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clarification regarding VideoPlaybackQuality / droppedVideoFrames

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Nimesh Chanchani

Apr 12, 2022, 3:50:39 AM4/12/22
Hi Folks,

I'm implementing a Playback engine , and i'm required to implement :

interface VideoPlaybackQuality {
readonly attribute DOMHighResTimeStamp creationTime;
readonly attribute unsigned long droppedVideoFrames;
readonly attribute unsigned long totalVideoFrames;

The Documentation mentions :
The droppedVideoFrames attribute MUST return the total number of frames dropped predecode or dropped because the frame missed its display deadline.

My Concern and clarification is that :
- When starting playback and while repositioning we Syncronize Audio / Video . During this time the audio / Vide playlists are not syncronized ( The Audio is generally ahead of Video ) and starting Video frames have to be dropped to sync it with Audio track.

Should these dropped frames be accounted in render/ dropped statistics?

Secondly, While doing Trick playback , should dropped / rendered frames be added to the Stats?

As an example consider this use case:
1. Playback Starts
2. The IDR frame of the Video playlist is at Presentation timestamp , say "35.23"
3. The Audio Playlist is at presenation timestamp : "37.56"
4. Video frames from 35.23 to 37.56 will need to be dropped to syncronize with audio track.

Question: Should these frames be accounted in playback statistics? As this is just initial AV Syncronization , and is not reflective of playback quality. I would expect frames dropped after playback starts to be reflective of playback quality.

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