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Always send PictureID 0 in VP8Payloader - #376
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With EnablePictureID, the frame whose PictureID is 0 was sent without the X and I bits, so it carried no PictureID at all. The ID wraps every 32768 frames (9 min 6 s at 60 fps), so a long stream had one frame without a PictureID among frames that had one. Chrome then lost the frame references and dropped every frame until the next keyframe: a freeze every 546 s, with no lost packets, NACKs or PLIs. Frame 0 now carries a 7-bit PictureID like every other ID under 128.
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #376 +/- ##
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+ Coverage 87.45% 87.48% +0.02%
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Files 28 28
Lines 3173 3172 -1
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Hits 2775 2775
+ Misses 398 397 -1
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Description
With
EnablePictureID,VP8Payloadersends the frame whose PictureID is 0 without the X and I bits, so that frame carries no PictureID (case p.pictureID == 0:keeps the bare 1-byte descriptor). The ID wraps to 0 every 32768 frames, so any stream longer than that has one frame without a PictureID among thousands that have one.Chrome then loses the frame references and drops every frame until the next keyframe. At 60 fps this is a freeze every 546 s (9 min 6 s), with no lost packets, no NACKs and no PLIs. Its length depends on how far the next keyframe is: with a keyframe every 180 frames, 32768 = 182 × 180 + 8, so each freeze was 8 frames (~133 ms) shorter than the one before.
We found it in a game-streaming app built on Pion (
TrackLocalStaticSample+ VP8). The browser'sinbound-rtpstats showedframesReceiveddropping to 17-24 per second for under a second at exactly every 546 s, while the sender kept 60 fps. The predicted times matched to the second (three in a row), and the freezes were gone after sending a PictureID on every frame (two hours, 443,928 frames, 13 wraps, no freezes).This change sends frame 0 with a 7-bit PictureID, like every other ID under 128. The new
WithPictureID_wraptest fails without it (frame 0 comes out as{0x10, 0x91, 0x91}).