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Old 11-19-2013, 12:43 PM   #1
moyekj
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More detailed HLS statistics

Today I was testing Roamio Pro internal Stream downloads and monitoring things closely. Here's statistics I collected on the HLS downloads at different qualities:

BASIC QUALITY --> iPad
Show source: 60 min 1080i recording
Output: 544x400 @ 800 Kbps
Transfer time: 35 mins
File size = 393 MB
Total # HLS segments: 720

=>559 KB per segment (393MB*1024/720)
=> 5 seconds of video per segment

MEDIUM QUALITY --> iPad
Show source: 60 min 1080i recording
Output: 960x540 @ 1.24 Mbps
Transfer time: 35 mins
File size = 625 MB
Total # HLS segments: 1800

=>356 KB per segment (625MB*1024/1800)
=> 2 seconds of video per segment

HIGH QUALITY --> iPad
Show source: 60 min 1080i recording
Output: 1280x720 @ 2.24 Mbps
Transfer time: 37 mins
File size = 1075 MB
Total # HLS segments: 1800

=>612 KB per segment (1075MB*1024/1800)
=> 2 seconds of video per segment

NOTE: In home streaming encoding from Stream is equivalent to HIGH quality download.
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Last edited by moyekj : 12-01-2013 at 03:21 PM.
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Old 11-19-2013, 02:03 PM   #2
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2 second segments make sense for 8 second replay and 30 second skip to work. If the segments were 10 seconds long and you did an 8 second reply say 5 seconds into a 10 second segment it would have to either jump back only 5 seconds to the beginning of that segment or back 15 seconds to the beginning of the previous segment. Same applies to 30 second skip. With 2 second segments they can hit the exact time +/- 1 second.
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Old 11-19-2013, 03:27 PM   #3
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Good point about 8 second jump back - I never use that on the iOS App so forgot it was even there. Makes sense to be a multiple of both 8 and 30 seconds.
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Old 11-20-2013, 02:59 AM   #4
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Quote:
Originally Posted by moyekj View Post
I was surprised to see the 2 seconds per segment number as I expected it to be higher (around 10 seconds or so).
Why?
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Old 11-20-2013, 12:01 PM   #5
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Quote:
Originally Posted by MikePA1 View Post
Why?
Because the shorter the segments, the higher the number of references in the .m3u8 index file, which means higher overhead during playback. Plus most descriptions of HLS give 10 seconds as a typical segment length. In this case though the references are to local files on the iDevice instead of http references, so higher number of references is not really an issue because there should be very low latency in accessing the files. For WAN references likely the 2 second segments would present a problem.
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Old 11-21-2013, 12:24 AM   #6
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I updated stats with BASIC and HIGH downloads. I guess the theory of segment lengths evenly divisible into 8 and 30 seconds doesn't hold since BASIC is using 5 secs/segment.
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Old 11-21-2013, 12:58 PM   #7
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That's probably because of GOP length. To really compress H.264 you have to increase the GOP length, but with HLS each segment has to be a new GOP so that you can enter at any segment and start playing. This was likely a compromise. With 5 second segments they can still get close to both 8 and 30 seconds (+/- 2.5 seconds) while getting a higher level of compression.
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Old 11-26-2013, 05:51 PM   #8
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Hey guys, just got pointed to this thread by moyekj. I'm an old-time TiVo user who is considering coming back to the fold. I've been using Windows Media Center for a while and have played around with Plex. With Plex Media Server running on my Windows 7 box (Intel i7) I can stream to my iOS devices and get amazing quality for my Blu-ray rips or recorded HD TV shows. Plex offers a wide range of PQ bitrate options, all the way up to 1920x1080 @ 20 Mbps, though I'm not sure if it runs reliably (e.g., no pauses) at that high of a quality.

I just tried one of Plex's 1280x720 @ 3 Mbps and 1024x768 @ 2 Mbps options, and both looked fine on my iPhone 5, but my iPad retina's battery is currently dead, so I can't test it out there. I also didn't bother testing using AirPlay to send those options to my Apple TV, since the TiVo app doesn't support that anyway, so no use comparing how good/bad that bitrate looks when blown up on a large display.

Anyway, if any of you have first-hand experience using the Plex mobile app or AirVideo (a similar server-side/iOS combo), I'd be very interested to hear how you think the PQ, smoothness, and overall experience (e.g., hopefully free of stuttering/pausing) of the TiVo iOS app compares to those other solutions.

In case you're wondering why I'm thinking of coming back to TiVo, there are a few reasons, but as it pertains to this particular discussion topic, while the Plex app offers great PQ and AirPlay support, it doesn't support live TV playback and the Plex Media Server (server-side component) doesn't natively support the Windows Media Center TV show metadata, so you pretty much have to let a show record completely, then wait for another script/app rename the files into a Plex-friendly format, and then wait for Plex Media Server to re-pull the metadata online, before you can watch anything.
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Old 11-26-2013, 06:04 PM   #9
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One thing to keep in mind is that using Stream is not the only way to get videos from TiVo onto your iDevice. There's the traditional TiVo To Go mechanism where for non copy-protected recordings on the TiVo you can download as recorded and then you can re-encode to play on an iDevice at whatever quality level you choose. The Stream is just a quicker, more convenient way to do things, but you are stuck with preset quality levels and inability to do any editing of the recorded video (like say to remove commercials).
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