When digitizing composite video from a analog videotape source using the
TVP5150's first composite input channel, the captured stream exhibits
tearing and synchronization problems[1].
It turns out that commit c0477ad9fe caused
"TV mode" (as opposed to "VCR mode" or "auto-detect") to be forcibly
enabled for both composite inputs. According to the chip
documentation[2], "TV mode" disables a "chrominance trap" input filter,
which appears to be necessary for high-quality video capture from an
analog videotape source. [ Commit
c7c0b34c27 subsequently restricted the
problem to the first composite input, apparently inadvertently. ]
Since any type of composite signal source can be connected to the
TVP5150's first composite input, unconditionally forcing "TV mode" isn't
correct. There doesn't appear to be a good way for applications to tell
the driver what is connected. Fortunately, the TVP5150 has an operating
mode auto-detection feature, which, when enabled, should cause the TVP5150
to auto-detect whether it should use "VCR mode" or "TV mode". Enabling
operating mode auto-detection improved video capture quality
significantly[3].
Therefore, fix this bug by using operating mode auto-detection. (Also,
while here, fix a CodingStyle issue.)
For those users who may find this patch via a mailing list archive but who
are not able to upgrade to a kernel with a fixed driver: the TVP5150's
S-Video and second composite input sources have auto-detection enabled, so
you may wish to try using those -- if available on your device -- until
this fix makes it a downstream distribution near you.
1. Pre-patch tvtime snapshot using a Pinnacle PCTV HD Pro as the
capture device and a Sony EV-S2000 as a video source:
http://www.booyaka.com/~paul/tvp5150/1a.png
2. Section 3.21.3, "Operation Mode Control Register", _TVP5150AM1
Ultralow-Power NTSC/PAL/SECAM Video Decoder (Rev. D)_ [SLES209D],
downloaded 8 October 2010, available via
http://focus.ti.com/lit/ds/symlink/tvp5150am1.pdf
3. Post-patch tvtime snapshot (same signal chain as #1, above):
http://www.booyaka.com/~paul/tvp5150/1b.png
Signed-off-by: Paul Walmsley <paul@booyaka.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
2962fc0120
