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+date = '2026-06-17T17:50:30-05:00'
+title = 'FFmpeg'
++++
+
+## Websites
+
+* [ffmpeg.org](https://ffmpeg.org/)
+* [code.ffmpeg.org](https://code.ffmpeg.org/FFmpeg/FFmpeg) - code forge
+* [trac.ffmpeg.org](https://trac.ffmpeg.org/query?status=!closed&type=defect&order=id&desc=1) - bug tracker, mostly abandoned in favor of forgejo
+* [ffmpeg-devel mailing list](https://lists.ffmpeg.org/mailman3/lists/ffmpeg-devel.ffmpeg.org/) - development mailing list, mostly abandoned in favor of forgejo
+* [ffmpeg-devel IRC](https://libera.catirclogs.org/ffmpeg-devel/2026-06) - development chat, very active
+* [patchwork.ffmpeg.org](https://patchwork.ffmpeg.org/project/ffmpeg/list/) - archive of patches sent to ffmpeg-devel
+
+## Documentation
+
+* Command-line tools, filters, etc: https://ffmpeg.org/ffmpeg-all.html
+* Component libraries: https://ffmpeg.org/doxygen/trunk/index.html
+
+## Building
+
+List all compile options:
+```
+$ ./configure --help | vim -
+```
+
+Quick development build; takes about 90 seconds on an M1 MacBook Air:
+```
+$ ./configure --disable-optimizations --disable-asm
+$ make -j $(nproc)
+$ make -j $(sysctl -n hw.logicalcpu)
+```
+
+Troubleshooting build:
+```
+$ ./configure --disable-optimizations --assert-level=2 --toolchain=clang-asan
+$ ./configure --disable-optimizations --assert-level=2 --toolchain=clang-asan-ubsan
+```
+
+`--enable-memory-poisoning` makes `av_malloc` and friends basically just do `memset(ptr, 0x2a, size)`. Does not add any asan-style bounds checking.
+
+## Regression testing
+
+FATE documentation: https://ffmpeg.org/fate.html, TLDR:
+```
+$ ./configure --disable-optimizations --assert-level=2 --toolchain=clang-asan --samples=$HOME/Proj/FFmpeg-FATE
+$ make
+$ make fate-rsync
+$ make fate
+```
+
+## Benchmarking
+
+checkasm docs: https://checkasm.videolan.me/
+
+Build within FFmpeg:
+```
+$ make checkasm
+```
+
+List tests:
+```
+$ ./tests/checkasm/checkasm --list-tests | sort | vim -
+
+```
+
+The easiest way to see what test calls what functions is to check the source code:
+<br>
+[`-> tests/checkasm/checkasm.c`](https://code.ffmpeg.org/FFmpeg/FFmpeg/src/branch/master/tests/checkasm/checkasm.c).
+
+Example:
+```
+$ ./tests/checkasm/checkasm --bench --test=vf_bwdif
+```
+<details>
+<summary>Output</summary>
+
+```
+checkasm:
+ - CPU: Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz (000906E9)
+ - Timing source: x86 (rdtsc)
+ - Bench duration: 1000 µs per function (4003730 cycles)
+ - Random seed: 2684063072
+C:
+ - vf_bwdif.bwdif8 [OK]
+ - vf_bwdif.bwdif10 [OK]
+ - vf_bwdif.bwdif8.line3 [OK]
+ - vf_bwdif.bwdif8.edge  [OK]
+ - vf_bwdif.bwdif8.intra [OK]
+SSE2:
+ - vf_bwdif.bwdif8       [OK]
+ - vf_bwdif.bwdif10      [OK]
+SSSE3:
+ - vf_bwdif.bwdif8       [OK]
+ - vf_bwdif.bwdif10      [OK]
+AVX2:
+ - vf_bwdif.bwdif8       [OK]
+ - vf_bwdif.bwdif10      [OK]
+checkasm: all 6 tests passed
+Benchmark results:
+  name                       cycles (vs ref)
+  bwdif8_c:                 28876.2
+  bwdif8_sse2:               1056.1 (25.12x)
+  bwdif8_ssse3:               870.5 (22.92x)
+  bwdif8_avx2:                550.6 (40.40x)
+  bwdif8.edge.s0.p0_c:       1373.2
+  bwdif8.edge.s0.p1_c:       1310.2
+  bwdif8.edge.s1.p0_c:       5368.5
+  bwdif8.edge.s1.p1_c:       5824.8
+  bwdif8.intra_c:             584.1
+  bwdif8.line3.rnd.p0_c:    40020.9
+  bwdif8.line3.rnd.p1_c:    30286.6
+  bwdif10_c:                27988.9
+  bwdif10_sse2:               935.6 (27.51x)
+  bwdif10_ssse3:              864.2 (27.04x)
+  bwdif10_avx2:               594.3 (36.53x)
+```
+
+</details>
+
+## libavformat architecture
+
+Note: This is all based off of FFmpeg 8.1.2 (commit `38b88335f99e76ed89ff3c93f877fdefce736c13`)
+
+Stepping through [`doc/examples/remux.c`](https://code.ffmpeg.org/FFmpeg/FFmpeg/src/commit/38b88335f99e76ed89ff3c93f877fdefce736c13/doc/examples/remux.c):
+
+<style>
+.ffstackframe {
+	border-left: 2px solid #5555FF;
+	border-top: 1px solid #AAAAAA;
+	border-bottom: 1px solid #AAAAAA;
+	padding-left: 20px;
+}
+.ffstackframe > * {
+	margin-top: 0;
+	margin-bottom: 0;
+}
+</style>
+
+<div class="ffstackframe">
+
+[`doc/examples/remux.c:75`](https://code.ffmpeg.org/FFmpeg/FFmpeg/src/commit/38b88335f99e76ed89ff3c93f877fdefce736c13/doc/examples/remux.c#L75):
+`main` calls `avformat_open_input`.
+
+
+<div class="ffstackframe">
+
+[`libavformat/demux.c:241`](https://code.ffmpeg.org/FFmpeg/FFmpeg/src/commit/38b88335f99e76ed89ff3c93f877fdefce736c13/libavformat/demux.c#L241):
+`avformat_open_input` calls `avformat_alloc_context` to allocate memory.
+
+[`libavformat/demux.c:266`](https://code.ffmpeg.org/FFmpeg/FFmpeg/src/commit/38b88335f99e76ed89ff3c93f877fdefce736c13/libavformat/demux.c#L266):
+`avformat_open_input` calls `init_input`.
+
+<div class="ffstackframe">
+
+[`libavformat/demux.c:185`](https://code.ffmpeg.org/FFmpeg/FFmpeg/src/commit/38b88335f99e76ed89ff3c93f877fdefce736c13/libavformat/demux.c#L185):
+`init_input` calls `av_probe_input_buffer2`, which reads the first 2048 bytes of the input file
+and passes it to `av_probe_input_format2`, which calls `avprobe_input_format3`.
+
+<div class="ffstackframe">
+
+[`libavformat/format.c:175`](https://code.ffmpeg.org/FFmpeg/FFmpeg/src/commit/38b88335f99e76ed89ff3c93f877fdefce736c13/libavformat/format.c#L175):
+`av_probe_input_format3` attemptes to locate id3 tags within the buffer
+
+[`libavformat/format.c:191`](https://code.ffmpeg.org/FFmpeg/FFmpeg/src/commit/38b88335f99e76ed89ff3c93f877fdefce736c13/libavformat/format.c#L191):
+`av_probe_input_format3` iterates over each registered `FFInputFormat`, and calls the `probe`
+function pointer, if present. `probe` takes the buffer and returns a score that represents how
+likely the data matches that format. Some other factors are taken into account, such as the
+extension of the file and what id3 tags were found.
+
+The most likely `AVInputFormat *` (composite class in `FFInputFormat`) is returned if found,
+otherwise `NULL`.
+
+</div>
+
+[`libavformat/demux.c:305`](https://code.ffmpeg.org/FFmpeg/FFmpeg/src/commit/38b88335f99e76ed89ff3c93f877fdefce736c13/libavformat/demux.c#L305):
+`init_input` allocates any private data required by the `FFInputFormat`.
+
+[`libavformat/demux.c:322`](https://code.ffmpeg.org/FFmpeg/FFmpeg/src/commit/38b88335f99e76ed89ff3c93f877fdefce736c13/libavformat/demux.c#L322):
+`init_input` calls the `read_header` function pointer, if present.
+
+<div class="ffstackframe">
+
+`read_header` will typically call `avformat_new_stream` to allocate streams.
+
+</div>
+
+[`libavformat/demux.c:355`](https://code.ffmpeg.org/FFmpeg/FFmpeg/src/commit/38b88335f99e76ed89ff3c93f877fdefce736c13/libavformat/demux.c#L355):
+`init_input` calls the `update_stream_avctx`, which updates contexts for each stream. I am not sure
+why this is needed since no codecs should be open at this point, only demuxing.
+
+<div class="ffstackframe">
+
+[`libavformat/demux.c:194`](https://code.ffmpeg.org/FFmpeg/FFmpeg/src/commit/38b88335f99e76ed89ff3c93f877fdefce736c13/libavformat/demux.c#L194):
+`update_stream_avctx` iterates over each detected stream and calls `avcodec_parameters_to_context`
+if `FFStream->need_context_update == 1`.
+
+</div>
+</div>
+
+To summarize, `avformat_open_input` probes the file to detect the container, initializes the
+demuxer instance, and reads the file header.
+
+</div>
+
+[`doc/examples/remux.c:80`](https://code.ffmpeg.org/FFmpeg/FFmpeg/src/commit/38b88335f99e76ed89ff3c93f877fdefce736c13/doc/examples/remux.c#L80):
+`main` calls `avformat_find_stream_info`.
+
+</div>