On Mon, Feb 15, 2021 at 7:51 AM Andreas Rheinhardt <
andreas.rheinha...@gmail.com> wrote:
> sharpbai:
> > Before macOS 11, the encoded h264 sample contains fixed SEI before
> > IDR frame, which the content is below
> >
> > 06 05 10 b9 ed b9 30 5d 21 4b 71 83 71 2c 10 a3
> > 14 bb 29 80
> >
> > The length of the encoded SEI nalu is 20 byte. According to
> > the ITU-T H.264 Recommendation section 7.3.2.3.1, the last byte
> > 0x80 means type. Then there is no length byte, which make the
> > SEI nonstandard.
> >
> Wrong:
> 06: forbidden_zero_bit + nal_ref_idc + nal_unit_type (6 for SEI)
> 05: payload type 5 (user data unregistered) SEI message
> 10: length of this SEI message is 16
> b9-29: the payload of this SEI message (the first 12 byte are an uuid,
> the last are user_data_payload_byte)
> 80: rbsp_trailing_bits: the first bit is rbsp_stop_one_bit (equal to
> one), the remaining bits are padding (with value zero)
>
> You can use trace_headers to inspect this.
>
> (Notice that one needs to know the length of the NAL unit in advance
> before one can start parsing it; how one gets it depends upon the
> framing. There are two common methods for this: Annex B and mp4. The
> former works by using start codes 0x00 00 01 to mark the beginning of a
> new NAL, the latter prefixes the length of the NAL units to the units.)
>
> > On macOS 11, the encoded h264 sample still contains fixed SEI before
> > IDR frame, which length is 5 bytes longer than before.
> >
> > 06 05 10 b9 ed b9 30 5d 21 4b 71 83 71 2c 10 a3
> > 14 bb 29 80 00 00 03 00 01
> > ^^ ^^ ^^ ^^ ^^
>
> That looks as if there were a 00 00 00 01 startcode after the SEI that
> some tool has tried to 0x03 escape. That is a bug. Can you share samples
> containing these NAL units?
>
This file is inserting the emulation prevention byte 0x03. I can take a
look later today.
> >
> > This time type the content of the SEI has type 0 payload but
> > invalid length payload data, which violates recommendation
> > appendix D.
> >
> > Whether it is a bug or not, these SEI nalus should be erased to keep
> > the output bytestream not violating the standard. But we may
> > not come across the situration we do need these encoded SEI
> > nalu, so we just reserve a switch and set not to output by default.
> >
> > Signed-off-by: sharpbai <sharp...@gmail.com>
> > ---
> > libavcodec/videotoolboxenc.c | 51 +++++++++++++++++++++---------------
> > 1 file changed, 30 insertions(+), 21 deletions(-)
> >
> > diff --git a/libavcodec/videotoolboxenc.c b/libavcodec/videotoolboxenc.c
> > index cc08cf6a50..c240090f10 100644
> > --- a/libavcodec/videotoolboxenc.c
> > +++ b/libavcodec/videotoolboxenc.c
> > @@ -221,6 +221,7 @@ typedef struct VTEncContext {
> >
> > int64_t allow_sw;
> > int64_t require_sw;
> > + int64_t ignore_internal_sei;
> >
> > bool flushing;
> > bool has_b_frames;
> > @@ -1690,7 +1691,8 @@ static int copy_replace_length_codes(
> > CMSampleBufferRef sample_buffer,
> > ExtraSEI *sei,
> > uint8_t *dst_data,
> > - size_t dst_size)
> > + size_t dst_size,
> > + int ignore_internal_sei)
> > {
> > size_t src_size = CMSampleBufferGetTotalSampleSize(sample_buffer);
> > size_t remaining_src_size = src_size;
> > @@ -1707,8 +1709,8 @@ static int copy_replace_length_codes(
> > }
> >
> > while (remaining_src_size > 0) {
> > - size_t curr_src_len;
> > - size_t curr_dst_len;
> > + size_t curr_src_len = 0;
> > + size_t curr_dst_len = 0;
> > size_t box_len = 0;
> > size_t i;
> >
> > @@ -1740,7 +1742,8 @@ static int copy_replace_length_codes(
> > box_len |= size_buf[i];
> > }
> >
> > - if (sei && !wrote_sei && is_post_sei_nal_type(nal_type)) {
> > + if (sei && !wrote_sei &&
> > + (ignore_internal_sei ||
> is_post_sei_nal_type(nal_type))) {
> > //No SEI NAL unit - insert.
> > int wrote_bytes;
> >
> > @@ -1775,27 +1778,30 @@ static int copy_replace_length_codes(
> > }
> >
> > curr_src_len = box_len + length_code_size;
> > - curr_dst_len = box_len + sizeof(start_code);
> >
> > - if (remaining_src_size < curr_src_len) {
> > - return AVERROR_BUFFER_TOO_SMALL;
> > - }
> > + if (!(ignore_internal_sei && nal_type == H264_NAL_SEI)) {
> > + curr_dst_len = box_len + sizeof(start_code);
> >
> > - if (remaining_dst_size < curr_dst_len) {
> > - return AVERROR_BUFFER_TOO_SMALL;
> > - }
> > + if (remaining_src_size < curr_src_len) {
> > + return AVERROR_BUFFER_TOO_SMALL;
> > + }
> > +
> > + if (remaining_dst_size < curr_dst_len) {
> > + return AVERROR_BUFFER_TOO_SMALL;
> > + }
> >
> > - dst_box = dst_data + sizeof(start_code);
> > + dst_box = dst_data + sizeof(start_code);
> >
> > - memcpy(dst_data, start_code, sizeof(start_code));
> > - status = CMBlockBufferCopyDataBytes(block,
> > - src_offset +
> length_code_size,
> > - box_len,
> > - dst_box);
> > + memcpy(dst_data, start_code, sizeof(start_code));
> > + status = CMBlockBufferCopyDataBytes(block,
> > + src_offset +
> length_code_size,
> > + box_len,
> > + dst_box);
> >
> > - if (status) {
> > - av_log(avctx, AV_LOG_ERROR, "Cannot copy data: %d\n",
> status);
> > - return AVERROR_EXTERNAL;
> > + if (status) {
> > + av_log(avctx, AV_LOG_ERROR, "Cannot copy data: %d\n",
> status);
> > + return AVERROR_EXTERNAL;
> > + }
> > }
> >
> > if (sei && !wrote_sei && nal_type == H264_NAL_SEI) {
> > @@ -1931,7 +1937,8 @@ static int vtenc_cm_to_avpacket(
> > sample_buffer,
> > sei,
> > pkt->data + header_size,
> > - pkt->size - header_size
> > + pkt->size - header_size,
> > + vtctx->ignore_internal_sei
> > );
> >
> > if (status) {
> > @@ -2543,6 +2550,8 @@ static const enum AVPixelFormat hevc_pix_fmts[] = {
> > { .i64 = 0 }, 0, 1, VE }, \
> > { "require_sw", "Require software encoding", OFFSET(require_sw),
> AV_OPT_TYPE_BOOL, \
> > { .i64 = 0 }, 0, 1, VE }, \
> > + { "ignore_internal_sei", "Ignore SEI nalu generated by
> videotoolbox", OFFSET(ignore_internal_sei), AV_OPT_TYPE_BOOL, \
> > + { .i64 = 1 }, 0, 1, VE }, \
> > { "realtime", "Hint that encoding should happen in real-time if not
> faster (e.g. capturing from camera).", \
> > OFFSET(realtime), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, VE }, \
> > { "frames_before", "Other frames will come before the frames in
> this session. This helps smooth concatenation issues.", \
> >
>
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