search for sync token

[faljse]

Modified from #85 discussion
Works for me :)

[faljse]

Sometimes locks up at: https://github.com/phoboslab/jsmpeg/blob/master/src/mpeg1.js#L749
Edit:
Problem seems to be:

• 0x47 is detected somewhere in data stream, not being a sync token
• loop mentioned above is unlikely to hit exit condition in random data

Is there a more reliable way to detect sync tokens?
(Couldn`t find checksum in mpeg-ts header)

[phoboslab]

After a bit of digging, MPEG-TS seems to dictate that to find synchronization, you have to detect 5 consecutive 0x47 sync tokens with a distance of 188 bytes each. I.e. if you find a sync token, repeat to check byteIndex+187 for 0x47 4 times.

So if the streams looses sync, it's best to wait until the TS parser has at least 6 * 188 bytes buffered to scan through. Then scan through the first 188 bytes for the first token and jump +187 bytes each to find the next 4.

See for example: https://linuxtv.org/wiki/index.php/MPEG-2_Frame_Aligner

[faljse]

Done :)
I did quite a bit of testing today, and it works pretty reliable.

It might be a good idea to add some error recovery for things like the while(true) in decodeBlock()
(Maybe throw an exception and resync if we read() beyond the buffer in BitBuffer).
But for now this works well enough for me.

[phoboslab]

Thanks!