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

[Nutchanon Wetchasit]

Follow-up Comment #9, bug #45722 (project gnash):

>From the attached `pcmplay_gnash0.8.11dev-dc51f53_diagnostic.zip`.

This is an exerpt from output on playing `pcmplay.swf` using FFmpeg backend:

DEBUG: AudioDecoderFfmpeg: initialized FFmpeg codec 65536 (pcm_s16le) for
flash codec 3 (Uncompressed)
DEBUG:   decoding 65535 bytes (offset 0, remaining 88200, total 88200)
DEBUG:   decoded to 131028 bytes, used 65535 bytes from source
DEBUG:   decoding 22665 bytes (offset 65535, remaining 22665, total 88200)
DEBUG:   decoded to 45328 bytes, used 22665 bytes from source


(The second set of `decoding ... decoded ...` output is emitted the same time
as screech sound)

>From `used 65535 bytes from source` part, it shown that the underlying
decoder
consumed audio data in a block that's *not aligned to frame boundary*.
(PCM 16-bit Mono has frame size of 2 bytes) This has potential of messing up
the subsequent read; which is evident as the second `.decode()` call was
occured at the same moment that screech is audible.

This is an exerpt from output on playing `pcmplay.swf` using GStreamer
backend:

DEBUG: AudioDecoderSimple: initialized flash codec 3 (Uncompressed)
DEBUG:   decoding 65535 bytes (offset 0, remaining 88200, total 88200)
DEBUG:   decoded to 131068 bytes, used 65535 bytes from source
DEBUG:   decoding 22665 bytes (offset 65535, remaining 22665, total 88200)
DEBUG:   decoded to 45328 bytes, used 22665 bytes from source


(The second set of `decoding ... decoded ...` output is emitted the same time
as screech sound)

Problem _is the same_ as FFmpeg (`used 65535 bytes from source`), only
difference are decoded sizes of data; GStreamer backend seems to be
more accurate on this; there is 65534 bytes worth of complete frames
on first read, which output data is correctly shown as 131068 bytes.

Note (for the record): As far as I know, Gnash's sound decoding process
always
convert sample format to PCM 44100 Hz 16-bit stereo (4-byte/frame).

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