[Gnash-commit] [bug #45722] Gnash emitted loud screech after playing PCM audio object

[Nutchanon Wetchasit]

Follow-up Comment #10, bug #45722 (project gnash):

For stereo cases (`pcmplay-stereo.swf`):

The problem is similar to normal ones: decoder, both FFmpeg and GStreamer,
seemed to consume 65535 bytes which is not rounded to frame boundary.

Symptiom difference (FFmpeg V.S. GStreamer) is that GStreamer one seems to be
more straightforward; as the audio [fits Gnash's internal sample format],
it was passed verbatim without consideration of frame size,
and _tripped assertion error_.

Side note: I'm not sure if the assertion check [`assert(!(decodedDataSize%2))`
<http://git.savannah.gnu.org/cgit/gnash.git/tree/libsound/EmbedSoundInst.cpp?id=ba8ab1d9757bef44ab9be979072337a9e0fe463e#n118>
is correct, since Gnash's internal sample format seems to use 4 bytes/frame
not 2 bytes/frame.


For the double screeching (FFmpeg), I figured it was due to size of the
audio,
the misalignment started earlier, and covered the area where original
siren sound changes frequency, thus the screech changed into second pattern.

With second chunk ended before the end of sound, third `.decode()` call
resulted in a second misalignment; making the frame partially aligned again
(sample is aligned but _flipped channel_), this makes the final bits of
siren sounds apparently normal again.

Playing `pcmplay-lr.swf` (from the attached `pcmplay-lr.zip`) under Gnash
using FFmpeg backend will show the symptom of flipped channel
after the second screech.

(file #34835)
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Additional Item Attachment:

File name: pcmplay-lr.zip                 Size:290 KB


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