| V4L2-TRACER(1) | 1.26.1"" | V4L2-TRACER(1) |
NAME
v4l2-tracer - An application to trace and replay stateless video decoding.
SYNOPSIS
v4l2-tracer [options] trace <tracee>
v4l2-tracer [options] retrace <trace_file>.json v4l2-tracer clean <file>.jsonDESCRIPTION
The v4l2-tracer utility traces, records and replays userspace applications that implement the v4l2 memory-to-memory stateless video decoder interface.
Trace
Trace system calls and video frame data passed by userspace application <tracee> to kernel driver. All stateless codec controls in user-space API can be traced. Outputs a JSON-formatted trace file.
Retrace
Read the JSON-formatted <trace_file>.json. Replay the same system calls and pass the same video frame data to kernel driver. Outputs a JSON-formatted retrace file.
Clean
Remove lines with irrelevant differences (e.g. file descriptors and memory addresses) from JSON files. Outputs a clean copy, not necessarily still in JSON-format.
OPTIONS
Common Options
- -c, --compact
- Write minimal whitespace in JSON file.
- -g, --debug
- Turn on verbose reporting plus additional debug info.
- -h, --help
- Display this message.
- -r, --raw
- Write decoded video frame data to JSON file.
- -v, --verbose
- Turn on verbose reporting.
- -y, --yuv
- Write decoded video frame data to yuv file.
Retrace Options
- -d, --device <dev>
- Use a different video device than specified in the trace file.
- -m, --media <dev>
- Use a different media device than specified in the trace file.
EXIT STATUS
On success, it returns 0. Otherwise, it will return 1 or an error code.
EXAMPLE
- Trace an application decoding VP8 video:
-
v4l2-tracer trace gst-launch-1.0 -- filesrc location=test-25fps.vp8 ! parsebin ! v4l2slvp8dec ! videocodectestsink
- A trace file is generated:
- 71827_trace.json
- Retrace the trace file:
-
v4l2-tracer retrace 71827_trace.json
- Specify device nodes if retracing on a different driver:
-
v4l2-tracer -d0 -m0 retrace 71827_trace.json
- A retrace file is generated:
- 71827_trace_retrace.json
- Remove file descriptors and addresses (optional):
-
v4l2-tracer clean 71827_trace.json
v4l2-tracer clean 71827_trace_retrace.json
- Clean files are generated for comparison:
-
clean_71827_trace.json
clean_71827_trace_retrace.json
BUGS
Bug reports or questions about this utility should be sent to the linux-media@vger.kernel.org mailinglist.
| November 2022 | v4l-utils |