the three profiles defined in the playlist (manifest) file, we have witnessed actual adaptive bit rate switching taking place in changing network conditions. Based on our finding, we believe it was the first ABR supported in mobile devices successfully provided by a Korean mobile video service provider. Other than LG U+ HDTV, similar services have been offered by other Korean providers, but at a single quality level set by an operator or manually selected by a user. 

Most of Korean mobile video service providers are expected to join LG U+ in the ABR race sooner or later. 

 
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<Appendix>
 
High quality (Profile 50101)

Intermediate quality (Profile 50102)

 
 
Low quality (Profile 50103)