V4L2-TRACER(1)                   User Commands                  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>.json


DESCRIPTION
       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.
              <dev> must be a digit corresponding to an existing
              /dev/video<dev>

       -m, --media <dev>
              Use a different media device than specified in the trace file.
              <dev> must be a digit corresponding to an existing
              /dev/media<dev>


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.

v4l-utils 1.32.0                 November 2022                  V4L2-TRACER(1)