June 2022 - ffmpeg-devel - lists.ffmpeg.org

[PATCH] lavf/mpeg.c: improve readability of packet identification logic
by Scott Theisen 16 Sep '22

16 Sep '22

switch-case over es_type and then perform a linear search over startcode. --- libavformat/mpeg.c | 215 ++++++++++++++++++++++++++++----------------- 1 file changed, 132 insertions(+), 83 deletions(-) diff --git a/libavformat/mpeg.c b/libavformat/mpeg.c index ca15d9f241..c1b1c7e7de 100644 --- a/libavformat/mpeg.c +++ b/libavformat/mpeg.c @@ -19,6 +19,8 @@ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ +#include <stdbool.h> + #include "libavutil/channel_layout.h" #include "avformat.h" #include "avio_internal.h" @@ -480,6 +482,7 @@ static int mpegps_read_packet(AVFormatContext *s, AVStream *st; FFStream *sti; int len, startcode, i, es_type, ret; + bool identified = false; int pcm_dvd = 0; int request_probe= 0; enum AVCodecID codec_id = AV_CODEC_ID_NONE; @@ -520,92 +523,138 @@ redo: goto found; } + // identify packet encoding + identified = true; es_type = m->psm_es_type[startcode & 0xff]; - if (es_type == STREAM_TYPE_VIDEO_MPEG1) { - codec_id = AV_CODEC_ID_MPEG2VIDEO; - type = AVMEDIA_TYPE_VIDEO; - } else if (es_type == STREAM_TYPE_VIDEO_MPEG2) { - codec_id = AV_CODEC_ID_MPEG2VIDEO; - type = AVMEDIA_TYPE_VIDEO; - } else if (es_type == STREAM_TYPE_AUDIO_MPEG1 || - es_type == STREAM_TYPE_AUDIO_MPEG2) { - codec_id = AV_CODEC_ID_MP3; - type = AVMEDIA_TYPE_AUDIO; - } else if (es_type == STREAM_TYPE_AUDIO_AAC) { - codec_id = AV_CODEC_ID_AAC; - type = AVMEDIA_TYPE_AUDIO; - } else if (es_type == STREAM_TYPE_VIDEO_MPEG4) { - codec_id = AV_CODEC_ID_MPEG4; - type = AVMEDIA_TYPE_VIDEO; - } else if (es_type == STREAM_TYPE_VIDEO_H264) { - codec_id = AV_CODEC_ID_H264; - type = AVMEDIA_TYPE_VIDEO; - } else if (es_type == STREAM_TYPE_VIDEO_HEVC) { - codec_id = AV_CODEC_ID_HEVC; - type = AVMEDIA_TYPE_VIDEO; - } else if (es_type == STREAM_TYPE_AUDIO_AC3) { - codec_id = AV_CODEC_ID_AC3; - type = AVMEDIA_TYPE_AUDIO; - } else if (m->imkh_cctv && es_type == 0x91) { - codec_id = AV_CODEC_ID_PCM_MULAW; - type = AVMEDIA_TYPE_AUDIO; - } else if (startcode >= 0x1e0 && startcode <= 0x1ef) { - static const unsigned char avs_seqh[4] = { 0, 0, 1, 0xb0 }; - unsigned char buf[8]; - - avio_read(s->pb, buf, 8); - avio_seek(s->pb, -8, SEEK_CUR); - if (!memcmp(buf, avs_seqh, 4) && (buf[6] != 0 || buf[7] != 1)) - codec_id = AV_CODEC_ID_CAVS; - else - request_probe= 1; - type = AVMEDIA_TYPE_VIDEO; - } else if (startcode == PRIVATE_STREAM_2) { - type = AVMEDIA_TYPE_DATA; - codec_id = AV_CODEC_ID_DVD_NAV; - } else if (startcode >= 0x1c0 && startcode <= 0x1df) { - type = AVMEDIA_TYPE_AUDIO; - if (m->sofdec > 0) { - codec_id = AV_CODEC_ID_ADPCM_ADX; - // Auto-detect AC-3 - request_probe = 50; - } else if (m->imkh_cctv && startcode == 0x1c0 && len > 80) { - codec_id = AV_CODEC_ID_PCM_ALAW; - request_probe = 50; - } else { - codec_id = AV_CODEC_ID_MP2; - if (m->imkh_cctv) - request_probe = 25; + switch (es_type) { + case STREAM_TYPE_VIDEO_MPEG1: // 0x01 + case STREAM_TYPE_VIDEO_MPEG2: // 0x02 + codec_id = AV_CODEC_ID_MPEG2VIDEO; + type = AVMEDIA_TYPE_VIDEO; + break; + case STREAM_TYPE_VIDEO_MPEG4: // 0x10 + codec_id = AV_CODEC_ID_MPEG4; + type = AVMEDIA_TYPE_VIDEO; + break; + case STREAM_TYPE_VIDEO_H264: // 0x1B + codec_id = AV_CODEC_ID_H264; + type = AVMEDIA_TYPE_VIDEO; + break; + case STREAM_TYPE_VIDEO_HEVC: // 0x24 + codec_id = AV_CODEC_ID_HEVC; + type = AVMEDIA_TYPE_VIDEO; + break; + case STREAM_TYPE_AUDIO_MPEG1: // 0x03 + case STREAM_TYPE_AUDIO_MPEG2: // 0x04 + codec_id = AV_CODEC_ID_MP3; + type = AVMEDIA_TYPE_AUDIO; + break; + case STREAM_TYPE_AUDIO_AAC: // 0x0F + codec_id = AV_CODEC_ID_AAC; + type = AVMEDIA_TYPE_AUDIO; + break; + case STREAM_TYPE_AUDIO_AC3: // 0x81 + codec_id = AV_CODEC_ID_AC3; + type = AVMEDIA_TYPE_AUDIO; + break; + default: + if (m->imkh_cctv && es_type == 0x91) { + codec_id = AV_CODEC_ID_PCM_MULAW; + type = AVMEDIA_TYPE_AUDIO; + break; + } + identified = false; + break; + } + if (!identified) { + identified = true; + if (startcode < 0x20) { + identified = false; } - } else if (startcode >= 0x80 && startcode <= 0x87) { - type = AVMEDIA_TYPE_AUDIO; - codec_id = AV_CODEC_ID_AC3; - } else if ((startcode >= 0x88 && startcode <= 0x8f) || - (startcode >= 0x98 && startcode <= 0x9f)) { - /* 0x90 - 0x97 is reserved for SDDS in DVD specs */ - type = AVMEDIA_TYPE_AUDIO; - codec_id = AV_CODEC_ID_DTS; - } else if (startcode >= 0xa0 && startcode <= 0xaf) { - type = AVMEDIA_TYPE_AUDIO; - if (!pcm_dvd) { - codec_id = AV_CODEC_ID_MLP; - } else { - codec_id = AV_CODEC_ID_PCM_DVD; + else if (startcode <= 0x3F) { // 0x20 to 0x3F + type = AVMEDIA_TYPE_SUBTITLE; + codec_id = AV_CODEC_ID_DVD_SUBTITLE; } - } else if (startcode >= 0xb0 && startcode <= 0xbf) { - type = AVMEDIA_TYPE_AUDIO; - codec_id = AV_CODEC_ID_TRUEHD; - } else if (startcode >= 0xc0 && startcode <= 0xcf) { - /* Used for both AC-3 and E-AC-3 in EVOB files */ - type = AVMEDIA_TYPE_AUDIO; - codec_id = AV_CODEC_ID_AC3; - } else if (startcode >= 0x20 && startcode <= 0x3f) { - type = AVMEDIA_TYPE_SUBTITLE; - codec_id = AV_CODEC_ID_DVD_SUBTITLE; - } else if (startcode >= 0xfd55 && startcode <= 0xfd5f) { - type = AVMEDIA_TYPE_VIDEO; - codec_id = AV_CODEC_ID_VC1; - } else { + else if (startcode < 0x80) { // 0x40 to 0x7F + identified = false; + } + else if (startcode <= 0x87) { // 0x80 to 0x87 + type = AVMEDIA_TYPE_AUDIO; + codec_id = AV_CODEC_ID_AC3; + } + else if (startcode <= 0x8F) { // 0x88 to 0x8F (to 0x9F excluding 0x90 - 0x97) + type = AVMEDIA_TYPE_AUDIO; + codec_id = AV_CODEC_ID_DTS; + } + else if (startcode <= 0x97) { // exclude 0x90 to 0x97 + identified = false; // 0x90 - 0x97 is reserved for SDDS in DVD specs + } + else if (startcode <= 0x9F) { // 0x98 to 0x9F (from 0x88 excluding 0x90 - 0x97) + type = AVMEDIA_TYPE_AUDIO; + codec_id = AV_CODEC_ID_DTS; + } + else if (startcode <= 0xAF) { // 0xA0 to 0xAF + type = AVMEDIA_TYPE_AUDIO; + codec_id = (!pcm_dvd) ? AV_CODEC_ID_MLP : AV_CODEC_ID_PCM_DVD; + } + else if (startcode <= 0xBF) { // 0xB0 to 0xBF + type = AVMEDIA_TYPE_AUDIO; + codec_id = AV_CODEC_ID_TRUEHD; + } + else if (startcode <= 0xCF) { // 0xC0 to 0xCF + /* Used for both AC-3 and E-AC-3 in EVOB files */ + type = AVMEDIA_TYPE_AUDIO; + codec_id = AV_CODEC_ID_AC3; + } + else if (startcode < 0x1BF) { // 0xD0 to 0x1BE + identified = false; + } + else if (startcode == PRIVATE_STREAM_2) { // 0x1BF + type = AVMEDIA_TYPE_DATA; + codec_id = AV_CODEC_ID_DVD_NAV; + } + else if (startcode <= 0x1DF) { // 0x1C0 to 0x1DF + type = AVMEDIA_TYPE_AUDIO; + if (m->sofdec > 0) { + codec_id = AV_CODEC_ID_ADPCM_ADX; + // Auto-detect AC-3 + request_probe = 50; + } + else if (m->imkh_cctv && startcode == 0x1c0 && len > 80) { + codec_id = AV_CODEC_ID_PCM_ALAW; + request_probe = 50; + } + else { + codec_id = AV_CODEC_ID_MP2; + if (m->imkh_cctv) + request_probe = 25; + } + } + else if (startcode <= 0x1EF) { // 0x1E0 to 0x1EF + static const unsigned char avs_seqh[4] = { 0, 0, 1, 0xb0 }; + unsigned char buf[8]; + + avio_read(s->pb, buf, 8); + avio_seek(s->pb, -8, SEEK_CUR); + if (!memcmp(buf, avs_seqh, 4) && (buf[6] != 0 || buf[7] != 1)) + codec_id = AV_CODEC_ID_CAVS; + else + request_probe= 1; + type = AVMEDIA_TYPE_VIDEO; + } + else if (startcode < 0xFD55) { // 0x01F0 to 0xFD54 + identified = false; + } + else if (startcode <= 0xFD5F) { // 0xFD55 to 0xFD5F + type = AVMEDIA_TYPE_VIDEO; + codec_id = AV_CODEC_ID_VC1; + } + else { + identified = false; + } + } + + if (!identified) { skip: /* skip packet */ avio_skip(s->pb, len); -- 2.32.0

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[PATCH 0/8] rewrite avpriv_find_start_code() for clarity
by Scott Theisen 16 Sep '22

16 Sep '22

I am endeavoring to reduce MythTV’s downstream changes to FFmpeg. avpriv_find_start_code() is one of the internal FFmpeg functions that MythTV uses. I was planning on copying it into MythTV to eventually eliminate all uses of internal FFmpeg headers; however, what avpriv_find_start_code() actually does was not very clear. Therefore, I rewrote it and added comments to make its purpose and effects clearer.

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[PATCH] lavu: make av_get_media_type_string() never return NULL
by Scott Theisen 16 Sep '22

16 Sep '22

printf %s with a null pointer is undefined behavior --- libavutil/avutil.h | 3 +-- libavutil/utils.c | 3 ++- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/libavutil/avutil.h b/libavutil/avutil.h index 4d633156d1..4bd468d72f 100644 --- a/libavutil/avutil.h +++ b/libavutil/avutil.h @@ -207,8 +207,7 @@ enum AVMediaType { }; /** - * Return a string describing the media_type enum, NULL if media_type - * is unknown. + * Return a string describing the media_type enum, never NULL. */ const char *av_get_media_type_string(enum AVMediaType media_type); diff --git a/libavutil/utils.c b/libavutil/utils.c index ea9b5097b8..c85d7abace 100644 --- a/libavutil/utils.c +++ b/libavutil/utils.c @@ -71,12 +71,13 @@ const char *avutil_license(void) const char *av_get_media_type_string(enum AVMediaType media_type) { switch (media_type) { + case AVMEDIA_TYPE_UNKNOWN: return "unknown"; case AVMEDIA_TYPE_VIDEO: return "video"; case AVMEDIA_TYPE_AUDIO: return "audio"; case AVMEDIA_TYPE_DATA: return "data"; case AVMEDIA_TYPE_SUBTITLE: return "subtitle"; case AVMEDIA_TYPE_ATTACHMENT: return "attachment"; - default: return NULL; + default: return "invalid"; } } -- 2.32.0

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[PATCH] avcodec/arm/sbcenc: save callee preserved vfp registers
by James Cowgill 12 Sep '22

12 Sep '22

When compiling FFmpeg with GCC-9, some very random segfaults were observed in code which had previously called down into the SBC encoder NEON assembly routines. This was caused by these functions clobbering some of the vfp callee saved registers (d8 - d15 aka q4 - q7). GCC was using these registers to save local variables, but after these functions returned, they would contain garbage. Fix by saving the relevant registers on the stack in the affected functions. Signed-off-by: James Cowgill <jcowgill(a)debian.org> --- libavcodec/arm/sbcdsp_neon.S | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/libavcodec/arm/sbcdsp_neon.S b/libavcodec/arm/sbcdsp_neon.S index d83d21d202..aa03800096 100644 --- a/libavcodec/arm/sbcdsp_neon.S +++ b/libavcodec/arm/sbcdsp_neon.S @@ -38,6 +38,8 @@ function ff_sbc_analyze_4_neon, export=1 /* TODO: merge even and odd cases (or even merge all four calls to this * function) in order to have only aligned reads from 'in' array * and reduce number of load instructions */ + vpush {d8-d11} + vld1.16 {d4, d5}, [r0, :64]! vld1.16 {d8, d9}, [r2, :128]! @@ -84,6 +86,7 @@ function ff_sbc_analyze_4_neon, export=1 vst1.32 {d0, d1}, [r1, :128] + vpop {d8-d11} bx lr endfunc @@ -91,6 +94,8 @@ function ff_sbc_analyze_8_neon, export=1 /* TODO: merge even and odd cases (or even merge all four calls to this * function) in order to have only aligned reads from 'in' array * and reduce number of load instructions */ + vpush {d8-d15} + vld1.16 {d4, d5}, [r0, :64]! vld1.16 {d8, d9}, [r2, :128]! @@ -188,6 +193,7 @@ function ff_sbc_analyze_8_neon, export=1 vst1.32 {d0, d1, d2, d3}, [r1, :128] + vpop {d8-d15} bx lr endfunc -- 2.22.0

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[PATCH 1/3] avcodec/fmvc: Move frame allocation to a later stage
by Michael Niedermayer 08 Sep '22

08 Sep '22

This way more things are checked before allocation Signed-off-by: Michael Niedermayer <michael(a)niedermayer.cc> --- libavcodec/fmvc.c | 21 +++++++++++++++------ 1 file changed, 15 insertions(+), 6 deletions(-) diff --git a/libavcodec/fmvc.c b/libavcodec/fmvc.c index 4abf6d7048..912ad8fc82 100644 --- a/libavcodec/fmvc.c +++ b/libavcodec/fmvc.c @@ -401,20 +401,17 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *frame, GetByteContext *gb = &s->gb; PutByteContext *pb = &s->pb; int ret, y, x; + int key_frame; if (avpkt->size < 8) return AVERROR_INVALIDDATA; - if ((ret = ff_get_buffer(avctx, frame, 0)) < 0) - return ret; - bytestream2_init(gb, avpkt->data, avpkt->size); bytestream2_skip(gb, 2); - frame->key_frame = !!bytestream2_get_le16(gb); - frame->pict_type = frame->key_frame ? AV_PICTURE_TYPE_I : AV_PICTURE_TYPE_P; + key_frame = !!bytestream2_get_le16(gb); - if (frame->key_frame) { + if (key_frame) { const uint8_t *src; unsigned type, size; uint8_t *dst; @@ -434,6 +431,12 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *frame, return AVERROR_PATCHWELCOME; } + if ((ret = ff_get_buffer(avctx, frame, 0)) < 0) + return ret; + + frame->key_frame = 1; + frame->pict_type = AV_PICTURE_TYPE_I; + src = s->buffer; dst = frame->data[0] + (avctx->height - 1) * frame->linesize[0]; for (y = 0; y < avctx->height; y++) { @@ -514,6 +517,12 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *frame, dst = &rect[block_h * s->stride]; } + if ((ret = ff_get_buffer(avctx, frame, 0)) < 0) + return ret; + + frame->key_frame = 0; + frame->pict_type = AV_PICTURE_TYPE_P; + ssrc = s->buffer; ddst = frame->data[0] + (avctx->height - 1) * frame->linesize[0]; for (y = 0; y < avctx->height; y++) { -- 2.17.1

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[PATCH 0/3] avformat/avisynth: support frame properties
by Stephen Hutchinson 04 Sep '22

04 Sep '22

AviSynth+ 3.6.0 introduced support for frame properties, allowing various metadata to be passed between filters or read out by client programs. Using this, FFmpeg can read Color Range, Transfer Characteristics, Matrix, Color Primaries, Chroma Location, and Field Order information from AviSynth scripts. Reading frame properties through AviSynth's C interface was not possible until a few months ago, though, so client programs that use the C API need version 3.7.1 or higher to be able to take advantage of it. Incorporates a previous patch by emcodem that fixes setting field order on non-frameprop-aware versions of AviSynth. Stephen Hutchinson (2): avisynth: use AviSynth+'s frame properties to set various fields configure: check avisynth header version emcodem (1): avisynth: corrected interlace detection configure | 4 +- libavformat/avisynth.c | 266 ++++++++++++++++++++++++++++++++++++++--- 2 files changed, 253 insertions(+), 17 deletions(-) -- 2.32.0

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[PATCH] avfilter: add 3D scope multimedia filter
by Paul B Mahol 03 Sep '22

03 Sep '22

Hello, Patch attached.

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[PATCH 1/3] tools/target_dec_fuzzer: Adjust threshold for SIMBIOSIS_IMX
by Michael Niedermayer 02 Sep '22

02 Sep '22

Fixes: Timeout Fixes: 47892/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SIMBIOSIS_IMX_fuzzer-5160609278197760 Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg Signed-off-by: Michael Niedermayer <michael(a)niedermayer.cc> --- tools/target_dec_fuzzer.c | 1 + 1 file changed, 1 insertion(+) diff --git a/tools/target_dec_fuzzer.c b/tools/target_dec_fuzzer.c index fefc8514f0..8bf8761574 100644 --- a/tools/target_dec_fuzzer.c +++ b/tools/target_dec_fuzzer.c @@ -256,6 +256,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) { case AV_CODEC_ID_SANM: maxpixels /= 16; break; case AV_CODEC_ID_SCPR: maxpixels /= 32; break; case AV_CODEC_ID_SCREENPRESSO:maxpixels /= 64; break; + case AV_CODEC_ID_SIMBIOSIS_IMX: maxpixels /= 16384;break; case AV_CODEC_ID_SMACKVIDEO: maxpixels /= 64; break; case AV_CODEC_ID_SNOW: maxpixels /= 128; break; case AV_CODEC_ID_TARGA: maxpixels /= 128; break; -- 2.17.1

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[PATCH 1/3] checkasm/hevc_add_res: add 12bit test
by J. Dekker 18 Aug '22

18 Aug '22

Signed-off-by: J. Dekker <jdek(a)itanimul.li> --- tests/checkasm/hevc_add_res.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/tests/checkasm/hevc_add_res.c b/tests/checkasm/hevc_add_res.c index 0c896adaca..f17d121939 100644 --- a/tests/checkasm/hevc_add_res.c +++ b/tests/checkasm/hevc_add_res.c @@ -36,14 +36,14 @@ } \ } while (0) -#define randomize_buffers2(buf, size) \ +#define randomize_buffers2(buf, size, mask) \ do { \ int j; \ for (j = 0; j < size; j++) \ - AV_WN16A(buf + j * 2, rnd() & 0x3FF); \ + AV_WN16A(buf + j * 2, rnd() & mask); \ } while (0) -static void compare_add_res(int size, ptrdiff_t stride, int overflow_test) +static void compare_add_res(int size, ptrdiff_t stride, int overflow_test, int mask) { LOCAL_ALIGNED_32(int16_t, res0, [32 * 32]); LOCAL_ALIGNED_32(int16_t, res1, [32 * 32]); @@ -53,7 +53,7 @@ static void compare_add_res(int size, ptrdiff_t stride, int overflow_test) declare_func_emms(AV_CPU_FLAG_MMX, void, uint8_t *dst, int16_t *res, ptrdiff_t stride); randomize_buffers(res0, size); - randomize_buffers2(dst0, size); + randomize_buffers2(dst0, size, mask); if (overflow_test) res0[0] = 0x8000; memcpy(res1, res0, sizeof(*res0) * size); @@ -69,6 +69,7 @@ static void compare_add_res(int size, ptrdiff_t stride, int overflow_test) static void check_add_res(HEVCDSPContext h, int bit_depth) { int i; + int mask = bit_depth == 8 ? 0xFFFF : bit_depth == 10 ? 0x03FF : 0x07FF; for (i = 2; i <= 5; i++) { int block_size = 1 << i; @@ -76,9 +77,9 @@ static void check_add_res(HEVCDSPContext h, int bit_depth) ptrdiff_t stride = block_size << (bit_depth > 8); if (check_func(h.add_residual[i - 2], "hevc_add_res_%dx%d_%d", block_size, block_size, bit_depth)) { - compare_add_res(size, stride, 0); + compare_add_res(size, stride, 0, mask); // overflow test for res = -32768 - compare_add_res(size, stride, 1); + compare_add_res(size, stride, 1, mask); } } } @@ -87,7 +88,7 @@ void checkasm_check_hevc_add_res(void) { int bit_depth; - for (bit_depth = 8; bit_depth <= 10; bit_depth++) { + for (bit_depth = 8; bit_depth <= 12; bit_depth++) { HEVCDSPContext h; ff_hevc_dsp_init(&h, bit_depth); -- 2.32.0 (Apple Git-132)

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The case for a good string API
by Nicolas George 15 Aug '22

15 Aug '22

Hi. I will try again proposing a good string API for the project. But this time, instead of showing the implementation code, I will ask about the principle. So, please, read the argument, and give your opinion on the principle. If we agree on the principle, we can discuss the code then. * Why we need a better string API Strings are not the bulk of what we do, but for the user interface of things we have a LOT of functions that return strings: to describe a color space or a channel layout or a set of options. When the returned string is short, we use the good old “char *buf, size_t buf_size”. When it is long, we return a dynamically-allocated buffer. When the string is almost always short but can actually be very long, and the conversion is used in speed-critical code, we are screwed. With a good string API, we could use the same API everywhere, it would automatically use the most efficient memory scheme. Furthermore, if all our object→string functions have the same prototype, it makes it easier to use these functions as standardized callbacks and opens a whole lot of new possibilities of serialization features. Moreover, a good string API would bring quite a few extra benefits, with a few examples: easier to build strings from parts, less verbose and more robust error checking, the ability to use directly the string or buffering API of another library or language. So, even though strings are not the core of our thing, I think we should have a good string API, just like we have an API for efficient FFTs (which is the core of our thing). But let us discuss it further: * Objections and counter-objections - A string API adds complexity. Indeed, that is true. But the added complexity is clearly isolated in one or a few source files. In the rest of the code, it removes complexity (see less verbose error checking, easier to build strings from parts above). String conversion functions can happen once per short frame, for example in the ashowinfo filter. We have pools for frames and for buffers: we already consider that avoid once-per-frame memory allocations is worth the added complexity. A string API is just a step in the same direction. - An unusual API is annoying for people who will use it. Unless we messed up, if they use strings more than just a little, the benefits of the API is way worth the cost of learning. But some people use strings just a little. For them, who would be happy with a plain C string, we should make sure the required learning is very very limited. And we can: “instead of ‘buf, sizeof(buf)’, write ‘string_from_buffer(buf)”. That is all, in one short line I have documented how to use the API with the old patterns. There is a little more to write for people who want a dynamic buffer for an unlimited string (error checks are always annoying), but we can keep it under three minutes. * What string API we should use We have AVBprint, but the API is ugly, and it only brings a few of the benefits I promised. I have a proposal: AVWriter. I posted it last spring, here is an introduction on how to use it (with the implementation in the same thread): https://ffmpeg.org/pipermail/ffmpeg-devel/2021-April/279383.html * Conclusion Well, I am convinced, but what about you? 1. Do you think FFmpeg needs a good string API? If not, please explain why? 2. Assuming we agree ‘yes’ on the previous question, do you think AVWriter is a good candidate? If not, what else would you propose? Regards, -- Nicolas George

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