897486 - RTSP: investigate the impact of rtsp data discarding on I-Frames and media decoding

Status: RESOLVED WONTFIX

(Firefox OS Graveyard :: RTSP, defect)

Description

[Benjamin Chen [:bechen]]

This bug is forked from bug 831645 comment 104.

As we know, the RTSP is a network stream and there is a "ring buffer" in the RtspMedaiResource. The data may loss due to
1. The data rate comes from network is faster than decoder, so we need to overwrite some data because the ring buffer is full.
2. RTP packet loss/malformed.

In these cases, we want to investigate what happened if we loss the I-Frame.

In my thought, we can detect I-Frame at AVCAssembler/MPEG4ElementaryAssembler and pass the I-Frame info to RtspMedaiResource.
Regarding the RTP packet loss/malformed, we can also notify the RtspMedaiResource but seems useless because we don't know the type miss frame.

Or we can study the codec(H263/H264) to see if there exist a default behavior if I-Frame is missing.

Comment 1

[Chiajung Hung [:chiajung]]

Basically, I-frame is the base frame for motion vetor, any data loss in I-frame should cause damaged frame. If the whole frame got lost, the video will decoded incorrectly unless the scene is rather static untill next I-frame comes.

Comment 2

[Benjamin Chen [:bechen]]

Since we suspect the video quality is bad(or some corrupt frames) after pause/play,
we can try to detect H264 iframe first then observe the RTSP server behavior in pause/play.

http://stackoverflow.com/questions/1957427/detect-mpeg4-h264-i-frame-idr-in-rtp-stream